A question that comes up a lot on various homebrewing forums (or is that fora?) is what to do with the spent grains from brewing. First, for those who don't brew themselves, I should explain what I mean by "spent grains". Beer's backbone, its main ingredient, is malted barley. You can use other kinds of malted grain (like wheat), but barley is the principle grain in most beer. Malting is the process of just barely sprouting the grains, then drying and lightly kilning them to halt the sprouting process. As a kernel of grain sprouts, its chemical composition changes. Most important for us, if you take sprouted (malted) grain, grind it up, and add hot water to form a porridge at just the right temperature (typically you end up with something in the 150 deg F range) the enzymes in the malted grain will be activated and they will begin to crack down the starch in the grain and convert it to malt sugar (mostly maltose). Further on in the process this sugar, in turn, is converted by yeast into alcohol and carbon dioxide.
What's left over after the enzymes have done their thing and the sugar has been washed away into what will become your beer is called "spent grain". But it's only spent from the standpoint of being able to get more sugar out of it. The grain still retains almost all of its protein and, of course, its fiber content. That means it's dynamite animal feed. And so here at the Palm HQ it's easy to know what to do with spent grains -- we feed our animals. Both cows and horses absolutely love the spent brewing grains. I just let the spent mash from a batch cool down and then feed it out over the course of three or four days.
Homebrewers who don't keep farm animals will sometimes add the spent grains to their compost pile, make dog biscuits, or sometimes even cookies or other baked goods for human consumption. I haven't tried any of those other things, so Ican't really comment.
Commercial breweries routinely sell their spent mash to farmers as animal feed. They do the same with spent hops and the enormous quantity of yeast that is left over after their large-scale fermentation. I have usually just dumped my leftover yeast onto the lawn. One time I thought it would be a healthy fertilizer, so I dumped some at the base of a maple sapling I had started that year. Over the course of the next few weeks all the leaves fell off and the poor thing almost died. It's doing okay now, but I've gone back to just dumping them out. But yeast is highly nutritious and commercial breweries sell the yeast. They also sell the carbon dioxide that is generated during fermentation. So you see, nothing much goes to waste in the brewing process.
Some homebrewers are concerned about their water useage. Brewing requires a fair amount of water, not only to mash and rinse the grains but also to chill the boiling wort before you add the yeast. Again, here on our farm I don't really waste anything. I use the very hot water that first comes out of the wort chiller to clean my equipment. Then, when it starts to cool off, I capture it in 5 gallon buckets and use it to fill the water troughs for the animals.
Overall, then, brewing is a fabulously efficient process -- nothing is "wasted" except, I guess, the fuel needed to heat the water and boil the wort. But then again, it's awfully hard to claim that anything is truly wasted when it results in something as wonderful as beer.