With more than 1,500 species, yeast can be found almost everywhere. A single celled microorganism yeast is not made but grown. In essence, this is what you are doing when you create a sourdough starter, collecting wild yeast and growing it.
To grow, yeast needs food (sugar), the right temperature and oxygen. Whether making beer or bread, the process starts out the same. The enzymes in yeast convert sugar into alcohol and carbon dioxide. A baker wants to capture the carbon dioxide to leaven the bread and make it rise. A brewer wants to capture the alcohol.
Too hot to handle!
As a living organism you can easily kill yeast, and hot temperatures are a great way to do this. Anything over 59°C will kill your yeast. While cold temperatures won’t kill the yeast, it also won’t encourage it to grow, which is why yeast is stored in the fridge. The ideal temperature to get that bug multiplying is between 24°C–35°C.
Though man has harnessed and used yeast for over 5,000 years, it was Louis Pasteur’s invention of the microscope that led to our understanding of yeast and thus the ability to control and manufacture it. This was great news for commercial bakers, and the likes of me who, while I appreciate a delicious sourdough loaf, has no patience for growing and maintaining my own starter. Instead, I rely on bought yeast which comes in several different forms.
Also known as cake or compressed yeast, fresh yeast is preferred by many professional bakers. Although it is harder to get and has a much shorter shelf life than other or dried forms of yeast.
Fresh yeast contains around 70% moisture and does not require you to activate it like dried yeasts.
Active dry yeast
These granules of yeast have had the moisture removed, giving a shelf stable yeast with a longer shelf life. For best results the yeast granules need to be activated (sometimes called bloomed) in warm liquid before being added to the dry ingredients.
Instant yeast is more finely ground yeast that can be added directly to the dry ingredients in a recipe without being activated. It also tends to rise faster than active dry yeast.
Surebake yeast or breadmaker yeast
Especially formulated for beadmakers with a mix of active dry yeast and bread improvers such as wheat flour and sugar.
Created to be a food a product not a raising agent, the yeast cells are killed during manufacture. Used to add a cheesy, savoury flavour to food and a handy ingredient for vegans.