Re: The FCC, eh?
Ethanol and also hops. Hops are naturally antibacterial. If your beer is at least 2% ABV and also at least 20 IBU (International Bittering Units, a measure of isomerised alpha acids derived from hops) your beer is unlikely to spoil.
A long time ago in a monastery far far away (or possibly just down the road depending where you live) monks brewed ale (not beer in those days) for the local community. They did mash the grain more than once as mentioned above, they kept the very strongest ale for themselves, the normal strength was for evening consumption by adults, and the last runnings made small beer for kids and mornings.
Some modern breweries still get two runnings from one batch of grain: this is called parti-gyle brewing. Fullers is a good example of a brewery who use this method. The first runnings (strongest) goes into one kettle to be boiled, the second runnings (weakest) goes into a second kettle. They then blend different proportions of strong & weak to get different strength beers as desired. If the two kettles are boiled with different varieties of hops then the resulting stronger and less strong beers can taste very different, even though they were made with the same grain.
p.s. Brewing is my day job.