Beauty and the Yeast

Enthusiasm is the yeast that raises the dough.
- Paul J. Meyer

How and Why is Yeast Used in Food

I remember my mother baking bread.  She always started with a small bowl of warm water and sugar, over which a little package of yeast was sprinkled.  I was told that it would come alive in the water.  As a little kid, I was fascinated.

Active Dry Yeast

Active Dry Yeast

Last weekend, as I was baking bread, I began to wonder about the yeast.  So, okay I knew that it was a living organism and that it produced gases that would eventually rise the dough.  I also knew that it was somehow used to create the alcohol in beer.  But, I wanted to know the details.  What is it exactly?  Where does it come from?  How is it made?  Is it good for you?  Etc…

After some research, this is what I’ve found out. It is sort of a plant composed of only one cell. Actually, it is in the same family as mushrooms and other fungi. It been used for thousands of years, dating back to ancient Egypt.  In fact, it was one of the first cultivated/domesticated organisms.  It can be found everywhere, and is common on plants leaves and flowers, in the soil, and in salt water. One species, Saccharomyces cerevisiae, started to be sold commercially by the Dutch around 1780. It is still sold today and is used in baking and fermenting alcoholic beverages.  However, baking and brewing varieties are generally different strains, cultivated for specific requirements.

Activating Yeast

Yeast Sprinkled on Water

Brewing

Alcoholic beverages are created when carbohydrate containing plant materials are converted by the yeast into ethanol (C2H5OH).

Baking:

Similarly, when baking, it feeds on the sugars found in the dough. Initially, the yeast respires aerobically, producing carbon dioxide (CO2) and water.  When the oxygen is depleted, fermentation begins, producing ethanol as a waste product; however, this evaporates during baking. The CO2 gas is trapped in the dough and causes it to rise.  As the dough is baked, the yeast dies, leaving a soft spongy texture.

These days there are basically two types of yeast you can buy for baking:  Active Dry Yeast, and Instant.  The instant variety might also be called Bread Machine or Rapid Rise Yeast.  You can also buy Fresh Active Yeast, sold in cake form, but I don’t see it often.

The main difference between the two types is that instant can be added directly to dry ingredients and does not need to be “proofed”.  Recipes using active dry yeast generally need two risings.

It needs to be stored in a cool, dry place.

It is often sold in 1/4 oz. packets.  If you’ve buy it in bulk, then when the recipe calls for a 1/4 oz. packet, use 2 1/2 tsp.

Generally you can substitute the different types in your recipes but there are limitations.  If you’re using a bread machine, it is probably better to stick with instant yeast.  See the bread world link below for more information.

How is it Produced?

In simple terms, yeast is farmed like almost any other food.

During commercial production, molasses is used as a food source.  Before feeding the molasses to the yeast, it needs to be sterilized and clarified.  This prevents bacteria from being introduced to the manufacturing process.

Once the molasses has been prepared, it is fed to seed yeast.  Seed yeast are maintained in a laboratory so that wild yeast does not contaminate the final product.   The seed yeast is placed in small flasks and allowed to grow.  As it grows, it is transferred to larger and larger tanks.  Eventually it could end up in 1000 gallon tanks.

Now, it is called stock yeast.  It is separated from the alcohol that is naturally produced as part the fermentation process, and moved to 40000 gallon tanks until it is ready to be harvested.

Harvesting is accomplished by separating it from the liquid.  This is done by spinning the yeast in large centrifugal pumps.  The result is a whitish liquid call cream of yeast.

The final stage is the drying.  How it is dried depends of the desired end product.  Cake yeast is dried the least, and it characterized by its high moisture content.  Active dry yeast is basically just cake yeast that has been processed one step further.

Is It Good For You?

De-activated yeast is often included in vitamin supplements because it is high in protein, and a rich source of B vitamins such as niacin, folic acid, riboflavin, and biotin.   Some pro-biotic supplements also include it.

However, some people can develop allergies and so need to avoid foods like bread and beer.

Yeast is Ready

Yeast Ready to be Added to Bread Dough

Sources:

http://en.wikipedia.org/wiki/Yeast

http://www.yeastgenome.org/VL-what_are_yeast.html

http://www.breadworld.com/Science.aspx

Red Star Yeast

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