Beer is a cultured food product, like yogurt or pickles. It is made by creating a liquid that is ideal for the growth of microorganisms - lots of available sugar for example - and then inoculating that liquid with microorganisms and letting them go to work. I say inoculate but one traditional way of doing that is putting the liquid in large flat (high surface area) containers in an attic and leaving the windows open. It is safe to drink for two reasons: 1) the pre-fermentation environment is better suited to benign microorganisms than to harmful ones, so the odds of a dangerous culture developing are low, and 2) microorganisms tend to change their environments to interfere with the growth of other microorganisms, so the growth of yeast makes the environment (the wort/unfinished beer) difficult for bacteria to live in etc.
Beer isn't even boiled, necessarily. The wort is raised to temperatures which activate enzymes in grain, converting starch to sugar which is then leached out. Boiling is not really desirable as it is above the enzyme activation temperatures. Brewers centuries ago learned to watch how the water behaved and try to hold it at a pre-boil because they couldn't directly measure the temperature.
Last edited by Him; 12-06-2012 at 04:36 AM.