diff --git a/src/main/java/de/ids_mannheim/korap/IndexInfo.java b/src/main/java/de/ids_mannheim/korap/IndexInfo.java
new file mode 100644
index 0000000..3b64b55
--- /dev/null
+++ b/src/main/java/de/ids_mannheim/korap/IndexInfo.java
@@ -0,0 +1,9 @@
+package de.ids_mannheim.korap;
+
+import java.util.Set;
+
+public interface IndexInfo {
+
+    abstract Set<String> getAllLeafFingerprints();
+    
+}
diff --git a/src/main/java/de/ids_mannheim/korap/Krill.java b/src/main/java/de/ids_mannheim/korap/Krill.java
index 6bee230..a99624b 100644
--- a/src/main/java/de/ids_mannheim/korap/Krill.java
+++ b/src/main/java/de/ids_mannheim/korap/Krill.java
@@ -9,6 +9,7 @@
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
 
+import de.ids_mannheim.korap.cache.VirtualCorpusCache;
 import de.ids_mannheim.korap.query.wrap.SpanQueryWrapper;
 import de.ids_mannheim.korap.response.Response;
 import de.ids_mannheim.korap.response.Result;
@@ -256,6 +257,7 @@
      */
     public Krill setIndex (KrillIndex index) {
         this.index = index;
+        VirtualCorpusCache.setIndexInfo(index);
         return this;
     };
 
@@ -272,6 +274,7 @@
      * @return The result as a {@link Result} object.
      */
     public Result apply (KrillIndex index) {
+        VirtualCorpusCache.setIndexInfo(index);
         return this.setIndex(index).apply();
     };
 
diff --git a/src/main/java/de/ids_mannheim/korap/KrillCollection.java b/src/main/java/de/ids_mannheim/korap/KrillCollection.java
index 628173b..4ec7752 100644
--- a/src/main/java/de/ids_mannheim/korap/KrillCollection.java
+++ b/src/main/java/de/ids_mannheim/korap/KrillCollection.java
@@ -8,6 +8,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;
+import java.util.Set;
 import java.util.zip.GZIPInputStream;
 
 import org.apache.commons.io.IOUtils;
@@ -32,16 +33,13 @@
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
 
-import de.ids_mannheim.korap.collection.CachedVCData;
 import de.ids_mannheim.korap.collection.CollectionBuilder;
 import de.ids_mannheim.korap.collection.DocBits;
 import de.ids_mannheim.korap.response.Notifications;
+import de.ids_mannheim.korap.util.Fingerprinter;
 import de.ids_mannheim.korap.util.KrillProperties;
 import de.ids_mannheim.korap.util.QueryException;
 import de.ids_mannheim.korap.util.StatusCodes;
-import net.sf.ehcache.Cache;
-import net.sf.ehcache.CacheManager;
-import net.sf.ehcache.Element;
 
 /**
  * Create a Virtual Collection of documents by means of a KoralQuery
@@ -61,10 +59,10 @@
  * See http://mail-archives.apache.org/mod_mbox/lucene-java-user/
  *     200805.mbox/%3C17080852.post@talk.nabble.com%3E
  */
-public final class KrillCollection extends Notifications {
+public final class KrillCollection extends Notifications implements IndexInfo {
     private KrillIndex index;
     private JsonNode json;
-    private CollectionBuilder cb = new CollectionBuilder();
+    private final CollectionBuilder cb = new CollectionBuilder(this);
     private CollectionBuilder.Interface cbi;
     private byte[] pl = new byte[4];
 
@@ -74,22 +72,17 @@
     // private static ByteBuffer bb = ByteBuffer.allocate(4);
 
     // Logger
-    private final static Logger log =
+     private final static Logger log =
             LoggerFactory.getLogger(KrillCollection.class);
-
     // This advices the java compiler to ignore all loggings
     public static final boolean DEBUG = false;
-
-    public static CacheManager cacheManager;
-    public static Cache cache;
+    private double start, end; // for debugging
 
     /**
      * Construct a new KrillCollection.
      * 
      */
-    public KrillCollection () {
-        initializeCache();
-    };
+    public KrillCollection () {};
 
 
     /**
@@ -99,7 +92,6 @@
      *            The {@link KrillIndex} object.
      */
     public KrillCollection (KrillIndex index) {
-        initializeCache();
         this.index = index;
     };
 
@@ -110,7 +102,6 @@
      *            The KoralQuery document as a JSON string.
      */
     public KrillCollection (String jsonString) {
-        initializeCache();
         try {
             JsonNode json = mapper.readTree(jsonString);
 
@@ -145,16 +136,7 @@
         };
     };
 
-    public static void initializeCache () {
-        if (cacheManager == null) {
-            cacheManager = CacheManager.newInstance();
-        }
-        if (cache == null) {
-            cache = cacheManager.getCache("named_vc");
-        }
-    }
-    
-    
+
     /**
      * Set the {@link KrillIndex} the virtual collection refers to.
      * 
@@ -175,7 +157,7 @@
      * @throws QueryException
      */
     public KrillCollection fromKoral (String jsonString) throws QueryException {
-		this.prefiltered = null;
+        this.prefiltered = null;
         try {
             this.fromKoral((JsonNode) mapper.readTree(jsonString));
         }
@@ -581,9 +563,35 @@
      */
     public FixedBitSet bits (LeafReaderContext atomic) throws IOException, QueryException {
 
+        // EM: really need a fixedBitset? 
+        // maybe better use org.apache.lucene.util.BitDocIdSet.Builder
+        // for automatic sparse bitset support
+        // appears possible by implementing a SparseDocBits class extending
+        // SparseFixedBitSet and implementing Serializable (only as marker interface)
         LeafReader r = atomic.reader();
         FixedBitSet bitset = new FixedBitSet(r.maxDoc());
-        DocIdSet docids = this.getDocIdSet(atomic, (Bits) r.getLiveDocs());
+
+        if (DEBUG) {
+            start = System.currentTimeMillis();
+        }
+        DocIdSet docids = null;
+        try {
+            docids = this.getDocIdSet(atomic, (Bits) r.getLiveDocs());
+        }
+        catch (RuntimeException e) {
+            Throwable t = e.getCause();
+            if (t instanceof IOException) {
+                throw new IOException(t);
+            }
+            else if (t instanceof QueryException) {
+                throw new QueryException(((QueryException) t).getErrorCode(), t.getLocalizedMessage());
+            }
+        }
+
+        if (DEBUG) {
+            end = System.currentTimeMillis();
+            log.info("getDocIdSet in bits: " + (end - start));
+        }
 
 
         if (docids == null) {
@@ -619,11 +627,13 @@
         int maxDoc = atomic.reader().maxDoc();
         FixedBitSet bitset = new FixedBitSet(maxDoc);
 
-        Filter filter;
-		if (this.cbi == null || (filter = this.toFilter()) == null) {
-			if (acceptDocs == null) return null;
-			bitset.set(0, maxDoc);
-		}
+        final Filter filter = this.toFilter();
+
+        if (filter == null) {
+            if (acceptDocs == null)
+                return null;
+            bitset.set(0, maxDoc);
+        }
 		else {
 
 			// Init vector
@@ -838,30 +848,13 @@
         };
         return str;
     };
-
-
-    public void storeInCache (String cacheKey) throws IOException, QueryException {
-        if (cacheKey ==null || cacheKey.isEmpty()) {
-            this.addError(StatusCodes.MISSING_ID,
-                    "Collection name is required for caching.");
-        }
+    public void storeInCache (String vcId) throws IOException, QueryException {
         
-        List<LeafReaderContext> leaves = this.index.reader().leaves();
-        Map<Integer, DocBits> docIdMap =
-                new HashMap<Integer, DocBits>(leaves.size());
+    }
 
-        for (LeafReaderContext context : leaves) {
-            if (docIdMap.get(context.hashCode()) == null) {
-                FixedBitSet bitset = bits(context);
-                DocBits docBits = new DocBits(bitset.getBits(), bitset.length());
-                docIdMap.put(context.hashCode(),
-                        docBits);
-            }
-        }
-
-        CachedVCData cc = new CachedVCData(docIdMap);
-        cache.put(new Element(cacheKey, cc));
-        this.cbi = cb.namedVC(cacheKey, cc);
+    @Override
+    public Set<String> getAllLeafFingerprints () {
+        return index.getAllLeafFingerprints();
     }
     
     /*
diff --git a/src/main/java/de/ids_mannheim/korap/KrillIndex.java b/src/main/java/de/ids_mannheim/korap/KrillIndex.java
index 60805bd..4e9ea06 100644
--- a/src/main/java/de/ids_mannheim/korap/KrillIndex.java
+++ b/src/main/java/de/ids_mannheim/korap/KrillIndex.java
@@ -3,16 +3,22 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.ByteBuffer;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.time.LocalDate;
 // Java core classes
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Base64;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Properties;
+import java.util.Set;
 import java.util.regex.Pattern;
 import java.util.zip.GZIPInputStream;
 
-import java.time.LocalDate;
-
-import java.security.NoSuchAlgorithmException;
-import java.security.MessageDigest;
-
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.analysis.miscellaneous.PerFieldAnalyzerWrapper;
 import org.apache.lucene.document.Document;
@@ -51,6 +57,7 @@
 
 import com.fasterxml.jackson.databind.ObjectMapper;
 
+import de.ids_mannheim.korap.cache.VirtualCorpusCache;
 // Krill classes
 import de.ids_mannheim.korap.index.FieldDocument;
 import de.ids_mannheim.korap.index.KeywordAnalyzer;
@@ -65,8 +72,9 @@
 import de.ids_mannheim.korap.response.Result;
 import de.ids_mannheim.korap.response.SearchContext;
 import de.ids_mannheim.korap.response.Text;
-import de.ids_mannheim.korap.util.KrillProperties;
+import de.ids_mannheim.korap.util.Fingerprinter;
 import de.ids_mannheim.korap.util.KrillDate;
+import de.ids_mannheim.korap.util.KrillProperties;
 import de.ids_mannheim.korap.util.QueryException;
 
 /**
@@ -135,7 +143,7 @@
   -> search for frequencies of VVFIN/gehen
   -> c:VVFIN:[^:]*?:gehen:past:...
 */
-public final class KrillIndex {
+public final class KrillIndex implements IndexInfo {
 
     // Logger
     private final static Logger log = LoggerFactory.getLogger(KrillIndex.class);
@@ -387,8 +395,6 @@
         this.writer().commit();
         commitCounter = 0;
         this.closeReader();
-        if (KrillCollection.cache != null)
-            KrillCollection.cache.removeAll();
     };
 
 
@@ -1715,25 +1721,9 @@
         if (this.reader() == null) {
             return "null";
         }
-
-        MessageDigest md;
-        try {
-            // MD5 used for fingerprinting (no security implications here)
-            md = MessageDigest.getInstance("MD5");
-        }
-        catch (NoSuchAlgorithmException e) {
-            log.error(e.getMessage());
-            return e.getMessage();
-        };
         
         String hash = this.reader().getCombinedCoreAndDeletesKey().toString();
-
-        md.update(hash.getBytes());
-
-        // Turn bytes into Base64 string
-        this.indexRevision = new String(
-            Base64.getEncoder().encode(md.digest())
-            );
+        this.indexRevision = Fingerprinter.create(hash);
 
         return this.indexRevision;
     };
@@ -1856,4 +1846,18 @@
     public boolean isReaderOpen () {
         return readerOpen;
     }
+
+
+    @Override
+    public Set<String> getAllLeafFingerprints () {
+        List<LeafReaderContext> leaves = this.reader().leaves();
+        Set<String> fingerprints = new HashSet<>(leaves.size() * 2);
+        for (LeafReaderContext context : leaves) {
+            String fp = Fingerprinter.create(
+                    context.reader().getCombinedCoreAndDeletesKey().toString());
+            fingerprints.add(fp);
+        }
+        return fingerprints;
+    }
+    
 };
diff --git a/src/main/java/de/ids_mannheim/korap/cache/VirtualCorpusCache.java b/src/main/java/de/ids_mannheim/korap/cache/VirtualCorpusCache.java
new file mode 100644
index 0000000..84cc29d
--- /dev/null
+++ b/src/main/java/de/ids_mannheim/korap/cache/VirtualCorpusCache.java
@@ -0,0 +1,248 @@
+package de.ids_mannheim.korap.cache;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Supplier;
+
+import org.apache.lucene.index.LeafReaderContext;
+
+import de.ids_mannheim.korap.IndexInfo;
+import de.ids_mannheim.korap.KrillIndex;
+import de.ids_mannheim.korap.collection.DocBits;
+import de.ids_mannheim.korap.collection.VirtualCorpusReferenceFilter;
+import de.ids_mannheim.korap.collection.VirtualCorpusReferenceFilter.DocBitsSupplier;
+import de.ids_mannheim.korap.util.Fingerprinter;
+import de.ids_mannheim.korap.util.QueryException;
+
+/**
+ * 
+ * @author margaretha
+ *
+ */
+public class VirtualCorpusCache {
+
+    public static final String CACHE_LOCATION = "vc-cache";
+    public static final int CAPACITY = 5;
+    public static final Map<String, Map<String, DocBits>> map = Collections
+            .synchronizedMap(new LinkedHashMap<String, Map<String, DocBits>>(
+                    CAPACITY, (float) 0.75, true) {
+
+                private static final long serialVersionUID = 1815514581428132435L;
+
+                @SuppressWarnings("rawtypes")
+                @Override
+                protected boolean removeEldestEntry (Map.Entry eldest) {
+                    return size() > CAPACITY;
+                }
+            });
+
+    private static IndexInfo indexInfo;
+
+    private static final Set<String> vcToCleanUp = Collections
+            .synchronizedSet(new HashSet<>());
+
+
+    public VirtualCorpusCache () {
+        File dir = new File(CACHE_LOCATION);
+        dir.mkdirs();
+    }
+
+
+    public static void storeOnDisk (String vcId, String leafFingerprint,
+            DocBits docBits) {
+        File dir = new File(CACHE_LOCATION + "/" + vcId);
+        if (!dir.exists()) {
+            dir.mkdirs();
+        }
+        
+        String filepath = dir + "/" + leafFingerprint;
+        File f = new File(filepath);
+        if (f.exists()) {
+            f.delete();
+        }
+        try {
+            ObjectOutputStream os = new ObjectOutputStream(
+                    new FileOutputStream(f));
+            os.writeObject(docBits);
+            os.close();
+        }
+        catch (IOException e) {
+            e.printStackTrace();
+            System.err.println("Cannot write " + filepath);
+        }
+    }
+
+
+    public static void store (String vcId, Map<String, DocBits> vcData) {
+        map.put(vcId, vcData);
+        for (String leafFingerprint : vcData.keySet()) {
+            storeOnDisk(vcId, leafFingerprint, vcData.get(leafFingerprint));
+        }
+
+    }
+
+    public static void store (String vcId, KrillIndex index)
+            throws QueryException, IOException {
+        
+        DocBitsSupplier docBitsSupplier = new VirtualCorpusReferenceFilter(
+                vcId).new DocBitsSupplier();
+        String leafFingerprint;
+        for (LeafReaderContext context : index.reader().leaves()) {
+            leafFingerprint = Fingerprinter.create(
+                    context.reader().getCombinedCoreAndDeletesKey().toString());
+
+            getDocBits(vcId, leafFingerprint, () -> {
+                try {
+                    return docBitsSupplier.supplyDocBits(context,
+                            context.reader().getLiveDocs());
+                }
+                catch (IOException | QueryException e) {
+                    throw new RuntimeException(e);
+                }
+            });
+        }
+    }
+
+
+    public static Map<String, DocBits> retrieve (String vcId) {
+        if (map.containsKey(vcId)) {
+            return map.get(vcId);
+        }
+        Map<String, DocBits> vcData = null;
+        File dir = new File(CACHE_LOCATION + "/" + vcId);
+        if (dir.exists()) {
+            vcData = new HashMap<String, DocBits>();
+            for (File f : dir.listFiles()) {
+                ObjectInputStream ois;
+                try {
+                    ois = new ObjectInputStream(new FileInputStream(f));
+                    DocBits d = (DocBits) ois.readObject();
+                    vcData.put(f.getName(), d);
+                    ois.close();
+                }
+                catch (IOException | ClassNotFoundException e) {
+                    return null;
+                }
+            }
+            map.put(vcId, vcData);
+        }
+        return vcData;
+
+    }
+
+
+    public static boolean contains (String vcId) {
+        if (map.containsKey(vcId)) {
+            return true;
+        }
+        else {
+            File f = new File(CACHE_LOCATION + "/" + vcId);
+            return f.exists();
+        }
+    }
+
+
+    public static void reset () {
+        vcToCleanUp.clear();
+        map.clear();
+
+        File vcCache = new File(VirtualCorpusCache.CACHE_LOCATION + "/");
+        for (File vc : vcCache.listFiles()) {
+            for (File f : vc.listFiles()) {
+                if (f.exists()) {
+                    f.delete();
+                }
+            }
+            vc.delete();
+        }
+        vcCache.delete();
+    }
+    
+    /**
+     * When the VC cache knows that a leaf-fingerprint is not in the
+     * map of a VC, it is marked for clean up. The cached VC will be
+     * cleaned up, next time a VC Reference is created.
+     * see {@link #getDocBits(String, String, Supplier)}
+     */
+    public static void setIndexInfo (IndexInfo indexInfo) {
+        VirtualCorpusCache.indexInfo = indexInfo;
+        synchronized (vcToCleanUp) {
+            if (!vcToCleanUp.isEmpty()) {
+                cleanup();
+            }
+        }
+    }
+
+
+    private static void cleanup () {
+        final Set<String> currentLeafFingerprints = indexInfo
+                .getAllLeafFingerprints();
+        Map<String, DocBits> vcData;
+        for (String vcId : vcToCleanUp) {
+            vcData = map.get(vcId);
+            vcData.keySet()
+                    .removeIf(storedFingerPrint -> currentLeafFingerprints
+                            .contains(storedFingerPrint) == false);
+            store(vcId, vcData);
+        }
+        vcToCleanUp.clear();
+    }
+
+
+    /**
+     * Gets DocBits for a single leaf from the VC cache or calculates
+     * and stores it, if it doesn't exist in the cache. This can
+     * happen when:
+     * <ul>
+     * <li> The VC has not been cached before</li>
+     * <p>The VC will be cached with a single leaf-fingerprint in a
+     * leafToDocBitMap. The map will be updated for the other leaf-
+     * fingerprints and thus be cleaned up once.
+     * </p>
+     * <li>The index has been updated</li>
+     * <p>
+     * In this case, the VC may contain old leaf-fingerprints. It will
+     * be clean up when the index is used next time.
+     * </p>
+     * </ul>
+     * 
+     * @see #setIndexInfo(IndexInfo)
+     * @param vcId
+     * @param leafFingerprint
+     * @param calculateDocBits
+     *            a supplier calculating the DocBits
+     * @return DocBits
+     */
+    public static DocBits getDocBits (String vcId, String leafFingerprint,
+            Supplier<DocBits> calculateDocBits) {
+        DocBits docBits = null;
+        Map<String, DocBits> leafToDocBitMap = retrieve(vcId);
+        if (leafToDocBitMap == null) {
+            leafToDocBitMap = Collections
+                    .synchronizedMap(new HashMap<String, DocBits>());
+            map.put(vcId, leafToDocBitMap);
+        }
+        else {
+            docBits = leafToDocBitMap.get(leafFingerprint);
+            if (docBits == null) {
+                vcToCleanUp.add(vcId);
+            }
+        }
+        if (docBits == null) {
+            docBits = calculateDocBits.get();
+            leafToDocBitMap.put(leafFingerprint, docBits);
+            storeOnDisk(vcId, leafFingerprint, docBits);
+        }
+        return docBits;
+    }
+}
diff --git a/src/main/java/de/ids_mannheim/korap/collection/CachedVCData.java b/src/main/java/de/ids_mannheim/korap/collection/CachedVCData.java
deleted file mode 100644
index ca97d52..0000000
--- a/src/main/java/de/ids_mannheim/korap/collection/CachedVCData.java
+++ /dev/null
@@ -1,77 +0,0 @@
-package de.ids_mannheim.korap.collection;
-
-import java.io.ByteArrayInputStream;
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
-import java.io.ObjectInputStream;
-import java.io.ObjectOutputStream;
-import java.io.Serializable;
-import java.util.Map;
-
-/**
- * Virtual corpus data to cache
- * 
- * @author margaretha
- *
- */
-public class CachedVCData implements Serializable {
-
-    /**
-     * Auto generated
-     * 
-     */
-    private static final long serialVersionUID = 5635087441839303653L;
-
-    private Map<Integer, DocBits> docIdMap;
-
-    public CachedVCData (Map<Integer, DocBits> docIdMap) {
-        this.docIdMap = docIdMap;
-    }
-
-    public Map<Integer, DocBits> getDocIdMap () {
-        return docIdMap;
-    }
-
-    public void setDocIdMap (Map<Integer, DocBits> docIdMap) {
-        this.docIdMap = docIdMap;
-    }
-
-    // EM: for optimization. has not been checked.
-    // ehcache retrieves a byte[] much faster than a map, however,
-    // there is an additional cost for converting a map to a byte[]
-    // and vice versa.
-
-    private byte[] toByteArray () throws IOException {
-        ByteArrayOutputStream bos = new ByteArrayOutputStream();
-        ObjectOutputStream oos = new ObjectOutputStream(bos);
-        oos.writeObject(docIdMap);
-        oos.flush();
-        return bos.toByteArray();
-    }
-
-    private Map<Integer, DocBits> toMap (byte[] bytes)
-            throws ClassNotFoundException, IOException {
-        ByteArrayInputStream bis = null;
-        ObjectInputStream ois = null;
-        Map<Integer, DocBits> map = null;
-        try {
-            bis = new ByteArrayInputStream(bytes);
-            ois = new ObjectInputStream(bis);
-            map = (Map<Integer, DocBits>) ois.readObject();
-
-        }
-        finally {
-            if (bis != null) {
-                bis.close();
-            }
-            if (ois != null) {
-                ois.close();
-            }
-        }
-        return map;
-    }
-
-	public String toString () {
-		return this.docIdMap.toString();
-	}
-}
diff --git a/src/main/java/de/ids_mannheim/korap/collection/CachedVCFilter.java b/src/main/java/de/ids_mannheim/korap/collection/CachedVCFilter.java
deleted file mode 100644
index de851c1..0000000
--- a/src/main/java/de/ids_mannheim/korap/collection/CachedVCFilter.java
+++ /dev/null
@@ -1,50 +0,0 @@
-package de.ids_mannheim.korap.collection;
-
-import java.io.IOException;
-
-import org.apache.logging.log4j.LogManager;
-import org.apache.logging.log4j.Logger;
-import org.apache.lucene.index.LeafReaderContext;
-import org.apache.lucene.search.DocIdSet;
-import org.apache.lucene.search.Filter;
-import org.apache.lucene.util.Bits;
-
-/**
- * Filter for virtual corpus/collection existing in the cache.
- * 
- * @author margaretha
- *
- */
-public class CachedVCFilter extends Filter {
-
-    public static final boolean DEBUG = false;
-
-    public static Logger jlog = LogManager.getLogger(CachedVCFilter.class);
-
-    private CachedVCData cachedCollection;
-    private String cacheKey;
-
-    public CachedVCFilter (String cacheKey, CachedVCData cachedCollection) {
-        this.cacheKey = cacheKey;
-        this.cachedCollection = cachedCollection;
-    }
-
-    @Override
-    public DocIdSet getDocIdSet (LeafReaderContext context, Bits acceptDocs)
-            throws IOException {
-        DocBits docBits =
-                cachedCollection.getDocIdMap().get(context.hashCode());
-
-        if (docBits == null) {
-            if (DEBUG)
-                jlog.debug("LeafReaderContext is not found in the cache.");
-            return null;
-        }
-        return docBits.createBitDocIdSet();
-    }
-
-    @Override
-    public String toString () {
-        return "referTo(cached:" + this.cacheKey + ")";
-    };
-}
diff --git a/src/main/java/de/ids_mannheim/korap/collection/CollectionBuilder.java b/src/main/java/de/ids_mannheim/korap/collection/CollectionBuilder.java
index 9f6dbe7..9f7e30f 100644
--- a/src/main/java/de/ids_mannheim/korap/collection/CollectionBuilder.java
+++ b/src/main/java/de/ids_mannheim/korap/collection/CollectionBuilder.java
@@ -1,15 +1,9 @@
 package de.ids_mannheim.korap.collection;
 
-import java.io.File;
-import java.io.FileInputStream;
 import java.io.IOException;
 import java.util.ArrayList;
-import java.util.HashMap;
 import java.util.Iterator;
-import java.util.Map;
-import java.util.Properties;
 
-import org.apache.commons.io.IOUtils;
 import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
 import org.apache.lucene.queries.TermsFilter;
 import org.apache.lucene.search.Filter;
@@ -20,14 +14,11 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import de.ids_mannheim.korap.IndexInfo;
 import de.ids_mannheim.korap.KrillCollection;
 import de.ids_mannheim.korap.index.TextPrependedTokenStream;
 import de.ids_mannheim.korap.util.KrillDate;
-import de.ids_mannheim.korap.util.KrillProperties;
 import de.ids_mannheim.korap.util.QueryException;
-import net.sf.ehcache.Cache;
-import net.sf.ehcache.CacheManager;
-import net.sf.ehcache.Element;
 
 
 /*
@@ -41,17 +32,20 @@
  */
 
 public class CollectionBuilder {
-
-    public final static CacheManager cacheManager = CacheManager.newInstance();
-    public final static Cache cache = cacheManager.getCache("named_vc");
-
-	
     // Logger
     private final static Logger log = LoggerFactory
             .getLogger(KrillCollection.class);
 
     // This advices the java compiler to ignore all loggings
     public static final boolean DEBUG = false;
+    
+    protected IndexInfo indexInfo;
+
+    public CollectionBuilder () {}
+
+    public CollectionBuilder (IndexInfo indexInfo) {
+        this.indexInfo = indexInfo;
+    }
 
 
     public CollectionBuilder.Interface term (String field, String term) {
@@ -138,7 +132,7 @@
     };
 
 	public CollectionBuilder.Interface referTo (String reference) {
-        return new CollectionBuilder.Reference(reference);
+        return new CollectionBuilder.VirtualCorpusReference(reference);
     };
 
 
@@ -275,55 +269,25 @@
     };
 
 
-    public class Reference implements CollectionBuilder.Interface {
+    public class VirtualCorpusReference implements CollectionBuilder.Interface {
         private boolean isNegative = false;
-        private String reference;
-		private Map<Integer, DocBits> docIdMap =
-			new HashMap<Integer, DocBits>();
-
-        public Reference (String reference) {
-            this.reference = reference;
+        private String vcId;
+        private VirtualCorpusReferenceFilter vcRefFilter;
+        
+                
+        public VirtualCorpusReference (String vcId) {
+            this.vcId = vcId;
+            vcRefFilter = new VirtualCorpusReferenceFilter(vcId);
+//            VirtualCorpusCache.setIndexInfo(indexInfo);
         };
 
         public Filter toFilter () throws QueryException {
-            Element element = null;
-            if (KrillCollection.cache != null){
-                element = KrillCollection.cache.get(this.reference);
-            }
-            if (element == null) {
-                if (DEBUG) {
-                    log.debug(reference + " is NOT found in the cache");
-                }
-                KrillCollection kc = new KrillCollection();
-
-				kc.fromStore(this.reference);
-
-				if (kc.hasErrors()) {                    
-                    throw new QueryException(
-						kc.getError(0).getCode(),
-						kc.getError(0).getMessage()
-						);
-				};
-
-				return new ToCacheVCFilter(
-					this.reference,
-					docIdMap,
-					kc.getBuilder(),
-					kc.toFilter()
-					);
-			}
-            else {
-                if (DEBUG) { 
-                    log.debug(reference + " is FOUND in the cache."); 
-                }
-                CachedVCData cc = (CachedVCData) element.getObjectValue();
-                return new CachedVCFilter(this.reference, cc);
-            }
+            return vcRefFilter;
         };
 
 
         public String toString () {
-			return "referTo(" + this.reference + ")";
+			return "referTo(" + this.vcId + ")";
         };
 
 
@@ -336,37 +300,6 @@
             this.isNegative = true;
             return this;
         };
-
-		private String loadVCFile (String ref) {
-			Properties prop = KrillProperties.loadDefaultProperties();
-			if (prop == null){
-				/*
-				  this.addError(StatusCodes.MISSING_KRILL_PROPERTIES,
-							  "krill.properties is not found.");
-				*/
-				return null;
-			}
-			
-			String namedVCPath = prop.getProperty("krill.namedVC");
-			if (!namedVCPath.endsWith("/")){
-				namedVCPath += "/";
-			}
-			File file = new File(namedVCPath+ref+".jsonld");
-			
-			String json = null;
-			try {
-				FileInputStream fis = new FileInputStream(file);
-				json = IOUtils.toString(fis);
-			}
-			catch (IOException e) {
-				/*
-				this.addError(StatusCodes.MISSING_COLLECTION,
-							  "Collection is not found.");
-				*/
-				return null;
-			}
-			return json;
-		}	
     };
 	
 	
@@ -494,82 +427,4 @@
             return this;
         };
     };
-    
-    /** Builder for virtual corpus / collection existing in the cache
-     * 
-     * @author margaretha
-     *
-     */
-    public class CachedVC implements CollectionBuilder.Interface {
-
-        private String cacheKey;
-        private CachedVCData cachedCollection;
-        private boolean isNegative = false;
-
-        public CachedVC (String vcRef, CachedVCData cc) {
-            this.cacheKey = vcRef;
-			this.cachedCollection = cc;
-        }
-
-        @Override
-        public Filter toFilter () {
-            return new CachedVCFilter(this.cacheKey, cachedCollection);
-        }
-
-        @Override
-        public boolean isNegative () {
-            return this.isNegative;
-        }
-
-        @Override
-        public CollectionBuilder.Interface not () {
-            this.isNegative = true;
-            return this;
-        }
-        
-    }
-    
-    /** Wraps a sub CollectionBuilder.Interface to allows VC caching
-     *  
-     * @author margaretha
-     *
-     */
-    public class ToCacheVC implements CollectionBuilder.Interface {
-
-        private CollectionBuilder.Interface child;
-        private String cacheKey;
-        
-        private Map<Integer, DocBits> docIdMap;
-
-        public ToCacheVC (String vcRef, Interface cbi) {
-            this.child = cbi;
-            this.cacheKey = vcRef;
-            this.docIdMap  = new HashMap<Integer, DocBits>();
-        }
-
-        @Override
-        public Filter toFilter () throws QueryException {
-            return new ToCacheVCFilter(cacheKey,docIdMap, child, child.toFilter());
-        }
-
-        @Override
-        public boolean isNegative () {
-            return child.isNegative();
-        }
-
-        @Override
-        public CollectionBuilder.Interface not () {
-            // not supported
-            return this;
-        }
-    }
-
-	// Maybe irrelevant
-    public Interface namedVC (String vcRef, CachedVCData cc) {
-        return new CollectionBuilder.CachedVC(vcRef, cc);
-    }
-    
-    public Interface toCacheVC (String vcRef, Interface cbi) {
-        return new CollectionBuilder.ToCacheVC(vcRef, cbi);
-    }
 };
diff --git a/src/main/java/de/ids_mannheim/korap/collection/ToCacheVCFilter.java b/src/main/java/de/ids_mannheim/korap/collection/ToCacheVCFilter.java
deleted file mode 100644
index 072e1dc..0000000
--- a/src/main/java/de/ids_mannheim/korap/collection/ToCacheVCFilter.java
+++ /dev/null
@@ -1,93 +0,0 @@
-package de.ids_mannheim.korap.collection;
-
-import java.io.IOException;
-import java.util.HashMap;
-import java.util.Map;
-
-import org.apache.lucene.index.LeafReader;
-import org.apache.lucene.index.LeafReaderContext;
-import org.apache.lucene.search.DocIdSet;
-import org.apache.lucene.search.Filter;
-import org.apache.lucene.util.Bits;
-import org.apache.lucene.util.FixedBitSet;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-import de.ids_mannheim.korap.KrillCollection;
-import de.ids_mannheim.korap.collection.CollectionBuilder.Interface;
-import net.sf.ehcache.Element;
-
-/**
- * Filter for virtual corpus / collection that should be cached.
- * 
- * @author margaretha
- *
- */
-public class ToCacheVCFilter extends Filter {
-    private Filter filter;
-    private CollectionBuilder.Interface cbi;
-    private String cacheKey;
-    private Map<Integer, DocBits> docIdMap;
-    // EM: auto caching is disabled regarding issue #44 
-    private boolean isAutoCachingEnabled = false;
-
-    public final static Logger log = LoggerFactory.getLogger(ToCacheVCFilter.class);
-    public static final boolean DEBUG = false;
-            
-    public ToCacheVCFilter (String cacheKey, Map<Integer, DocBits> docIdMap,
-                            Interface cbi, Filter filter) {
-        this.cacheKey = cacheKey;
-        this.docIdMap = docIdMap;
-        this.cbi = cbi;
-        this.filter = filter;
-    }
-
-    @Override
-    public DocIdSet getDocIdSet (LeafReaderContext context, Bits acceptDocs)
-            throws IOException {
-
-        DocIdSet docIdSet = filter.getDocIdSet(context, acceptDocs);
-
-        final LeafReader reader = context.reader();
-        int maxDoc = reader.maxDoc();
-        FixedBitSet bitset = new FixedBitSet(maxDoc);
-
-        if (docIdSet == null) {
-            if (cbi.isNegative()) {
-                bitset.set(0, maxDoc);
-            }
-            else {
-                bitset.clear(0, maxDoc);
-            }
-        }
-        else {
-            bitset.or(docIdSet.iterator());
-            if (cbi.isNegative()) {
-                bitset.flip(0, maxDoc);
-            }
-        }
-
-        if (isAutoCachingEnabled) {
-            docIdMap.put(context.hashCode(),
-                    new DocBits(bitset.getBits(), bitset.length()));
-            CachedVCData cachedVCData =
-                    new CachedVCData(new HashMap<>(docIdMap));
-
-            if (KrillCollection.cache == null){
-                KrillCollection.initializeCache();
-            }
-            KrillCollection.cache.remove(cacheKey);
-            KrillCollection.cache.put(new Element(cacheKey, cachedVCData));
-        }
-
-        if (DEBUG){
-            log.debug("To cache doc bits length: "+ docIdSet.bits().length());
-        }
-        return docIdSet;
-    }
-
-    @Override
-    public String toString () {
-        return "referTo(" + this.cacheKey + ")";
-    };
-}
diff --git a/src/main/java/de/ids_mannheim/korap/collection/VirtualCorpusReferenceFilter.java b/src/main/java/de/ids_mannheim/korap/collection/VirtualCorpusReferenceFilter.java
new file mode 100644
index 0000000..2ee60bd
--- /dev/null
+++ b/src/main/java/de/ids_mannheim/korap/collection/VirtualCorpusReferenceFilter.java
@@ -0,0 +1,104 @@
+package de.ids_mannheim.korap.collection;
+
+import java.io.IOException;
+
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.search.DocIdSet;
+import org.apache.lucene.search.Filter;
+import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.FixedBitSet;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import de.ids_mannheim.korap.KrillCollection;
+import de.ids_mannheim.korap.cache.VirtualCorpusCache;
+import de.ids_mannheim.korap.util.Fingerprinter;
+import de.ids_mannheim.korap.util.QueryException;
+
+public class VirtualCorpusReferenceFilter extends Filter {
+
+    public final static Logger log = LoggerFactory
+            .getLogger(VirtualCorpusReferenceFilter.class);
+    public static boolean DEBUG = false;
+
+    private String vcId;
+    private DocBitsSupplier docBitsSupplier;
+
+    public VirtualCorpusReferenceFilter (String vcId) {
+        this.vcId = vcId;
+        docBitsSupplier = new DocBitsSupplier();
+    }
+
+
+    @Override
+    public DocIdSet getDocIdSet (LeafReaderContext context, Bits acceptDocs)
+            throws IOException {
+        String leafFingerprint = Fingerprinter.create(
+                context.reader().getCombinedCoreAndDeletesKey().toString());
+        
+        DocBits docBits = VirtualCorpusCache.getDocBits(vcId, leafFingerprint,
+                () -> {
+                    try {
+                        return docBitsSupplier.supplyDocBits(context, acceptDocs);
+                    }
+                    catch (IOException | QueryException e) {
+                        throw new RuntimeException(e);
+                    }
+                });
+        return docBits.createBitDocIdSet();
+    }
+
+    public class DocBitsSupplier {
+
+        private Filter filter;
+        private CollectionBuilder.Interface cbi;
+        
+        public DocBitsSupplier () {}
+        
+        public DocBits supplyDocBits (LeafReaderContext context,
+                Bits acceptDocs) throws IOException, QueryException {
+            if (cbi == null || filter == null) {
+                KrillCollection kc = new KrillCollection();
+                // load from file
+                kc.fromStore(vcId);
+                if (kc.hasErrors()) {
+                    throw new QueryException(kc.getError(0).getCode(),
+                            kc.getError(0).getMessage());
+                }
+
+                this.cbi = kc.getBuilder();
+                this.filter = kc.toFilter();
+            }
+                
+            DocIdSet docIdSet = filter.getDocIdSet(context, acceptDocs);
+            return calculateDocBits(docIdSet, context.reader().maxDoc());
+        }
+
+
+        private DocBits calculateDocBits (DocIdSet docIdSet, int maxDoc)
+                throws IOException {
+            FixedBitSet bitset = new FixedBitSet(maxDoc);
+            if (docIdSet == null) {
+                if (cbi.isNegative()) {
+                    bitset.set(0, maxDoc);
+                }
+                else {
+                    bitset.clear(0, maxDoc);
+                }
+            }
+            else {
+                bitset.or(docIdSet.iterator());
+                if (cbi.isNegative()) {
+                    bitset.flip(0, maxDoc);
+                }
+            }
+
+            return new DocBits(bitset.getBits(), bitset.length());
+        }
+    }
+    
+    @Override
+    public String toString () {
+        return "VirtualCorpusReferenceFilter("+vcId+")";
+    }
+}
diff --git a/src/main/java/de/ids_mannheim/korap/util/Fingerprinter.java b/src/main/java/de/ids_mannheim/korap/util/Fingerprinter.java
new file mode 100644
index 0000000..59113c3
--- /dev/null
+++ b/src/main/java/de/ids_mannheim/korap/util/Fingerprinter.java
@@ -0,0 +1,32 @@
+package de.ids_mannheim.korap.util;
+
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.Base64;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class Fingerprinter {
+
+    private final static Logger log = LoggerFactory
+            .getLogger(Fingerprinter.class);
+
+    private static MessageDigest md;
+
+    public static String create (String key) {
+        try {
+            md = MessageDigest.getInstance("MD5");
+        }
+        catch (NoSuchAlgorithmException e) {
+            log.error(e.getMessage());
+            return e.getMessage();
+        };
+
+        md.update(key.getBytes());
+        String code = new String(Base64.getEncoder().encode(md.digest()));
+        md.reset();
+        return code;
+
+    }
+}
diff --git a/src/test/java/de/ids_mannheim/korap/cache/TestCache.java b/src/test/java/de/ids_mannheim/korap/cache/TestCache.java
index 06a882d..857765a 100644
--- a/src/test/java/de/ids_mannheim/korap/cache/TestCache.java
+++ b/src/test/java/de/ids_mannheim/korap/cache/TestCache.java
@@ -1,18 +1,18 @@
 package de.ids_mannheim.korap.cache;
 
+import static org.junit.Assert.assertEquals;
+
 import java.util.Collections;
 
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
 import net.sf.jsr107cache.Cache;
 import net.sf.jsr107cache.CacheException;
 import net.sf.jsr107cache.CacheFactory;
 import net.sf.jsr107cache.CacheManager;
 
-import static org.junit.Assert.*;
-import org.junit.Test;
-import org.junit.Ignore;
-import org.junit.runner.RunWith;
-import org.junit.runners.JUnit4;
-
 @RunWith(JUnit4.class)
 public class TestCache {
 
diff --git a/src/test/java/de/ids_mannheim/korap/cache/TestVirtualCorpusCache.java b/src/test/java/de/ids_mannheim/korap/cache/TestVirtualCorpusCache.java
new file mode 100644
index 0000000..bd65ab2
--- /dev/null
+++ b/src/test/java/de/ids_mannheim/korap/cache/TestVirtualCorpusCache.java
@@ -0,0 +1,130 @@
+package de.ids_mannheim.korap.cache;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Map;
+
+import org.apache.commons.io.IOUtils;
+import org.junit.Test;
+
+import de.ids_mannheim.korap.Krill;
+import de.ids_mannheim.korap.KrillIndex;
+import de.ids_mannheim.korap.collection.DocBits;
+import de.ids_mannheim.korap.response.Result;
+import de.ids_mannheim.korap.util.QueryException;
+
+public class TestVirtualCorpusCache {
+
+    private KrillIndex ki;
+    private String queryRefJson;
+
+    public TestVirtualCorpusCache () throws IOException {
+        ki = createIndex();
+
+        String file = "/queries/collections/vc-ref/query-with-vc-ref.jsonld";
+        InputStream is = getClass().getResourceAsStream(file);
+        queryRefJson = IOUtils.toString(is, "utf-8");
+    }
+
+
+    private KrillIndex createIndex () throws IOException {
+        KrillIndex ki = new KrillIndex();
+        String[] docIds = new String[] { "00001", "00002", "00003" };
+        int uid = 1;
+        for (String i : docIds) {
+            ki.addDoc(uid++,
+                    getClass().getResourceAsStream("/wiki/" + i + ".json.gz"),
+                    true);
+        }
+        ki.commit();
+
+        ki.addDoc(uid++, getClass().getResourceAsStream("/wiki/00004.json.gz"),
+                true);
+        ki.commit();
+        return ki;
+    }
+
+
+    @Test
+    public void testStoreUncachedVC () throws IOException, QueryException {
+        String vcId = "named-vc4";
+
+        File f = new File(VirtualCorpusCache.CACHE_LOCATION + "/" + vcId);
+        assertFalse(f.exists());
+
+        VirtualCorpusCache.store(vcId, ki);
+        assertTrue(VirtualCorpusCache.contains(vcId));
+
+        Map<String, DocBits> docIdMap = VirtualCorpusCache.retrieve(vcId);
+        assertEquals(2, docIdMap.size());
+
+        VirtualCorpusCache.reset();
+    }
+
+
+    @Test
+    public void testReferToUncachedVC () throws IOException, QueryException {
+        String vcId = "named-vc1";
+        assertFalse(VirtualCorpusCache.contains(vcId));
+
+        Krill krill = new Krill(queryRefJson);
+        Result result = krill.apply(ki);
+        assertEquals(27, result.getTotalResults());
+
+        assertTrue(VirtualCorpusCache.contains(vcId));
+        Map<String, DocBits> vc1 = VirtualCorpusCache.retrieve(vcId);
+        assertNotNull(vc1);
+
+        VirtualCorpusCache.reset();
+    }
+
+
+    @Test
+    public void testUpdateCachedVC () throws IOException {
+        // VC cache will be marked for cleaning up 
+        // because of storing a new VC
+        KrillIndex ki = createIndex();
+        Krill krill = new Krill(queryRefJson);
+        Result result = krill.apply(ki);
+        assertEquals(27, result.getTotalResults());
+
+        assertEquals(2,
+                VirtualCorpusCache.map.get("named-vc1").keySet().size());
+
+        ki.delDoc(2);
+        ki.commit();
+
+        // VC cache will be marked for cleaning up again
+        // because of index change.
+        krill = new Krill(queryRefJson);
+        result = krill.apply(ki);
+        assertEquals(17, result.getTotalResults());
+
+        // The old leaf fingerprint should be cleaned up, thus the map 
+        // should have the same size. But the fingerprints should be 
+        // different from before the 1st cleaning up
+        assertEquals(2,
+                VirtualCorpusCache.map.get("named-vc1").keySet().size());
+
+        // VC cache will be cleaned up for the 2nd time 
+        // resulting the same leaf-fingerprints
+        krill = new Krill(queryRefJson);
+        result = krill.apply(ki);
+        assertEquals(17, result.getTotalResults());
+
+        assertEquals(2,
+                VirtualCorpusCache.map.get("named-vc1").keySet().size());
+
+        ki.close();
+
+        VirtualCorpusCache.reset();
+    }
+
+
+}
diff --git a/src/test/java/de/ids_mannheim/korap/collection/TestCollectionBuilder.java b/src/test/java/de/ids_mannheim/korap/collection/TestCollectionBuilder.java
index 2ee8cb1..9c500f1 100644
--- a/src/test/java/de/ids_mannheim/korap/collection/TestCollectionBuilder.java
+++ b/src/test/java/de/ids_mannheim/korap/collection/TestCollectionBuilder.java
@@ -97,10 +97,8 @@
     public void builderReferenceNested () throws IOException {
         CollectionBuilder kc = new CollectionBuilder();
 
-        // The group can't stringify, because the filtering
-        // phase won't work. This is acceptable.
         assertEquals(
-            "",
+            "OrGroup(VirtualCorpusReferenceFilter(example) opennlp:check)",
             kc.orGroup().with(
                 kc.referTo("example")
                 ).with(
diff --git a/src/test/java/de/ids_mannheim/korap/collection/TestCollectionCache.java b/src/test/java/de/ids_mannheim/korap/collection/TestCollectionCache.java
deleted file mode 100644
index ee3fef4..0000000
--- a/src/test/java/de/ids_mannheim/korap/collection/TestCollectionCache.java
+++ /dev/null
@@ -1,29 +0,0 @@
-package de.ids_mannheim.korap.collection;
-
-import static org.junit.Assert.assertTrue;
-
-import java.io.IOException;
-
-import org.junit.Test;
-
-import de.ids_mannheim.korap.KrillCollection;
-import de.ids_mannheim.korap.KrillIndex;
-import de.ids_mannheim.korap.index.FieldDocument;
-import net.sf.ehcache.Cache;
-
-public class TestCollectionCache {
-
-    @Test
-    public void testNullCache() throws IOException{
-        KrillCollection kc = new KrillCollection();
-        Cache temp = KrillCollection.cache;
-        assertTrue(KrillCollection.cache != null);
-        
-        KrillCollection.cache = null;
-        KrillIndex ki = new KrillIndex();
-        ki.addDoc(new FieldDocument());
-        ki.commit();
-        
-        KrillCollection.cache = temp;
-    }
-}
diff --git a/src/test/java/de/ids_mannheim/korap/collection/TestKrillCollectionIndex.java b/src/test/java/de/ids_mannheim/korap/collection/TestKrillCollectionIndex.java
index 69e8d9f..7e80ba2 100644
--- a/src/test/java/de/ids_mannheim/korap/collection/TestKrillCollectionIndex.java
+++ b/src/test/java/de/ids_mannheim/korap/collection/TestKrillCollectionIndex.java
@@ -2,17 +2,13 @@
 
 import static de.ids_mannheim.korap.TestSimple.getJsonString;
 import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 
 import java.io.IOException;
-import java.util.Properties;
 
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.spans.SpanQuery;
 import org.apache.lucene.search.spans.SpanTermQuery;
-import org.junit.Ignore;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -24,10 +20,7 @@
 import de.ids_mannheim.korap.query.QueryBuilder;
 import de.ids_mannheim.korap.response.Result;
 import de.ids_mannheim.korap.response.SearchContext;
-import de.ids_mannheim.korap.util.KrillProperties;
-import de.ids_mannheim.korap.util.QueryException;
 import de.ids_mannheim.korap.util.StatusCodes;
-import net.sf.ehcache.Element;
 
 
 @RunWith(JUnit4.class)
@@ -621,13 +614,12 @@
 
 		// This test was adopted from TestVCCaching,
 		// But does not fail anymore for deserialization
-        String json = _getJSONString("unknown-vc-ref.jsonld");
+        String json = _getJSONString("vc-ref/unknown-vc-ref.jsonld");
 
         KrillCollection kc = new KrillCollection(json);
 		assertEquals("referTo(https://korap.ids-mannheim.de/@ndiewald/MyCorpus)", kc.getBuilder().toString());
 
-		// Fails on filtering
-		assertEquals("", kc.toString());
+		assertEquals("VirtualCorpusReferenceFilter(https://korap.ids-mannheim.de/@ndiewald/MyCorpus)",kc.toString());
 		
         QueryBuilder kq = new QueryBuilder("field");
 		
@@ -637,433 +629,10 @@
 		Result result = krill.apply(ki);
 
 		assertEquals(StatusCodes.MISSING_COLLECTION, result.getError(0).getCode());
+		assertTrue(result.getError(0).getMessage().startsWith("Collection is not found"));
 	};
 
     @Test
-    @Ignore
-    public void testCache () throws IOException {
-
-		Properties prop = KrillProperties.loadDefaultProperties();
-
-		String vcPath = getClass().getResource(path + "named-vcs").getFile();
-		String tempVC = prop.getProperty("krill.namedVC");
-		prop.setProperty("krill.namedVC", vcPath);
-
-		ki = new KrillIndex();
-		ki.addDoc(createDoc1());
-		ki.addDoc(createDoc2());
-		ki.commit();
-		
-        testManualAddToCache(ki, "named-vcs/named-vc1.jsonld", "named-vc1");
-        testManualAddToCache(ki, "named-vcs/named-vc2.jsonld", "named-vc2");
-        
-        Element element = KrillCollection.cache.get("named-vc1");
-        CachedVCData cc = (CachedVCData) element.getObjectValue();
-        assertTrue(cc.getDocIdMap().size() > 0);
-
-        element = KrillCollection.cache.get("named-vc2");
-        cc = (CachedVCData) element.getObjectValue();
-        assertTrue(cc.getDocIdMap().size() > 0);
-
-		// Check for cache location
-        assertFalse(KrillCollection.cache.isElementInMemory("named-vc1"));
-        assertTrue(KrillCollection.cache.isElementOnDisk("named-vc1"));
-        assertTrue(KrillCollection.cache.isElementInMemory("named-vc2"));
-        assertTrue(KrillCollection.cache.isElementOnDisk("named-vc2"));
-
-        // testSearchCachedVC();
-		String json = _getJSONString("query-with-vc-ref.jsonld");
-		// references named-vc1: ID eq ["doc-2","doc-3"]
-
-		Krill krill = new Krill(json);
-		// TODO: Better keep the reference
-		testManualAddToCache(ki, "named-vcs/named-vc1.jsonld", "named-vc1");
-		assertEquals("referTo(cached:named-vc1)", krill.getCollection().toString());
-
-		Result result = krill.apply(ki);
-		assertEquals("[[a]] c d", result.getMatch(0).getSnippetBrackets());
-		assertEquals(result.getMatch(0).getUID(), 2);
-		assertEquals(result.getMatches().size(), 1);
-		
-        // testAddDocToIndex();
-		ki.addDoc(createDoc3());
-		ki.commit();
-
-		// Cache is removed after index change
-        element = KrillCollection.cache.get("named-vc1");
-        assertNull(element);
-
-		// Restart search - this time it's not precached
-        krill = new Krill(json);
-		assertEquals("referTo(named-vc1)", krill.getCollection().toString());
-		result = krill.apply(ki);
-
-		assertEquals("[[a]] c d", result.getMatch(0).getSnippetBrackets());
-		assertEquals("[[a]] d e", result.getMatch(1).getSnippetBrackets());
-		assertEquals(result.getMatches().size(), 2);
-
-		// testAutoCachingMatch
-		// Check autocache
-		element = KrillCollection.cache.get("named-vc1");
-		cc = (CachedVCData) element.getObjectValue();
-        assertTrue(cc.getDocIdMap().size() > 0);
-		
-		// Because of autocaching, this should work now
-        krill = new Krill(json);
-		assertEquals("referTo(cached:named-vc1)", krill.getCollection().toString());
-		result = krill.apply(ki);
-		assertEquals("[[a]] c d", result.getMatch(0).getSnippetBrackets());
-		assertEquals("[[a]] d e", result.getMatch(1).getSnippetBrackets());
-		assertEquals(result.getMatches().size(), 2);
-
-		// Cache is removed on deletion
-		ki.addDoc(createDoc1());
-		ki.commit();
-
-		// Check cache
-		element = KrillCollection.cache.get("named-vc1");
-        assertNull(element);
-
-		// Rerun query
-        krill = new Krill(json);
-		assertEquals("referTo(named-vc1)", krill.getCollection().toString());
-		result = krill.apply(ki);
-		assertEquals("[[a]] c d", result.getMatch(0).getSnippetBrackets());
-		assertEquals("[[a]] d e", result.getMatch(1).getSnippetBrackets());
-		assertEquals(result.getMatches().size(), 2);
-		
-		// testClearCache
-		KrillCollection.cache.removeAll();
-
-        element = KrillCollection.cache.get("named-vc1");
-        assertNull(element);
-
-		prop.setProperty("krill.namedVC", tempVC);
-    };
-
-	@Test
-	@Ignore
-    public void testNestedNamedVCs () throws IOException {
-	    KrillCollection.initializeCache();
-	    
-        Properties prop = KrillProperties.loadDefaultProperties();
-
-        String vcPath = getClass().getResource(path + "named-vcs").getFile();
-        String tempVC = prop.getProperty("krill.namedVC");
-        prop.setProperty("krill.namedVC", vcPath);
-        
-        ki = new KrillIndex();
-        ki.addDoc(createDoc1());
-        ki.addDoc(createDoc2());
-        ki.addDoc(createDoc3());
-        ki.commit();
-
-        // Check cache
-        Element element = KrillCollection.cache.get("named-vc1");
-        assertNull(element);
-
-        element = KrillCollection.cache.get("named-vc2");
-        assertNull(element);
-
-        QueryBuilder kq = new QueryBuilder("tokens");
-        KrillCollection kc = new KrillCollection(ki);
-        CollectionBuilder cb = kc.build();
-        Krill krill = new Krill(kq.seg("i:a"));
-
-        kc.fromBuilder(
-            cb.orGroup().with(
-                cb.referTo("named-vc1")
-                ).with(
-                    cb.referTo("named-vc2")
-                    )
-            );
-        krill.setCollection(kc);
-        // named-vc1: UID:[2,3]
-        // named-vc2: author:Frank (doc-1)
-
-        assertEquals("OrGroup(referTo(named-vc1) referTo(named-vc2))",
-                     krill.getCollection().toString());
-
-        assertEquals("tokens:i:a", krill.getSpanQuery().toString());
-        
-        Result result = krill.apply(ki);
-        assertEquals("[[a]] b c", result.getMatch(0).getSnippetBrackets());
-        assertEquals("[[a]] c d", result.getMatch(1).getSnippetBrackets());
-        assertEquals("[[a]] d e", result.getMatch(2).getSnippetBrackets());
-        assertEquals(3, result.getMatches().size());
-
-        element = KrillCollection.cache.get("named-vc2");
-        CachedVCData cc = (CachedVCData) element.getObjectValue();
-        assertTrue(cc.getDocIdMap().size() > 0);
-        
-        kc.fromBuilder(
-            cb.orGroup().with(
-                cb.referTo("named-vc1")
-                ).with(
-                    cb.referTo("named-vc2")
-                    )
-            );
-        
-        assertEquals("OrGroup(referTo(cached:named-vc1) referTo(cached:named-vc2))",
-                     krill.getCollection().toString());
-
-        result = krill.apply(ki);
-        assertEquals("[[a]] b c", result.getMatch(0).getSnippetBrackets());
-        assertEquals("[[a]] c d", result.getMatch(1).getSnippetBrackets());
-        assertEquals("[[a]] d e", result.getMatch(2).getSnippetBrackets());
-        assertEquals(3, result.getMatches().size());
-
-        kc.fromBuilder(
-            cb.orGroup().with(
-                cb.referTo("named-vc1")
-                ).with(
-                    cb.referTo("named-vc2")
-                    )
-            );
-        
-        assertEquals("OrGroup(referTo(cached:named-vc1) referTo(cached:named-vc2))",
-                     krill.getCollection().toString());
-
-        result = krill.apply(ki);
-        assertEquals("[[a]] b c", result.getMatch(0).getSnippetBrackets());
-        assertEquals("[[a]] c d", result.getMatch(1).getSnippetBrackets());
-        assertEquals("[[a]] d e", result.getMatch(2).getSnippetBrackets());
-        assertEquals(3, result.getMatches().size());
-
-        kc.fromBuilder(cb.referTo("named-vc1"));
-        
-        assertEquals("referTo(cached:named-vc1)",
-                     krill.getCollection().toString());
-
-        result = krill.apply(ki);
-        assertEquals("[[a]] c d", result.getMatch(0).getSnippetBrackets());
-        assertEquals("[[a]] d e", result.getMatch(1).getSnippetBrackets());
-        assertEquals(2, result.getMatches().size());
-
-
-        kc.fromBuilder(cb.referTo("named-vc2"));
-        
-        assertEquals("referTo(cached:named-vc2)",
-                     krill.getCollection().toString());
-
-        result = krill.apply(ki);
-        assertEquals("[[a]] b c", result.getMatch(0).getSnippetBrackets());
-        assertEquals(1, result.getMatches().size());
-        
-        prop.setProperty("krill.namedVC", tempVC);
-    };
-
-
-	@Test
-	@Ignore
-    public void testNamedVCsAfterQueryWithMissingDocs () throws IOException {
-	    KrillCollection.initializeCache();
-        Properties prop = KrillProperties.loadDefaultProperties();
-
-        String vcPath = getClass().getResource(path + "named-vcs").getFile();
-        String tempVC = prop.getProperty("krill.namedVC");
-        prop.setProperty("krill.namedVC", vcPath);
-        
-        ki = new KrillIndex();
-        ki.addDoc(createDoc1());
-        ki.commit();
-        ki.addDoc(createDoc2());
-        ki.commit();
-        ki.addDoc(createDoc3());
-        ki.commit();
-
-        // Check cache
-        Element element = KrillCollection.cache.get("named-vc1");
-        assertNull(element);
-
-        element = KrillCollection.cache.get("named-vc2");
-        assertNull(element);
-
-        QueryBuilder kq = new QueryBuilder("tokens");
-        KrillCollection kc = new KrillCollection(ki);
-        CollectionBuilder cb = kc.build();
-
-        // Check only for c and cache
-        Krill krill = new Krill(kq.seg("i:c"));
-
-        kc.fromBuilder(
-            cb.orGroup().with(
-                cb.referTo("named-vc1")
-                ).with(
-                    cb.referTo("named-vc2")
-                    )
-            );
-        krill.setCollection(kc);
-        // named-vc1: UID:[2,3]
-        // named-vc2: author:Frank (doc-1)
-
-        assertEquals("OrGroup(referTo(named-vc1) referTo(named-vc2))",
-                     krill.getCollection().toString());
-
-        assertEquals("tokens:i:c", krill.getSpanQuery().toString());
-        
-        Result result = krill.apply(ki);
-        assertEquals("a b [[c]]", result.getMatch(0).getSnippetBrackets());
-        assertEquals("a [[c]] d", result.getMatch(1).getSnippetBrackets());
-        assertEquals(2, result.getMatches().size());
-
-        element = KrillCollection.cache.get("named-vc2");
-        CachedVCData cc = (CachedVCData) element.getObjectValue();
-        assertTrue(cc.getDocIdMap().size() > 0);
-        
-        kc.fromBuilder(
-            cb.orGroup().with(
-                cb.referTo("named-vc1")
-                ).with(
-                    cb.referTo("named-vc2")
-                    )
-            );
-        
-        assertEquals("OrGroup(referTo(cached:named-vc1) referTo(cached:named-vc2))",
-                     krill.getCollection().toString());
-
-        // Check again for c with cache
-        result = krill.apply(ki);
-        assertEquals("a b [[c]]", result.getMatch(0).getSnippetBrackets());
-        assertEquals("a [[c]] d", result.getMatch(1).getSnippetBrackets());
-        assertEquals(2, result.getMatches().size());
-
-        // Check for a with cache
-        krill = new Krill(kq.seg("i:a"));
-        krill.setCollection(kc);
-
-        assertEquals("OrGroup(referTo(cached:named-vc1) referTo(cached:named-vc2))",
-                     krill.getCollection().toString());
-
-        // Check again for c with cache
-        result = krill.apply(ki);
-        assertEquals("[[a]] b c", result.getMatch(0).getSnippetBrackets());
-        assertEquals("[[a]] c d", result.getMatch(1).getSnippetBrackets());
-        assertEquals("[[a]] d e", result.getMatch(2).getSnippetBrackets());
-        assertEquals(3, result.getMatches().size());
-                
-        prop.setProperty("krill.namedVC", tempVC);
-    };
-
-
-	@Ignore
-    public void testNamedVCsAfterCorpusWithMissingDocs () throws IOException {
-        Properties prop = KrillProperties.loadDefaultProperties();
-
-        String vcPath = getClass().getResource(path + "named-vcs").getFile();
-        String tempVC = prop.getProperty("krill.namedVC");
-        prop.setProperty("krill.namedVC", vcPath);
-        
-        ki = new KrillIndex();
-        ki.addDoc(createDoc1());
-        ki.commit();
-        ki.addDoc(createDoc2());
-        ki.commit();
-        ki.addDoc(createDoc3());
-        ki.commit();
-
-        // Check cache
-        Element element = KrillCollection.cache.get("named-vc1");
-        assertNull(element);
-
-        element = KrillCollection.cache.get("named-vc2");
-        assertNull(element);
-
-        QueryBuilder kq = new QueryBuilder("tokens");
-        KrillCollection kc = new KrillCollection(ki);
-        CollectionBuilder cb = kc.build();
-
-        // Check only for c and cache
-        Krill krill = new Krill(kq.seg("i:a"));
-
-        kc.fromBuilder(
-            cb.andGroup().with(
-                cb.term("textClass","kultur")
-                ).with(
-                    cb.orGroup().with(
-                        cb.referTo("named-vc1")
-                        ).with(
-                            cb.referTo("named-vc2")
-                            )
-                    )
-            );
-        krill.setCollection(kc);
-        // named-vc1: UID:[2,3]
-        // named-vc2: author:Frank (doc-1)
-        // textClass:kultur (doc-1,doc-2)
-
-        assertEquals(
-            "AndGroup(textClass:kultur OrGroup(referTo(named-vc1) referTo(named-vc2)))",
-            krill.getCollection().toString());
-        
-        assertEquals("tokens:i:a", krill.getSpanQuery().toString());
-        
-        Result result = krill.apply(ki);
-        assertEquals("[[a]] b c", result.getMatch(0).getSnippetBrackets());
-        assertEquals("[[a]] c d", result.getMatch(1).getSnippetBrackets());
-        assertEquals(2, result.getMatches().size());
-
-        element = KrillCollection.cache.get("named-vc1");
-        CachedVCData cc = (CachedVCData) element.getObjectValue();
-        assertTrue(cc.getDocIdMap().size() > 0);
-
-        element = KrillCollection.cache.get("named-vc2");
-        cc = (CachedVCData) element.getObjectValue();
-        assertTrue(cc.getDocIdMap().size() > 0);
-
-        kc.fromBuilder(
-            cb.orGroup().with(
-                cb.referTo("named-vc1")
-                ).with(
-                    cb.referTo("named-vc2")
-                    )
-            );
-        
-        assertEquals("OrGroup(referTo(cached:named-vc1) referTo(cached:named-vc2))",
-                     krill.getCollection().toString());
-
-        // Check again for c with cache
-        result = krill.apply(ki);
-		assertEquals("[[a]] b c", result.getMatch(0).getSnippetBrackets());
-        assertEquals("[[a]] c d", result.getMatch(1).getSnippetBrackets());
-        assertEquals("[[a]] d e", result.getMatch(2).getSnippetBrackets());
-        assertEquals(3, result.getMatches().size());
-
-        prop.setProperty("krill.namedVC", tempVC);
-    };
-    
-    @Test
-    public void testCollectionWithVCRefAndPubDate () throws IOException {
-
-        KrillCollection.initializeCache();
-
-        ki = new KrillIndex();
-        ki.addDoc(createDoc2());
-        ki.addDoc(createDoc3());
-        ki.addDoc(createDoc5000());
-        ki.commit();
-
-        testManualAddToCache(ki, "named-vcs/named-vc3.jsonld", "named-vc3");
-
-        Element element = KrillCollection.cache.get("named-vc3");
-        CachedVCData cc = (CachedVCData) element.getObjectValue();
-        assertTrue(cc.getDocIdMap().size() > 0);
-            
-        String json = _getJSONString("collection-with-vc-ref-and-pubDate.jsonld");
-
-        KrillCollection kc = new KrillCollection(json);
-        kc.setIndex(ki);
-        assertEquals(2, kc.numberOf("documents"));
-        
-        // testAddDocToIndex();
-        ki.addDoc(createDoc1());
-        ki.commit();
-        // Cache is removed after index change
-
-    }
-    
-
-    @Test
     public void filterExampleFromLegacy () throws Exception {
 
         // Construct index
@@ -1654,20 +1223,6 @@
         return fd;
     };
 
-    
-    private void testManualAddToCache (KrillIndex index, String filename, String vcName) throws IOException {
-		String json = _getJSONString(filename);
-
-        KrillCollection kc = new KrillCollection(json);
-        kc.setIndex(index);
-		try {
-			kc.storeInCache(vcName);
-		}
-		catch (QueryException qe) {
-			System.err.println(qe.getLocalizedMessage());
-		};
-    };
-
     private String _getJSONString (String file) {
         return getJsonString(getClass().getResource(path + file).getFile());
     };
diff --git a/src/test/resources/krill.properties b/src/test/resources/krill.properties
index ea60670..eb7f374 100644
--- a/src/test/resources/krill.properties
+++ b/src/test/resources/krill.properties
@@ -2,4 +2,6 @@
 krill.name = ${project.name}
 krill.indexDir = test-output
 krill.namedVC = vc
-krill.index.commit.count = 15
\ No newline at end of file
+krill.index.commit.count = 15
+
+krill.namedVC=src/test/resources/queries/collections/named-vcs/
\ No newline at end of file
diff --git a/src/test/resources/queries/collections/named-vcs/named-vc4.jsonld b/src/test/resources/queries/collections/named-vcs/named-vc4.jsonld
new file mode 100644
index 0000000..7f19bb0
--- /dev/null
+++ b/src/test/resources/queries/collections/named-vcs/named-vc4.jsonld
@@ -0,0 +1,11 @@
+{"collection": {
+    "@type": "koral:doc",
+    "key": "textSigle",
+    "match": "match:eq",
+    "type" : "type:string",
+    "value": [
+          "WPD/AAA/00001",
+          "WPD/AAA/00002",
+          "WPD/AAA/00003"
+    ]
+}}
diff --git a/src/test/resources/queries/collections/query-with-vc-ref.jsonld b/src/test/resources/queries/collections/vc-ref/query-with-vc-ref.jsonld
similarity index 91%
rename from src/test/resources/queries/collections/query-with-vc-ref.jsonld
rename to src/test/resources/queries/collections/vc-ref/query-with-vc-ref.jsonld
index 86547ac..40d2c2c 100644
--- a/src/test/resources/queries/collections/query-with-vc-ref.jsonld
+++ b/src/test/resources/queries/collections/vc-ref/query-with-vc-ref.jsonld
@@ -3,7 +3,7 @@
     "wrap":{
       "@type":"koral:term",
       "layer":"orth",
-      "key":"a",
+      "key":"der",
       "match":"match:eq"
     }
   },
diff --git a/src/test/resources/queries/collections/unknown-vc-ref.jsonld b/src/test/resources/queries/collections/vc-ref/unknown-vc-ref.jsonld
similarity index 100%
rename from src/test/resources/queries/collections/unknown-vc-ref.jsonld
rename to src/test/resources/queries/collections/vc-ref/unknown-vc-ref.jsonld