time based expiration for fragment caching

Does anybody have any suggestions on how to do this? I have tried all kinds of plugins , googled all over the place but can't get it to work for 2-3 days now:

I use simple fragement caching like this: <% cache do %> <%= render :partial => @groups %> <% end %>

and in the controller somthing like this:   def index    unless read_fragment 'index'     fetch_groups nil     end   end

THIS DOES WORK. I am able to expire this cache from the controller. I have not changed any of the default caching settings.

Now I am looking for a solution to achieve automatic time based expiration of such a fragment cache.(I didn't get plugins like cache_foo, timed_fragment_cached to work.) I think it might have to do with memcached issue. As a lrealtive newbie I am confused whether memcached is a.) needed for this b.) already installed by default or not.

Can anybody point me to a relatively easy way on how to do this?

Thanks so much! Justus

Ok, let me rephrase this:

Is there a simple way to do time based expiration for cached fragements WITHOUT using memcached?

Thanks, Justus