When people ask, what is yeast? They seldom realize that it is actually something classified as a fungi, of which there are over 1,500 different species. Yeast, or eukaryotic micro-organisms to give it its correct meaning, is actually a living single cell. Yeast used as a leavening agent in bread making is often known by the name of baker’s yeast, it works by converting the fermentable sugars in the dough into carbon dioxide and ethanol. This yeast is of the Saccharomyces cerevisiae species and is also used in the fermenting of alcohol, where it is then known as brewer’s yeast.
Louis Pastuer was the first to be credited with discovering and understanding the methods of culturing pure strains of yeast in the 1850’s. His discoveries lead to the development of the process that is still used today.
There are two forms of yeast that can be bought today:
Fresh yeast is an ivory color and has a yellowish hue, and is more often used by professional bakers. This yeast is soft, moist and can easily be crumbled. It is, however, highly perishable and needs to be kept in a chilled environment and used within a short time of opening.
Dry yeast was developed for the United States armed forces during World War II. This yeast did not need to be kept in a chilled environment, had a much longer shelf life and was not affected by temperature changes anywhere near as much as fresh yeast.
Which Yeast to Use
When using fresh yeast you should always ensure that there no dark or dried areas on the yeast. As mentioned above fresh yeast does not have a very long shelf life and so can work out expensive to use unless you are doing a lot baking all in one go. Also I have found when using fresh yeast that it does not mix easily with sugar which results in the cells breaking down and the dough not rising properly.
Dry yeast comes in a packet and can be all shapes and sizes is never easy to decide which brand to buy. I’ve tried quite a few different types from regular active dry yeast to the rapid rise yeast and I have to say that I have found that I can use both fresh and dry in my bread maker, but I do prefer the regular dry yeast as I can use this either by hand or in my machine.
Rapid Rise yeast does work in half the time but I have found that there was a lose of flavor and the texture of the dough lacked elasticity.
Some recipes ask for yeast to be added to warm water first, this allows the yeast to activate, which in turn helps bubbles form and this enables the dough to rise. All action within the dough will stop once the mixture is placed in the oven as extreme temperature kills off yeast.
I have also discovered that sweet dough need more yeast, which sometimes can be double the amount normally used in bread dough. This is because the extra sugar used to sweetened the dough tends to slow the yeast down .Although yeast is more commonly known as being used in alcoholic drinks and baking, it can also be used in making batter for fish too.
I should add that when ever cooking with yeast ensure that you use the correct quantity as too much will give the dough an over powering yeasty taste and too little will cause the dough not to rise.