Yeast - Types of Yeast

What is yeast

What does "yeast" mean?

In biology, yeasts are monocellular organisms belonging to the kingdom of fungi. In the kitchen, on the other hand, the term yeast has a broader meaning and is extended to any micro-organism, or chemical substance, capable of "swelling" a mixture by incorporation of gaseous bubbles.

Types of yeast

There are two main types of yeast:

• Natural yeasts or proper yeasts: brewer's yeast, sourdough or sourdough, kefir
• Chemical yeasts : tartaric acid, cream of tartar, bicarbonate of ammonium or sodium etc.

The adjective "chemical" does not necessarily have a negative connotation: each type of yeast has its own advantages and disadvantages, which make it suitable for particular uses rather than others. It goes without saying that chemical yeast is not the protagonist of a real leavening, given that it does not produce any microbial fermentation.

"Physical" leavening

Alongside natural and chemical leavening, there is also a so-called physical leavening.

For example, in the preparation of the puff pastry, in baking there is a leavening because the water of the dough evaporates and is trapped in the impermeable layers of fat, which prevent the sheets of pasta from sticking together.

In meringues and other preparations based on whipped egg whites, the mechanical action of shaking incorporates minute air bubbles, which significantly increase the initial volume, up to 6/8 times.

Natural Yeasts

Beer Yeast

How does brewer's yeast work?

The so-called brewer's yeast is nothing but a culture of Saccharomyces cerevisiae, the most important microorganism in the culinary field; occasionally Saccharomyces exiguus (also known as Saccharomyces minor ) is also used, a fungus common in the environment and above all on the surface of fruits, cereals and vegetables.

Curiosity

Saccharomyces cerevisiae, in addition to being the most widely used yeast in the kitchen, is studied and applied as a bioremediation in purifying arsenic and other industrial residues, on which it seems to exert a lytic effect, of inactivation or bioabsorption.

In addition to leavening, Saccharomyces cerevisiae is involved in the production of beer and wine; at the industrial level, it is used for the synthesis of ethyl alcohol. By prematurely interrupting the fermentation of the must, a non-alcoholic fermented beverage can be obtained (eg root beer, kvass, mauby).

This yeast draws its nourishment from glucose and other sugars (such as galactose and fructose), which metabolizes producing waste substances which are very useful for us. If the fungus works in the presence of oxygen, it mainly produces carbon dioxide (fundamental for leavening); if instead it works in the absence of oxygen it mainly produces ethyl alcohol (alcoholic fermentation).

What is important for leavening is above all the production of carbon dioxide; this gas, in fact, once released, increases in volume due to the high temperature and is trapped in the dough making it increase in volume and making it soft; fundamental in this sense - in addition to the partially solubilized starch matrix thanks to the mixing procedures - is the presence of gluten, a sort of elastic protein net that develops following the processing of the mixture with water.

Notes : not all flours form gluten and this is why some do NOT lend themselves to baking.

On the market, brewer's yeast is found in fresh loaves or powders (or granules) obtained by freeze-drying.

Benefits of brewer's yeast

• Cheap
• Natural
• Brings vitamins and minerals to the preparation
• Less leavening time compared to the use of sourdough.

Disadvantages of brewer's yeast

• Can cause problems with intestinal bloating. These effects are amplified by incomplete leavening and / or insufficient cooking of the product. However, much depends on the degree of individual tolerance and on the doses of consumption.
• Compared to the product obtained with sourdough, the one that uses brewer's yeast is less digestible and contains more tyramine.

What do you need to know before using brewer's yeast?

• The activity of brewer's yeast ( Saccharomyces cerevisiae ) is maximum around 26/28 ° C. For most of the recipes, leavening should therefore take place in an environment with a temperature of around 30/40 ° C (so that the ideal temperature is reached at the center of the dough); keep in mind that the yeast dies at temperatures of around 55-60 ° C, therefore - for example - the heat of a radiator turned on in direct contact with the dough is excessive.
• The activity of brewer's yeast is influenced by environmental humidity, which must be neither excessive nor incomplete (ideal around 70/80%). In this regard, professional bakers use chambers at constant temperature and humidity, to always obtain the best possible result. It is also important to avoid exposing the dough to air currents during leavening.
• Brewer's yeast is found on the market as fresh yeast pressed into cubes or as dry powdered yeast. There are no huge differences in terms of activity, as yeast in unfavorable conditions (deprived of water) does NOT actually die; rather, it enters a state of "apparent death", ready to "be reborn" as soon as the environmental conditions are favorable. The main differences between the two types of yeast are:
• Dry brewer's yeast can be kept longer, for about a year if kept in a cool and dry environment
• fresh brewer's yeast, on the other hand, can be kept for about a month, as long as it is kept in the fridge, at a temperature of 2 to 8 ° C
• in general, keep in mind that a yeast close to the expiration date or already expired is less active and tends to modify the organoleptic characteristics of the dough in an unfavorable sense.
• As a rule, it is advisable to dissolve the yeast in just warm water (40-45 ° C), sometimes with a little dissolved sugar (or malt extract); this is intended to facilitate the activation of microorganisms. If the water is cold, glutathione is lost from the yeast cell wall, making the dough more sticky and difficult to handle. Furthermore, with cold the yeasts slow down their activity.
• Also the type of water used for the dough is important, since it influences the final result. For example, a very alkaline water slows down the leavening time.
• Fresh brewer's yeast stored in the refrigerator should be brought to room temperature before use.
• The addition of a small amount of sugar (sucrose) or maltose to the dough promotes and accelerates the leavening action of the brewer's yeast.
• Putting yeast directly in contact with high concentrations of salt or sugar determines the death of the same due to the high osmotic pressure (it deprives the yeast of cellular water which is fundamental for its metabolism). Even an excess of butter and fats generally compromises the activity of the yeasts.

See also:

Homemade Bread Pasta

Video Recipes based on brewer's yeast

Video Recipes based on dried yeast

Doses and quantities of brewer's yeast

The doses of use of fresh and dried brewer's yeast are different; the dry one, in particular, has a slightly lower fermentation activity (with the same rehydrated weight), but contains many more cells per gram of product.

Yeast equivalence : 1g of fresh brewer's yeast = 0.33g of dried yeast = 4g of dried sourdough.

Sourdough or Mother Yeast

How does sourdough or sourdough work?

Sourdough yeast - also known as sourdough, natural yeast, sour yeast, growing pasta or sourdough - is obtained by taking a piece of dough (containing yeast) from the previous uncooked preparation. This compound must be stored and left to mature for a certain period of time. This sample - called head yeast - will act as a culture medium and reserve of yeasts, and will then be added to the next dough (of which a part will be taken for subsequent processing and so on).

It sounds simple, but it is a real art, which requires a lot of experience.

Benefits of sourdough or sourdough

• Unlike brewer's yeast, in sourdough yeast we find various types of microorganisms, such as saccharomycetes, lactic and acetic ferments that are "absorbed" directly from the environment. Precisely for this reason, in addition to carbon dioxide and alcohol, fermentative activity determines the production of acids and aromatic substances (for example lactic, acetic, propionic, butyric acid, etc.), to the advantage of the organoleptic characteristics.
• The higher leavening times required give lytic enzymes present in yeasts - such as proteases, lipases and amylases - more time to break down protein, lipid and starchy macromolecules into simpler nutrients. A product obtained with mother yeast is therefore generally more digestible. Among these enzymes there is also phytase, present in the outer shell of the grain, which - during the long leavening times - neutralizes phytic acid (an anti-nutrient, present in bran, which tends to prevent absorption by the intestine of some important minerals, including calcium, iron, magnesium and zinc); for this reason, a wholemeal bread obtained with mother yeast is also more nutritious and digestible. The acid paste can also have a probiotic action and eliminate (or reduce) the problems of abdominal swelling related to the consumption of leavened dough.
• The greater degree of acidity linked to polymicrobial fermentation, also guarantees a greater preservation of the product.

Disadvantages of sourdough or sourdough

• Rising with sourdough is a slow and difficult to standardize process. Therefore, this real art is now bound to very few traditionalists and to homemade bread.
• Many advantages (and disadvantages) are related to the microflora that makes up the sourdough, to its state of preservation and refreshment, etc. For example, the dough may be too acid or have an irregular pitting.

What do you need to know before using sourdough or sourdough?

• To use sourdough yeast you need to be very familiar with so-called refreshment operations. These are made by adding new flour and water to the sour dough, in order to give it the right degree of "strength" and acidity.
• On the market there is the dried mother yeast, which guarantees the relative standardization of the preparations, while maintaining many typical advantages of the use of this type of yeast. Generally, it is used in combination with a starter (small amounts of yeast or yogurt).
• If you want to prepare sourdough by yourself, plan for several failures until you have accumulated enough experience.

Preparation of sourdough or sourdough: Example

Phase 1 : to obtain a new sourdough it is first of all necessary to produce a mixture of water and flour, left in contact with the air so as to enrich the yeasts present in the environment.

• 2 parts of flour (eg 200 g)
• 1 part warm water (eg 100 ml)
• a teaspoon of sugar (or malt or honey) which acts as a starter.

Mix the ingredients and knead until the mixture is soft. Make a cross cut and let it rest in a glass container covered with a clean and damp cloth, at room temperature for 48 hours (during which it will double in volume).

Phase 2 (3rd-4th day): after 48 hours of rest, take a part of the mixture (eg 200 grams) and add it:

• 1 part of flour (eg 200 g)
• half of lukewarm water (eg 100 ml).

Mix the ingredients and knead until the mixture is soft. Then let it sit for 48 hours in the same way as for phase 1.

Step 3 (5th-6th day): after 48 hours of rest, repeat step 2.

Step 4 (7th -13th day): after 48 hours of rest, repeat step 3 but leave to rest for only 24 hours. Repeat every 24 hours for another 7 days.

Phase 5 (14th day): after two weeks from the beginning of phase 1, the sourdough will be ready. If the preparation is too acidic, extend phase 4 for a few more days.

Once obtained, the sourdough is stored in the refrigerator and kept alive and reproduced by means of subsequent refreshments every 2/6 days.

Refreshing operation of sourdough or sourdough: Example

The evening before preparation, take the sourdough from the fridge. Let it rest at least 15 minutes at room temperature and add flour and warm water in the proportions of:

• a part of sourdough
• one part of flour
• half a part of water
• if necessary add as a starter even a low teaspoon of sugar for every 150g of sourdough.

Knead and let it rest at room temperature for at least one night. The next day:

• take a part to be kept in the refrigerator for future preparation
• add the refreshed sour dough to the various ingredients of the preparation and proceed according to the recipe.

See also:

How to make sourdough at home

Homemade yeast bread

Video Recipes based on dried yeast

Other Types of Natural Yeast

Other types of natural yeast are:

• Biga
• poolish
• lievitino
• Rest dough.

Big leaven

The biga is a "raw" dough, little hydrated and composed of flour, water and yeast in very small quantities, to be used the next day to replace the yeast.

Poolish yeast

Poolish is a bakery ingredient also called "liquid biga". It is a semiliquid yeast obtained by mixing water with flour in equal parts and yeast in a very small quantity (proportional to the leavening times). It is prepared several hours before the final dough and left at room temperature for longer the lower the yeast content. When the poolish is ripe, the amount of flour needed to find the right consistency of the dough and the other ingredients is added. A second leavening phase follows before baking.

Watch the video: Homemade Poolish

Yeast leaven

It includes the addition of yeast in a little water, sweetened with sugar, honey, malt etc. It is used after half an hour of rest in a warm place; when it is ready a light foam will form on the surface.

Yeast paste from RipoRto

Take a portion of the leavened dough from the previous day, keep it for a day or two (not beyond) and use it in the following baking together with a small amount of brewer's yeast.

Chemical Yeasts

Ammonium bicarbonate

How does ammonium bicarbonate work?

With the ammonium bicarbonate we inaugurate the list of so-called chemical yeasts; it is precisely substances capable of triggering a chemical reaction from which gas is released, usually carbon dioxide. They are used above all for the leavening of sweets during cooking, given that the gas typically develops with the heating of the chemical yeast and / or through the interaction of more chemical leavening agents.

Humidity and pH also tend to play a very important role. Precisely because they do not need a resting time for leavening before baking, chemical yeasts are also called instant yeasts. For example, with heat the ammonium bicarbonate decomposes into three gases: water vapor, carbon dioxide and ammonia. It is mainly used in the confectionery industry for the production of dry biscuits, while at home it is rarely used.

Butter Nuts Biscuits

X Problems with video playback? Reload from YouTube Go to Video Page Go to Video Recipes Section Watch the video on youtube

Advantages of ammonium bicarbonate

Like all chemical yeasts, it makes leavening faster and safer Chemical yeasts are better tolerated by those suffering from intolerance or yeast allergy.

Disadvantages of ammonium bicarbonate

Ammonia is a gas with an acrid smell and when it does not completely evaporate (in the event of an overdose of leavening or incomplete cooking) it can impart a bitter taste to the product.

Freshly baked, baked products prepared with ammonium bicarbonate can have a slightly bitter aftertaste, which tend to fade as the product cools down. Ideal for desserts, it is not recommended for bread making; in fact it tends to give less digestible, less conservable and "artificial" flavor products.

What do you need to know before using ammonium bicarbonate?

When cooked, turn on the hood and open the oven keeping the face away from the vapors; the breathing of ammonia gases, in fact, as well as not very healthy, can cause episodes of lipotimia.

Chemical leavening powders must not be dissolved in a liquid, but mixed directly with dry ingredients (flour, sugar, etc.). Once the ingredients are mixed, it is good to bake the dough immediately.

In general, chemical yeasts fear atmospheric humidity very much, so they must be carefully stored in an airtight container.

When a recipe calls for the use of a certain type of chemical yeast, follow the instructions regarding the quantity and type of yeast suggested.

Video recipes based on ammonium bicarbonate

Cremor tartar

How does cream of tartar work?

Cremor tartar is the invented name given to potassium bitartrate. Once again it is a chemical yeast, mainly used to stabilize the whipped egg whites (thanks to its slight acidity it favors the coagulation of egg white globulins).

Other chemical yeasts

Often chemical yeasts are used in combination with each other and added with flavor corrections (such as vanillin); all this in order to reduce the negative effects of an overdose or prevent the yeast from freeing all the gas while the dough is still being processed.

In addition to cream of tartar, there are tartaric acid, sodium bicarbonate, calcium and magnesium carbonate and pyrophosphates.

The speed of gas release is a fundamental aspect; if for example it is too fast, the gas will develop before the structure of the dough is sufficiently stiff due to the heat; as a result, the product will quickly swell and then collapse.

As anticipated, the term chemical must not frighten us, given that we are dealing with food additives regulated by law to guarantee consumer safety. Problems could be had ONLY in case of systemic use at high doses (it is always the dose to make the poison).

For example, products leavened with cream of tartar are preferable to those leavened with phosphates, especially if they are consumed by children (phosphates reduce calcium absorption). Sodium bicarbonate, on the other hand, increases the intake of this mineral, often present in excess in the diet.

Video Recipes based on instant yeast

Video Yeast based recipes for desserts