Noah Vinter
Alcoholic fermentation, also known as ethanol fermentation, is a biological process that converts sugars into alcohol and carbon dioxide through the action of microorganisms, primarily yeast or bacteria. This process has been used for millennia and is pivotal to the brewing industry, as it is responsible for producing the ethanol (alcohol) found in beer, wine, and spirits. The by-products of fermentation include heat, carbon dioxide, water, and alcohol, with carbon dioxide being essential to the production of carbonated beverages and bread-making. The type of yeast used in fermentation can vary depending on the desired characteristics of the final product, with different strains producing different flavor by-products.
| Characteristics | Values |
|---|---|
| Fermentation by-product | Carbon dioxide |
| Fermentation process | Anaerobic |
| Fermentation agent | Yeast |
| Yeast type | Saccharomyces cerevisiae (ale yeast) or Saccharomyces pastorianus (lager yeast) |
| Yeast function | Converts sugars into alcohol and carbon dioxide |
| Yeast tolerance | High concentrations of sugar, alcohol, SO2, low pH, low temperatures, and high pressures |
| Yeast benefits | Produces low amounts of undesirable compounds, converts sugars to alcohol and flavor-active compounds |
| Other fermentation microorganisms | Bacteria, fungi, Zymomonas mobilis, Leuconostoc bacteria, Escherichia, Enterobacter |
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What You'll Learn
Yeast's role in fermentation
Yeast plays a vital role in the production of all alcoholic beverages and fermented foods. Fermentation is a natural process that has been used for thousands of years to produce a variety of foods and drinks. The process involves the use of microorganisms, especially yeasts and some bacteria, to convert sugars and other carbohydrates into organic acids, alcohols, and gases.
In the context of alcoholic fermentation, yeast multiplies through budding and converts sugars, such as glucose, fructose, and sucrose, into ethanol and carbon dioxide. Yeast is indispensable for this process, and its role was first understood by French inventor Charles Cagniard de la Tour in 1835. Later, in the 1850s and 1860s, French chemist Louis Pasteur became the first scientist to study fermentation, demonstrating that it was performed by living cells and that yeast transformed glucose into ethanol.
Different strains of yeast have varying alcohol tolerances, and this property is leveraged by brewers and winemakers to produce beverages with different alcohol contents. For example, wines typically contain higher ethanol concentrations than beers. Additionally, the selection of yeast strains is crucial for maintaining the sensory quality of the final product. Non-Saccharomyces yeasts, once considered contaminants, are now recognized for their ability to influence the sensory profile of wines and beers, producing high levels of aromatic compounds.
In beer brewing, two types of yeast are commonly used: S. cerevisiae for ales and S. pastorianus for lagers. Cider, another popular alcoholic beverage, can be produced through spontaneous fermentation by autochthonous yeasts or with selected S. cerevisiae strains. The production of beer, a highly consumed beverage worldwide, relies on yeast to convert cereal-derived sugars into ethanol and carbon dioxide, with the latter contributing to the rising of the dough.
Overall, yeast plays a pivotal role in fermentation by driving the conversion of sugars into ethanol and carbon dioxide, a process essential for producing alcoholic beverages and certain foods, such as bread.
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Alcohol by-products
Alcoholic fermentation, also known as ethanol fermentation, is a biological process that converts sugars and other carbohydrates into alcohol and carbon dioxide through the action of microorganisms, primarily yeast or bacteria. This process is commonly used in the production of alcoholic beverages, such as wine, beer, and spirits. During fermentation, yeast cells break down sugars and starch into ethanol and carbon dioxide, which are considered by-products of fermentation.
The yeast species Saccharomyces cerevisiae is the most commonly used yeast in the alcohol industry, particularly in beer and wine production. This yeast species is favoured due to its remarkable tolerance to high concentrations of sugar, alcohol, and preservatives, as well as its ability to produce low amounts of undesirable compounds. Different strains of this yeast can also be selected to produce different flavour by-products, allowing for a range of characteristics in the final product.
In addition to ethanol and carbon dioxide, other by-products of the fermentation process include water, heat, and hundreds of secondary metabolites that influence the aroma and taste of the beverage. These secondary metabolites are produced by different yeast strains, giving each beer a unique flavour profile. For example, lager yeast, or Saccharomyces pastorianus, is a bottom-fermenting yeast that can ferment the sugar melibiose, while ale yeast, or Saccharomyces cerevisiae, is a top-fermenting yeast that cannot.
The fermentation process also plays a crucial role in bread-making, where the carbon dioxide produced by yeast causes the dough to rise, creating a light and airy texture. Additionally, fermentation is used in the production of biofuels, such as ethanol fuel, and in the treatment of agro-industrial effluents to reduce waste toxicity.
Overall, the by-products of alcohol fermentation, particularly ethanol and carbon dioxide, are pivotal to the brewing industry, as they are the main components of alcoholic beverages and influence the flavour, aroma, and texture of the final product.
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Fermentation and distillation
There are several types of yeast used in fermentation, including S. cerevisiae, which is used in ales, and S. pastorianus, which is used in lagers. Yeast functions best in a slightly acidic medium, and the acidity of the mixture must be checked and adjusted if needed. The yeast is then added, and the final dilution is made. The concentration of sugars is adjusted so that the yeast fermentation will produce a finished mixture containing between 7 and 9% alcohol. Fermentation at lower temperatures takes longer, and if it continues past the optimal period, it will be adversely affected by bacterial action.
Distillation is the process of extracting fermented beverages and separating the alcohol from them. Distillation is used to produce alcoholic beverages with a higher alcohol content than those produced by fermentation, such as whiskey, vodka, and rum. Distillation involves heating the fermented beverage to boil the alcohol and convert it into vapour. The vapour is then collected and cooled, turning it back into a liquid. This liquid is then collected in separate containers.
Fermentation plays a crucial role in the distillation process, as it is the stage where yeast produces the alcohol that will be extracted through distillation. A good fermentation program is essential for the success of the distillation process, as it greatly impacts the final outcome. The majority of craft distillers use dry yeast due to its ease of handling and convenience. The yeast goes through a "lag phase" where it adjusts to the aqueous environment, followed by the "stationary phase" where most sugars have been consumed, and finally, the yeast is stuck in a toxic, high-concentration alcohol environment.
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Fermentation in baking
The use of fermentation in baking bread can be traced back to the ancient Egyptians in 4000 BCE. Fermentation is a biological process that converts sugars such as glucose, fructose, and sucrose into cellular energy, producing ethanol and carbon dioxide as by-products. In the context of bread baking, fermentation allows dough to rise and develop a unique flavour and texture.
During fermentation, yeast organisms, such as Saccharomyces cerevisiae, consume sugars in the dough and produce ethanol and carbon dioxide. The carbon dioxide forms bubbles in the dough, causing it to expand into a foam. The ethanol produced during fermentation evaporates during the baking process, leaving less than 2% ethanol in the final product.
The process of fermentation in bread baking typically involves mixing flour, yeast, and water, which can be done as an optional preferment step or directly with the rest of the dough composition. This step can last for up to 8 hours in artisan breads. After the dough is punched, a second fermentation takes place, followed by proofing, which can last from 1 hour to 1 day.
The rate of fermentation is influenced by temperature, with lower temperatures slowing down the process and higher temperatures producing undesirable aromas and excessive acid buildup. Therefore, the ideal temperature range for fermentation in bread baking is between 95–113°F (35–45°C).
By extending the duration of dough fermentation, bakers can improve dough development and enhance the shelf life of the bread. This extended fermentation process is considered an effective alternative to traditional dough conditioners, allowing bakers to produce clean-label bakery products.
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Natural vs cultivated yeasts
Yeast is an essential part of the fermentation process, converting sugars into alcohol. The most common yeast used in fermentation belongs to the genus Saccharomyces cerevisiae. This species is well-suited to winemaking due to its tolerance for relatively high levels of alcohol and its ability to withstand sulphur dioxide, which most non-Saccharomyces yeasts cannot.
Natural Yeasts
Also known as wild or indigenous yeasts, these occur naturally in the air or on surfaces. They are often found on grapes in vineyards, but they can also come from winery equipment or even the floor. Fermentation with natural yeasts is spontaneous and unpredictable, and it can take longer for wild yeast to colonise. Wild yeasts also have a low resistance to alcohol, with many types unable to perform once alcohol levels reach 6%. A frequent by-product of wild yeast is unusual or odd odours and flavours, which can add to the complexity of the wine.
Cultivated Yeasts
Also referred to as inoculated yeasts, these are commercially available cultured yeasts. Cultivated yeasts are reliable and allow for a rapid onset of fermentation. They are often chosen by winemakers because they can provide specific characteristics to the wine. Cultivated yeasts also come in larger doses than wild yeasts, reducing the risk of infection from other spoilage organisms and oxidation.
Pros and Cons
Spontaneous fermentation with natural yeasts can add a unique character and distinctiveness to the wine, but it requires greater care and attention from the winemaker. On the other hand, cultivated yeasts are a more controlled option, providing consistency and specific characteristics to the wine. However, some may argue that this comes at the cost of losing the interesting, unpredictable qualities that natural yeasts can bring.
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Frequently asked questions
Carbon dioxide is the alcohol fermentation by-product that is pivotal to the brewing industry.
Ethanol fermentation, also known as alcoholic fermentation, is a biological process that converts sugars into alcohol and carbon dioxide through the action of microorganisms, primarily yeast or bacteria.
Yeast organisms consume sugars and produce ethanol and carbon dioxide as waste products. Yeast can also produce ethanol under aerobic conditions if provided with the right nutrition.
Examples of ethanol fermentation in food and drinks include wine, beer, spirits, cider, perry, bread, and sauerkraut.
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