bind config question

[Bio Hazard]

In my /var/log/messages file, every hour I see a line like this:

Sep 25 11:35:11 net named[9124]: Cleaned cache of 8 RRs

I assume that this is restarting the named (DNS) server.  I'm guessing
that within the past hour, named resolved 8 domain names, and once the
hour had passed, it flushed its cache.

If this is what's happening, is there a way to increase the time of
resolved domain names within the cache?  So it wouldn't have to do an
authoritative lookup of the same domain names every hour?