Elixir not autoprefixing when using --production flag

I'm hoping someone can shed some light on this issue.

I've searched around for how to make elixir autoprefix my SCSS files. At the moment it is compiling and minifying them, but when I check them out in browser and do a search for any prefix (e.g. -moz, -webkit, etc.) it returns 0 results. It doesn't seem to be autoprefixing it at all? What's more is that every attempt to search for a solution to this problem leads me to threads where people are saying that it's done automatically, which doesn't seem to be the case for me at all.

I've tried adding code such as this to my gulpfile.js: elixir.config.css.autoprefix.options.browsers = ['> 1%', 'Last 2 versions', 'IE 9']; But no such luck...

Am I missing something really obvious?

Thanks to anyone who can shed some light on this.