By request of my lovely girlfriend Kelly, we are going to discuss yeast, not yeast infections... haha gross
All you home-brewers out there are used to the following series of events:
1) Decide to brew beer
2) Drink beer and fantasize about beer you are about to make
3) Go to homebrew supply store to buy ingredients for brew
Now it gets important!
4) Select one of the many many yeast strains available for your future brewy goodness
5) blah blah blah
6) Yummy beer!
Buying individual yeast strains for every beer is not a reality at the larger scale. At many of the breweries that I am familiar with (including ours) there are only a handful of yeast strains servicing many beers. Actually we use one yeast strain to make eight of our beers! WOW!!! AMAZING!!! Also, once we get a yeast starter, we will use it over and over and over again (more than 10 generations at a minimum) HOW IS THAT POSSIBLE???
Carefully is the answer. We buy a yeast starter from a lab, add it to a brew, and then harvest it for another brew. To ensure no contamination of the yeast the harvesting, handling, and transferring of our yeast is done in dedicated kegs that are meticulously cleaned after every use. We take care to harvest the yeast at the proper time during fermentation and if it sits in the cooler too long before it can be used again, it is acid washed and fed. We also have to ensure that the yeast we harvest will be suitable to make the subsequent beer (for example, don't harvest from a stout to make a pale ale).
From what I can gather, different breweries have very different yeast handling practices. Some buy starters more often than others. Some use their yeast for many many generations, some not so much. Some have many different styles of yeast and some have only one or two.
I'm exhausted, I'm going to bed. We have a puppy for only two more days, and he must know it because he is becoming more and more annoying by the day! Until adoption day (thursday) I will be up at 5:30 am... again.
Cheers, Prosit, and Skoal!