Update to Java 21

Change-Id: Icb040ee1c8c90abce44c5884d97a2c1a0b082ff8
Reviewed-on: https://korap.ids-mannheim.de/gerrit/c/KorAP/Koral/+/10084
Reviewed-by: margaretha <margaretha@ids-mannheim.de>
Reviewed-by: Nils Diewald <nils@diewald-online.de>
Reviewed-by: Marc Kupietz <kupietz@ids-mannheim.de>
diff --git a/Changes b/Changes
index f79eb55..07571a5 100644
--- a/Changes
+++ b/Changes
@@ -1,3 +1,6 @@
+0.48 2025-11-17
+     - [security] Update to Java 21.
+
 0.47 2025-10-16
 	- [enhancement] Add apiVersion for QuerySerializer, CorpusQuery-, 
 	  Poliqarp- and CQP processors.
diff --git a/README.md b/README.md
index 280ea32..c098865 100644
--- a/README.md
+++ b/README.md
@@ -118,7 +118,7 @@
 
 ## Prerequisites
 
-* Java 11 (OpenJDK or Oracle JDK with JCE)
+* Java 21 (OpenJDK or Oracle JDK with JCE)
 * [Git](http://git-scm.com/)
 * At least [Maven 3.2.1](https://maven.apache.org/)
 * Further dependencies are resolved by Maven.
diff --git a/pom.xml b/pom.xml
index 5080c61..423ac42 100644
--- a/pom.xml
+++ b/pom.xml
@@ -4,7 +4,7 @@
 
 	<groupId>de.ids-mannheim.korap.koral</groupId>
 	<artifactId>Koral</artifactId>
-	<version>0.47</version>
+	<version>0.48</version>
 	<packaging>jar</packaging>
 	<name>Koral</name>
 	<url>https://korap.ids-mannheim.de</url>
@@ -42,7 +42,7 @@
 		<jackson.version>2.19.2</jackson.version>
 		<antlr4.version>4.9.3</antlr4.version>
 		<antlr3.version>3.5.3</antlr3.version>
-		<java.version>17</java.version>
+		<java.version>21</java.version>
 		<log4j.version>2.25.2</log4j.version>
 	</properties>