After last week's post about Yeast, I received a couple of questions asking for a bit of clarification. I thought it would be a good idea to post the questions and my response here.

Question 1

In the article you wrote:

'which is the classic bakers or brewers yeast'

With that statement, it took it to mean that they are one and the same yeast but having read further it would seem not to be the case. Have I read it properly?

Answer

Sorry if I made it a bit confusing. The traditional general purpose brewers yeast is indeed the same as bakers yeast. The other 2 yeasts I mention are a bit more specialist.

Question 2

Thanks Mike. I wonder how they isolate specific yeasts, as in the pombe one?

Answer

One way is to put a dilute solution of growing culture on an agar plate, which is a kind of jelly made using the growth medium, and leave the yeast to grow for a few days. After that you pick out individual colonies, which will usually have grown from single yeast cells. There is likely to be 100s of colonies of various types depending on what is present.

You can then do whatever tests are required to identify them, which these days will often involve some kind of genetic test. If you are wanting to brew wine or beer you can make trial runs with the different colonies to see how they affect the flavour. This is probably how they ended up with the different wine yeasts where you can buy yeast 'optimized' for different types of red or white wine.