Heroku NODE_ENV environment variable

I'm running a Node project with Heroku as my main deploy target. In dev environment I'm using grunt to start the web server, however in production I prefer to launch the app directly with `node app` Here's my Procfile: ``` web: bin/web ``` And bin/web: ``` #!/bin/sh echo "NODE_ENV=" $NODE_ENV if [ "$NODE_ENV" == "production" ]; then echo "Starting the server with node app" node app else echo "Starting the server using grunt" grunt fi ``` The first `echo` is for debugging. heroku log is showing: ``` app[web.1]: NODE_ENV= ``` Basically, meaning NODE_ENV is not set. (and the app starts with grunt instead of `node app`) The docs say that "The NODE_ENV environment variable defaults to production, but you can override it if you wish" What am I missing?