diff --git a/README.md b/README.md
index 3984034..06cc3c5 100644
--- a/README.md
+++ b/README.md
@@ -93,7 +93,7 @@ passing an array of `$options` in the constructor:
   **Type**: `string`
   **Default**: `Cache-Tags`
 
-### Cache Tagging
+### Cache tagging
 
 Tag cache entries by adding a response header with the tags as a comma 
 separated value. By default, that header is called `Cache-Tags`, this can be
@@ -103,6 +103,20 @@ To invalidate tags, call the method `Psr6Store::invalidateTags` or use the
 `PurgeTagsListener` from the [FOSHttpCache][3] library to handle tag 
 invalidation requests.
 
+### Pruning expired cache entries
+
+By default, this store removes expired entries from the cache after every `500`
+cache **write** operations. Fetching data does not affect performance.
+You can change the automated pruning frequency with the `prune_threshold`
+configuration setting.
+
+You can also manually trigger pruning by calling the `prune()` method on the
+cache. With this, you could for example implement a cron job that loads the store
+and prunes it at a configured interval, to prevent slowing down random requests
+that were cache misses because they have to wait for the pruning to happen. If you
+have set up a cron job, you should disable auto pruning by setting the threshold
+to `0`.
+
 ### WARNING
 
 It is possible to configure other cache adapters or lock stores than the