Baker’s yeast, the common name for Saccharomyces cerevisiae, is a strain of yeast used in baking to leaven bread and other baked goods. It is a eukaryotic, single-cell microorganism that feeds on sugars and produces carbon dioxide as a byproduct, which causes the dough to rise. Baker’s yeast is available in both fresh and dry forms, with the dry form being more commonly used due to its longer shelf life. It is a versatile ingredient essential to creating light and fluffy baked goods. Saccharomyces cerevisiae is also used to brew beer and make wine.
What is Baker’s Yeast?
Baker’s yeast is a member of the fungus kingdom. Its scientific name is Saccharomyces cerevisiae, which refers to its nature as “a mold which ferments the sugar in cereal (saccharo-mucus cerevisiae) to produce alcohol and carbon dioxide.”
Yeast is a unicellular organism (single cell). Individual cells appear round to oval. A yeast cell has 6,000 different yeast genes. The genome is made up of 16 chromosomes. The osmotic properties of a yeast cell are due to the selective permeability of the cell wall. This selectivity plays a vital role in controlling the movement of nutrients into a cell. The permeability of the cell wall also permits the release of alcohol and carbon dioxide from the cell during fermentation.
Yeast is asexual and reproduces by budding. The double cell wall may have bud scars caused by budding. There may be up to ten such scars. Once the cell is completely covered in bud scars, it expires. When yeast cells are deprived of food, they can reproduce by sporulation, producing up to four spores each. Yeast cells can survive in spores for extremely long periods, and when later brought into contact with the right conditions, the yeast will return to active life.
How is Baker’s Yeast Produced?
Baker’s Yeast is produced industrially through a process called fermentation. Yeast fermentation involves growing and multiplying the yeast cells in large-scale bioreactors under controlled conditions. Fermentative yeast production employs a carbon source, nitrogen source, minerals, vitamins, pH control agent, and air.
Because molasses is an agro-industrial byproduct rich in sugars, it is commonly used for large-scale production of baker’s yeast. The vitamins and minerals in molasses support yeast growth. Molasses from beet, cane, or a mixture of both can be used. Nitrogen, in the form of ammonia, is a major growth nutrient. Oxygen is provided in the form of filtered air. The obtained yeast is either supplied fresh (cream yeast) or pressed or dried to be used commercially.
Applications in the Food Industry
Yeast is used in the food industry in two primary forms: baker’s yeast and yeast extract. Baker’s yeast primarily acts as a leavening agent, starter culture, and source of protein, vitamins, and minerals. Yeast extract is a concentrated form of the soluble components of yeast cells, produced by breaking down the yeast cells and removing the cell walls to leave behind its soluble components. Yeast extract is a flavor enhancer, fermentation medium, and salt substitute.
Functions of Baker’s Yeast
|Leavening Agent||Saccharomyces cerevisiae is used in baking as a leavening agent, converting the fermentable sugars present in the dough into carbon dioxide. This causes the dough to leaven or rise as the carbon dioxide forms pockets or bubbles. When the dough is baked, it sets, and the pockets remain, giving the baked product a soft and spongy texture.|
|Starter Culture||Saccharomyces cerevisiae is used as a starter culture to obtain fermented products. It carries out fermentation and changes the physicochemical, sensory, and nutritional properties of the food product.|
|Protein Source||Yeast has a high protein content, with approximately 40-50% of its dry weight being protein. This makes it a valuable source of protein for vegetarians, vegans, and individuals with dietary restrictions or preferences that limit their protein intake from animal sources. Additionally, yeast protein is easily digestible and has a high bioavailability, meaning that the body can efficiently absorb and utilize the protein it provides.|
|Vitamin & Mineral Source||Yeast is a good source of minerals. It is particularly rich in minerals such as potassium, magnesium, zinc, and selenium. These minerals are essential for various bodily functions, including maintaining a healthy immune system, supporting nerve function, and promoting proper muscle function. Yeast also contains B vitamins, including thiamine (B1), riboflavin (B2), niacin (B3), and pantothenic acid (B5).|
Functions of Yeast Extract
|Flavor Enhancer||Yeast extract is used as a flavor enhancer in various food products, such as soups, sauces, and savory dishes. It provides a savory umami taste and can be used as a vegetarian alternative to meat-based flavorings. It contains various compounds, such as glutamic acid and nucleotides, contributing to the savory, umami taste and aroma.|
|Fermentation Media||Yeast extract contains various nutrients essential for microbial growth, including amino acids, vitamins, minerals, and nucleotides. These nutrients provide the necessary building blocks for synthesizing proteins, nucleic acids, and other cellular components.|
|Salt Substitute||Yeast extract can provide a savory taste that can help reduce the need for additional salt in specific recipes. It can contribute to a more balanced and flavorful dish when used in moderation.|
|Bakery||Bread, Rolls, Bagels, Buns, Pizza, Scones, etc.|
Properties of Baker’s Yeast
|Physical Form||Powder, Cream, Granules, Cake|
|Color||Cream to Brown|
|Shelf Life||Differs according to product|
|Claims (*Product Specific)||Natural, Kosher*, Halal*, Vegan|
Finger Millet Bread
Here is an example of a finger millet bread formulation table with baker’s yeast along with the weight of ingredients:
|Finger millet flour||100|
|Dry gluten powder||10-20|
|Ascorbic acid||0.005 – 0.015|
|Fungal α amylase||0.001 – 0.005|
|Distilled glycerol monostearate||0.1 – 0.25|
|Sodium stearoyl – 2 – lactylate||0.1 -0.25|
|Calcium propionate||0.2 – 0.5|
|Glacial acetic acid||0.05-0.15|
Source: Google Patents
Baker’s Yeast Formulation Considerations
|Stability||Baker’s yeast in dried form has higher stability compared to cream yeast.|
|Dosage||Dosage ranges from 0.5 to 5 % or more depending on the end product and function.|
|Nutritional Composition||Baker’s yeast contains ~40 % protein, ~41% carbohydrate, 26.9% fiber, 7.6% fat, and 5.6% ash content. A detailed nutritional composition of baker’s yeast can be found here.|
Baker’s yeast, like baking powder and baking soda, leaven baked goods such as breads and cakes. Baking powder and baking soda react chemically to produce the carbon dioxide that makes the baked goods rise. Yeast, however, does not cause a chemical reaction. Instead, the carbon dioxide it produces results from the yeast feeding on the dough.
Aerobic and Anaerobic Respiration
Baker’s yeast can survive and thrive both in the presence and absence of oxygen—it is aerobic and anaerobic. In the presence of oxygen, yeast undergoes aerobic respiration and converts glucose (sources of sugar) and oxygen into carbon dioxide and water. Without oxygen, yeast performs fermentation and can convert carbohydrates into carbon dioxide and alcohol. Yeast obtains more energy when in aerobic respiration than when it is anaerobic.
Activity and Products
When yeast, water, and flour are mixed under the right conditions, the components required for fermentation are present in the form of soluble protein to build new cells and sugar to feed them. Yeast growth happens when reproduction occurs under warm water 30°C / 86°F and nutrients (sugar). The actions of yeast may be shown in a simplified form as follows:
- simple sugar ⇒ ethyl alcohol+carbon dioxide
- C6H12O6 ⇒ 2C2H5OH+2CO2
Fungal secondary metabolites (FSMs) represent a remarkable array of bioactive compounds with potential applications as pharmaceuticals, nutraceuticals, and agrochemicals. Secondary metabolites are protective compounds that prevent abiotic and biotic stresses, i.e., predation, infection, drought, and radiation. These valuable natural products are often difficult to synthesize chemically and are commonly isolated through inefficient extractions from natural biological sources. Yeast secondary metabolites include flavonoids, polyketides, terpenoids, and amino acid derivatives.
Factors Affecting Fermentation
Various factors, including dough ingredients, fermentation conditions, type of yeast strain used, and yeast pre-growth conditions, affect the fermentative performance of yeast cells during dough fermentation.
|Dough Ingredients||In general, Saccharomyces cerevisiae is an acidophilic organism that grows better under acidic conditions. The best pH range for yeast is 4.5-6.0. Bread doughs are generally in the region of 5.5, so using yeast does not usually have an effect. At high pH values of the medium, the internal pH of the cells would show significant variation depending on the external pH, which also affects the metabolic processes and metabolites.|
|pH||The optimum temperature range for yeast to grow and reproduce at the fermentation stage is 27-32°C. Inactivation of yeast occurs between 54-56°C. Yeast’s growth rate and metabolism increase when the temperature is raised from sub-optimal to optimal temperatures and decrease when the temperature rises beyond optimal temperature.|
|Temperature||Supplementation of fermentation media with specific nutrients can enhance the viability and fermentation rate of yeast. Nitrogen sources and minerals (especially key metal ions) are important determinants of yeast performance.|
|Water content||Normal yeasts require a minimum water activity of 0.85 or a relative humidity of 88%.|
|Storage||Loss of yeast activity during storage is associated with temperature fluctuations and moisture intrusion during storage.|
|Nutrients in Media||Supplementation of fermentation media with specific nutrients can enhance the viability and fermentation rate of yeast. Nitrogen sources and minerals (especially essential metal ions) are important determinants of yeast performance.|
S. cerevisiae in Sourdough Fermentation
Sourdough is a bread made by fermenting dough using wild lactobacillus and yeast. It is a naturally leavened bread, which means it doesn’t use commercial yeast to rise. The sourdough microbiome is maintained in a starter used to inoculate dough for bread production. Yeasts, lactic acid bacteria (LAB), and acetic acid bacteria (AAB) in the starter produce the CO2 that leavens the bread. Saccharomyces cerevisiae plays a key role as a leavening agent by producing carbon dioxide through the alcoholic fermentation of sugars, thus increasing loaf volume.
Benefits and Limitations of Using Saccharomyces Cerevisiae
There are a few limitations to using baker’s yeast in bakery products compared to other leavening agents, which should be considered.
- Time: Baker’s yeast requires time to ferment and produce carbon dioxide, which is necessary for bread to rise. This can limit the production process as it takes several hours for the dough to rise and proof.
- Flavor: Baker’s yeast can produce a slightly yeasty flavor in bread. This may or may not be desirable for certain types of bread or culinary preferences.
- Sensitivity to Temperature and pH: Baker’s yeast is sensitive to temperature changes. This can make it challenging to control the fermentation process and achieve consistent results.
- Dependence on Additives: Baker’s yeast often requires the addition of sugar or other additives to promote fermentation. This reliance on additives can limit the ability to produce bread with minimal ingredients or specific dietary restrictions.
Baker’s yeast is available in a variety of different forms. Active dry yeast and instant yeast are the most common commercial baking yeast. Each form has specific advantages over the others.
|Active Dry Yeast||Instant yeast is made using a process similar to active dry yeast, although it is dried more quickly and milled into finer particles. It may contain a higher amount of active cells per granule. It dissolves and starts multiplying faster compared to active dry yeast. Proofing is not necessary for instant yeast. Instant yeast is occasionally supplemented with ingredients like ascorbic acid, a dough conditioner, to speed up the rising process. The shelf life of instant yeast is slightly shorter compared to active dry yeast.|
|Instant Yeast||Rapid-rise yeast is a variant of instant yeast with a finer granule size and quick solubility. Few enzymes and other additives are included to make the dough rise faster. It activates immediately upon being added to the wet formulation and starts the process of leavening quickly. There is considerable debate as to the value of rapid rise yeast. Many baking experts believe it reduces the flavor potential of the finished product.It is generally used for instant mixes and quick baking processes. Using rapid-rise yeast eliminates the need for an additional proofing stage for the dough, which can be immediately shaped after kneading.|
|Rapid Rise Yeast||Yeast cake is prepared by compressing and removing most of the water from the cream yeast. This form also has a lower shelf life.|
|Cream Yeast||Cream yeast is a suspension of yeast cells in a liquid separated from the growth medium. It has high vitality and viability due to minimal processing and quicker use. Higher product volume and reduced fermentation time can be achieved using cream yeast. It isn’t easy to handle and transport. Cream yeast makes it difficult to maintain consistency or reproducibility and has a very low shelf life.|
|Compressed Yeast or Yeast Cake||Yeast cake is prepared by compressing and removing most water from the cream yeast. This form also has a lower shelf life.|
Selective Yeast Strains
The industrial strains of Saccharomyces cerevisiae each have different growth rates, tolerances, growth conditions, and secondary metabolites. Certain strains with desirable properties are used to improve product quality based on the individual formulation requirements.
|Osmotolerant & Halotolerant||Yeast has limited tolerance to inhibitory conditions due to high ethanol concentration. Conventional yeast is a bioethanol producer but has limited tolerance to temperatures above 40°C and high ethanol concentrations. The ethanol tolerance of conventional Saccharomyces cerevisiae ranges from 10-15%. Low ethanol-tolerant strains can have limited usage in ethanol production. Selective strains of Saccharomyces cerevisiae have high ethanol tolerance and can grow in 13% ethanol, but growth is completely prevented at 14% ethanol.|
|Thermotolerant Yeast||Yeast has limited tolerance to inhibitory conditions due to high ethanol concentration. Conventional yeast is a bioethanol producer with limited tolerance to temperatures above 40°C and high ethanol concentrations. The ethanol tolerance of conventional Saccharomyces cerevisiae ranges from 10-15%. Low ethanol-tolerant strains can have limited usage in ethanol production. Selective strains of Saccharomyces cerevisiae have high ethanol tolerance and can grow in 13% ethanol, but growth is completely prevented at 14% ethanol.|
|Ethanol Tolerant||The optimum temperature range for yeast fermentation is between 90-95˚F (32-35˚C). Every degree above this range depresses fermentation. Thermotolerance is the transient ability of yeast cells to survive at higher temperatures. Thermotolerant yeast strains can survive at temperatures above 40°C. Genetic adaptations to high-temperature resistance can also improve tolerance to other stresses.|
Genetically Modified Yeast
Yeast strains can be genetically engineered for better growth characteristics, nutrition, tolerance, and end-product properties. However, although numerous industrial recombinant yeasts have been constructed, using genetically modified (GM) yeast for baking and brewing is uncommon.
Effects of Baker’s Yeast on Physicochemical Properties
- Dough Volume: The carbon dioxide produced by the yeast during fermentation creates air pockets within the dough. These air pockets expand and cause the dough to rise, resulting in increased volume. One study showed an increase in dough volume of up to 240% at 37°C.
- Texture: During fermentation, the yeast produces carbon dioxide, which creates air pockets and contributes to the light and airy texture of bread.
Effects of Baker’s Yeast on Sensory Properties
- Aroma: Baker’s yeast contributes to the characteristic aroma of freshly baked bread. During fermentation, the yeast produces volatile compounds that give bread its distinct smell. This aroma is often described as warm, nutty, and slightly sweet.
- Flavor: Baker’s yeast contributes to the taste of baked products. Yeast can add a subtle sweetness to the flavor profile of the bread. Yeast produces a variety of flavorful byproducts, such as esters and higher alcohols, that contribute to the taste and aroma of baked goods.
Effects of Baker’s Yeast on Nutritional Properties
- Protein Content: Baker’s yeast is a rich source of protein. The protein content of baker’s yeast varies, depending on the strain and processing methods, but it typically contains around 40-50% protein on a dry weight basis. This makes baker’s yeast a valuable source of dietary protein, especially for individuals following a vegetarian or vegan diet. The proteins in baker’s yeast are a mixture of enzymes, structural proteins, and metabolic proteins, which contribute to the functionality and nutritional value of the yeast. Studies report that the percentage of proteins found for brewing yeast ranges between 32-62%.
- Effect on Gut Microbiota: Yeast cell wall has been reported to have prebiotic activity, which improves the microbiota composition of the human gut. Additionally, yeast mannoproteins are proposed as para probiotics with antimicrobial and prebiotic properties.
- Effect on Anti-Nutritional Factors in Food: Baker’s yeast has been widely used to reduce anti-nutritional factors of diet through fermentation and phytic acid degradation with phytase. In a study, fermentation using yeast reduced the content of two anti-nutritional factors, intact glucosinolates and 3-butyl isothiocyanate, by 51.60–66.04% and 55.21–63.39%, respectively.
- Fiber & Mineral Content: β-glucan is a polysaccharide in the form of fiber that is found in baker’s yeast. Yeast cell walls contain about 30% of β-glucans of dry weight. Baker’s yeast is also high in minerals, including magnesium, phosphorus, potassium, calcium, and sodium.
Safety and Regulatory Considerations
|FDA Information||The FDA includes dried yeast (Saccharomyces cerevisiae) in multipurpose food additives. It can be safely used in food products. Baker’s yeast glycan and baker’s yeast protein can also be used as food additives for direct consumption. Baker’s yeast extract has a GRAS status by the FDA and can be used in food not exceeding 5% dosage.|
|EU Information||EU Regulation 2017/2470 includes UV-treated baker’s yeast (Saccharomyces cerevisiae) as an authorized novel food.The use of UV-treated baker’s yeast (Saccharomyces cerevisiae) has been extended to additional food categories, namely, pre-packed fresh or dry yeast for home baking and food supplements without indication of maximum permitted levels.|
Health Effects of Baker’s Yeast
- Nutritional Value: Baker’s yeast is a rich source of essential nutrients such as thiamine, riboflavin, niacin, folate, proteins, minerals such as zinc and selenium, and dietary fiber. These nutrients are important for overall health and play a crucial role in various bodily functions.
- Immune Support: Certain compounds in baker’s yeast, such as beta-glucan, have been found to enhance immune function. Beta-glucan stimulates the activity of immune cells, boosts the production of antimicrobial compounds, and may help reduce the risk of infections.
- Gut Health: Baker’s yeast can provide prebiotic & probiotic benefits by improving gut health.
- Anti-inflammatory Effects: Some studies have suggested that S. cerevisiae may have anti-inflammatory properties. Cerevisiae var. boulardii reduced the levels of pro-inflammatory cytokines and NF-κB signaling.
Safety & Toxicity of Baker’s Yeast
S. cerevisiae is currently classified as a class 1 containment organism under the NIH Guidelines mainly based on the extensive history of safe use. Factors associated with the development of disease states in fungi have been reviewed.
Fun Facts About Baker’s Yeast
- Baker’s yeast has been used in biotechnology to produce various recombinant proteins, including insulin and vaccines. Its ability to efficiently express foreign genes makes it valuable in the pharmaceutical and biotech industries.
- Saccharomyces cerevisiae has one of the smallest known genomes of any eukaryote, yet it’s highly functional. Its simplicity has made it a model organism for genetic and molecular biology research.
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- PubMed Central – Article PMC9998214
- PubMed Central – Article PMC7582661
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- Massey University – Factors Affecting the Activity of Bakers Yeast
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