Node.JS с RedisStore таймаут сессии

I'm using Redis to store sessions in my node.js app, hosted on heroku, but redis is keeping the session stored, how can i make them expire automatically?

My express app is configured this way:

var app = express.createServer(
  express.static(__dirname + '/public', { maxAge: 31557600000 }),
  express.cookieParser(),

    express.session({ secret: 'secret', store: new RedisStore({
          host: 'myredishost',
          port: 'port',
          pass: 'myredispass',
          db: 'dbname'
      })})
);