Exploring the properties, strains and functions of the fungus that makes your bread and baked goods grow.
Yeast belongs to the group of living things called fungi and has been used in the production of bread, wine and beer for thousands of years. The scientific name of the yeast used in food is Saccharomyces cerevisiae, which includes all the varieties of baker’s yeast.
Bakers often purchase yeast that is active dried, fast-acting dried, bulk, or compressed. Each type is essentially manufactured the same way, and they all belong to the same species. The only difference is that the final steps of the manufacturing process are slightly different. Different types of yeast may need to be measured and used differenlty. In addition, different strains of yeast can exist and are commercially available. Certain strains will function particularly well in specific products, such as frozen dough, baked goods with low amounts of fermentable carbohydrates and items high in fibre.
The basic and most important action of yeast is the production of carbon dioxide (CO2) gas, which helps the dough rise and contributes to the formation of its structure. The production of CO2 is based on the ability of the yeast to ferment the sugars that are added to the dough, as well as the natural sugars found in the flour. The sugar (sucrose) we normally add to the flour to produce yeast-raised baked goods is composed of two simple sugar molecules: glucose and fructose. The yeast is not capable of absorbing the sucrose into its cell in order to ferment it. Because of this, it secretes an enzyme invertase into the dough, which almost instantly hydrolyzes or inverts the sucrose into the glucose and fructose components. The yeast ferments glucose and fructose at the same rate when they are present separately. However, when present as mixture, such as when the sucrose is inverted, the glucose is preferentially fermented first and when it is exhausted, the fructose fermentation follows. Yeast will also ferment other sugars as well at different rates.
During the fermentation process (which normally occurs under the anaerobic conditions of the dough), most of the yeast’s activities are directed towards the production of the alcohol and gas, with very little, if any, growth and multiplication.
When yeast is exposed to plenty of oxygen and the proper environment and food, growth and multiplication becomes the most predominant activity.
In order to begin its activity, yeast requires the proper moisture level. The temperature of the dough is also very important. A range from 27 C to 35 C is normally necessary. The yeast also requires the proper pH, or acidity level. It can function in a wide range of pH, from 2.4 to 7.4. In order to optimize its activity, it is good practice to maintain the pH of the dough in the range of 4.0 to 6.0. It is also necessary to have available a good supply of food for the yeast, such as fermentable carbohydrates (sugars), in order to achieve proper fermentation and production of the proper amounts of carbon dioxide. Salt also plays a very important role. A certain amount of salt is required to control the fermentation and the growth of yeast. A salt content of over 1.5 per cent inhibits yeast activity due to its chemical action, as well as due to changes in the osmotic pressure in the surrounding environment.
Fermentation changes the environment of the dough. Accumulated waste products, such as alcohol, carbon dioxide and various organic acids, contribute to the changes. The alcohol completely evaporates during the process of mixing, proofing and baking, but in combination with the organic acids, it gives the characteristic aroma of freshly baked goods. The organic acids, and other compounds such as esters that are produced, add flavour. Yeast also alters the pH of the dough and softens or mellows the gluten.
Recently, there have been R&D achievements in yeast that assist certain nutritional and health-related challenges.
As is the case with other fungi, yeast contains ergosterol, a precursor of vitamin D. When fungi such as mushrooms and yeast are exposed to controlled UV light, the ergosterol is naturally converted to ergocalciferol, which is vitamin D2. Using such yeast in formulations provides the opportunity to enhance the content of vitamin D in yeast-leavened baked goods.
In another recent development, the yeast can be modified to reduce acrylamide in baked goods. Acrylamide is an undesirable chemical substance produced from the reaction of protein and carbohydrates when food is exposed to heat (in particular, the reaction between amino acid asparagine and reducing sugars).
Many strains of yeast are currently available to the food industry and I am sure many more will be discovered or developed in the future.
For more information, or fee-for-service help with food technical and processing issues and needs, please contact Dr. John Michaelides at John Michaelides & Associates at 519-743-8956, or at Bioenterprise at 519-821-2960, ext. 226, or by e-mail at
. Bioenterprise is a company of experienced professionals that coach and mentor emerging agri-technology companies from planning to startup to profitability and beyond.
Technical Talk: March 2013
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