will redis delete my old express.js sessions?

i'm using redis as my session store for a node.js + express app...will it automatically delete old sessions after they expire?

...or do I need to do some cleanup on the server side? (so the db doesn't grow too large)

  var RedisStore = require('connect-redis')(express)

  app.use(express.session({
    store: new RedisStore({
      host: cfg.redis.host,
      db: cfg.redis.db
    }), 
    secret: 'foobar'
  }));