by Les Saidel - October, 2012
Yeast is a single cell organism (think of an amoeba) belonging to the family of fungi. The yeast family contains thousands of different species, each with a slightly different structure and behaviour but with the same basic functioning.
Yeast cells are microscopic and cannot be seen by the naked eye. They are ubiquitous, existing all around us - in the air we breathe, in the soil, on our skin and on peels of fruits and vegetables. Yeasts are sometimes beneficial to the human body and sometimes harmful. They proliferate in our digestive systems and aid metabolism by synthesizing B-complex vitamins and other vital nutrients. On the flip side, yeasts may cause infections on the human body (candidiasis).
Besides the "wild" yeast that occurs naturally all around us, certain specific strains of yeast are produced by the food industry and aid in the production of many different foodstuffs - bread, beer, wine, salami, amongst others. The specific species of yeast used in the food industry is called saccharomyces cerevisiae, otherwise known as brewer's yeast or baker's yeast, which are slight variations of each other, one optimized for its increased alcohol production (brewer's yeast) and the other for its carbon dioxide production (baker's yeast).
Yeast is produced commercially by growing the saccharomyces cerevisiae yeast culture in large vats containing sugar/mineral solution under controlled temperature conditions. The yeast that grows in the vats is skimmed off and then either granulated, pressed into cubes or freeze dried to make the different types of yeast we find in the supermarket. The dried yeast is usually mixed with a rehydrating agent, most commonly sorbitan monostearate that allows it to speedily dissolve in water.
99% of commercial bakeries use baker's yeast to produce their baked goods. The advantage of baker's yeast is that it has a high carbon dioxide production capability, allowing the bread to inflate to a greater degree and an accelerated fermentation rate, thus allowing more bread to be made in a shorter time. This short fermentation rate has another advantage - it does not produce a sour taste in the breads and is thus advantageous for sweet breads or baked goods.
Some bakeries use natural, or sourdough yeast to ferment their breads. These yeasts are not of the saccharomyces species, but other "wild" strains that are captured from the air. These natural yeasts are more appropriate for whole grain breads such as rye, whole wheat or spelt breads, where the additional "sourness" they add, due to longer fermentation, complements and improves the flavour of the bread.
Now to the subject of yeast allergies.
Firstly let us differentiate between a yeast infection and a yeast allergy. Yeast infection or candidiasis, caused by the the candida family of yeasts, occurs because of a chemical imbalance in the body which allows the candida yeast to proliferate. Yeast loves a warm, wet environment and this is usually the location of the yeast infection. Yeast infections usually require medication to treat them. To prevent them, the chemical balance needs to be corrected, sometimes by adding beneficial organisms to balance the candida organisms, such as acidophilus.
A yeast allergy is something different. It is an auto immune reaction to the yeast protein in the digestive system. Certain persons are allergic to the proteins present in the yeast cells. When these proteins are found in the digestive system (or on the skin), the immune system of the person with the allergy produces antibodies to attack the yeast proteins. These antibodies attach themselves to white blood cells and release a chemical called histamine. This produces the swelling and sensitivity symptoms of the allergy.
It does not matter whether the yeast are alive or dead (for example killed by heat during baking), since it is the protein content of the yeast that causes the allergic reaction, not the live organism itself.
Many times people mistake yeast allergies with an allergy for the rehydrating agent sorbitan monostearate, present in dried yeast. In these cases, simply switching to the "wet" form of yeast solves the problem.
In other cases the allergy is specific to a certain strain of yeast, such as saccharomyces. For these people, switching to bread baked with natural/sourdough yeast may solve the problem.
To verify that you do have an allergy to yeast, you should visit an immunologist who will render a series of tests by applying different allergens either by pin prick or by patch to your skin and observing the reaction to each. This is the only way to truly determine whether you do have a yeast allergy and to which strain. Please note that the symptoms of a yeast allergy are common to many other allergens such as gluten, sesame etc. and the only way you can be sure that the allergy is to yeast is by being tested.
For those who do have a yeast allergy, bread is not the only thing they need to be careful of. Other foods such as grapes, plums, malt drinks, MSG, wine, soy sauce, peanuts, corn and even chocolate may cause an allergic reaction.
Yeast allergies are usually genetic, so if you have one, your kids may too. It is worth getting them checked.
The good news is the majority of the population are not allergic to yeast, but if you suspect something, like repetitive symptoms after eating yeast containing foods, you should be tested.
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