Yeast

Yeast is a wonderful organism.  In my previous career as a microbiologist I messed around with Salmonella, Campylobacter, E. coli, Rhizobium but as wonderful as all these microbes are the yeast that give us bread and beer, wine and whiskey must be some of the most wonderful. 

Different types of yeast will contribute different characteristics to the food they're used in.  They can affect the flavour, colour and texture of food and for many food producers making sure they are using the right yeast is vital. Packets of dried yeast used in baking are a particular type or strain.  They are carefully selected, grown and dried to make sure every packet is the same and the breads, beer, wines and spirits they are used to produce are always the same.  When you make sourdoughs they use the yeast and other bacteria found in the air to make something unique and specifc.  No sourdough starter is the same and they change slowly over time.  This can be both good and bad, no bread will ever be exactly the same but have its own unique characteristics that repesent the microbes in our own environments.  This is why I want my own sourdough starter that contains the microbes from my home, rather than buying a commercially produced starter (or even using someone elses).  Sourdoughs are highly personal, perhaps in ways you don't want to think too much about! Similarly, wine grapes are covered in natural yeasts and other organisms that contribute to the special characteristics of a vineyard.

Yeast is a living organism.  It makes bread rise by feeding on the sugars and starches in the flour.  Like Humans this produces carbon dioxide, bubbles that are captured by the bread dough (which is why you need to do all that kneeding) and make the bread rise.  As the bread is baked the carbon dioxide expands with the heat and causes the (hopefully) dramatic 'oven spring' as the bread expands in the oven.  Another product of yeast growth is alcohol.  Different yeasts are therefore better for bread making and brewing.  The different flavours yeast confers to foods depends on how each strain breaks down the different consituents of the flour (in the case of bread) or grapes (in the case of wine) it is growing on.    I would love to better characterise my sourdough starter and find out what yeast and other organisms make my bread rise and taste so good.

Yeast are so important to our food and economy that they have their own culture collection and website to make sure that those yeasts that contribute to the viability and taste of some of our favourite foods and drinks are stored properly. Love it or hate it Marmite wouldn't be Marmite made from a different type of yeast.