Yeast and Fermenting
"Beer yeast is a single-cell living organism. In its microbial world it is classified as a fungus. The activity during its life cycle offers tho the brewer the gift of beer. The "living" part of your beer should never be forgotten or taken for granted. Yeast is not simply some "thing" that is added as an ingredient and quickly forgotten. Sure left on its own accord it will indeed take it upon itself to make beer. But I can assure you that merely thinking about yeast as living organisms and involving your own common sense in understanding what they are doing will make your beer better."
-The New Complete Joy of Homebrewing- Charlie Papazian
Ok lets get down to the nitty-gritty of yeast. Like what was said before yeast is a living breathing organism, which if given a proper environment and food will do quite well. Ok let us start with the food part of that. Yeast, among a whole hell of a lot things in this world feed in some sort of sugar. In fact if you break it down yourself, that is something that we all need to maintain life as well. Though yeast uses sugar as its soul source of energy. With out sugar your yeast will either become dormant or die. Another main ingredient that yeast needs, though only for a limited amount of time is oxygen. For about the first 8-10 hour after you add the yeast to the wort it goes through this process where it tries to absorb all the oxygen that it can get. After it gains all the oxygen that it needs it will start to multiply at an alarming rate, where it will use up the oxygen that it has stored. Try to remember that yeast is microscopic and the little amount of oxygen that is in the top of a closed fermenter is all that it will need to gain oxygen. Also before you add the wort, when you add the water. By pouring the water into the fermenter you oxidize it to where it creates o2 molecules that the yeast will remove and use. From this point the yeast will now start the fermenting process, that will eventually create Alcohol. In the feeding and multiplying of the yeast there are to by- products created, CO2 and Alcohol. The CO2 you will see when your water lock starts bubbling, which the homebrewers that have already started brewing will be overly fascinated with this. So in turn the Oxygen environment that you origanlly started with will soon become one made up of mostly Carbon Dioxide, and for those science majors, the environment is either micro-aerophilic to anaerobic.
Now to desribe the perfect Environment. Yeast will grow just about anywhere though there are some environments that it prefers more then most.
pH: Yeast prefer a pH of around 4.5 That is why choosing water is so important. If you use water that is way over or way under 4.5 it can throw the yeast way off and cause them to ferment in ways that you do not want. Think about it, how would you feel if you lived in acid rain?
Temperature: This one of the major factors in homebrewing, because yeast react differently at different temperatures and make different by-products that will eventually flavor your beer. Yeast can grow in a wide temperature range, around 33-90 degrees F. Though yeast prefer a set temperature range, depending on the type of yeast. Ale yeast grow best in a temperature range of 60-75 degrees F (16-24 degrees C). Where is lagers grow best at a temperature range of 35-50 degrees F (2-10 degrees C), which is a bit lower than ales. Now that doesn't mean that if you brew a lager at 68 degrees that it will be ruined, For anybody that has had a "steam" beer, this is all that this is.
