I have just installed mod_pagespeed on the server and have set the extend_cache option to enabled. In the instructions it says that I should set the http headers cache-control to expire in about 1 year.

I am not sure how to alter that setting, other than by adding a header tag in individual html pages and would like to know if there is a shortcut option to set the cache-control expiration date across websites on the server.

Currently when I view my webpages, the headers (using firefox live http headers addon) are showing
Cache-Control: max-age=0, no-cache, no-store

I thought maybe something in httpd.conf, and having googled to find an answer but I am not finding any information on how to do this. Does anyone have any information on altering the cache-control for websites on a server?