Someone once said that "without yeast, there is no life of wine", and many people see yeast as just converting sugar into alcohol, but is this really the case? Yeast is a small substance, but it can penetrate into every aspect of wine, regardless of appearance, aroma, taste, nutrition and other aspects. "Water can carry boats, but also can cover boats", yeast can add a lot of good side to wine, but it will also bring fatal harm to wine. Today, let's take stock of the "basic feelings" of yeast and wine.
1. The type of yeast
Yeast is divided into Saccharomyces cerevisiae (Saccharomyces) and non-Saccharomyces cerevisiae. Saccharomyces cerevisiae plays a pivotal role in wine, converting the sugars in grapes into alcohol and carbon dioxide, while converting substances such as amino acids into flavor substances such as alcohols and esters through a series of reactions.
Non-Saccharomyces cerevisiaesis (Non-Saccharomyces cerevisiae) is unable to complete wine fermentation alone, with poor alcohol resistance, low fermentation power, short survival time and high acid production characteristics, previously often considered to be the "black sheep" of winemaking, and odor substances (acetate, acetaldehyde and hydrogen sulfide, etc.) and wine quality corruption, but now more and more studies show that non-Saccharomyces cerevisiae can also have a positive impact on wine.
How to distinguish between Saccharomyces cerevisiae and non-Saccharomyces cere
In addition to the above classifications, yeast can also be divided into natural yeast and artificial yeast. Natural yeast is the yeast that attaches to the skin of the grape and can also initiate the fermentation of the wine. Artificial yeast refers to the yeast that humans cultivate for the specific needs of fermentation. Saccharomyces cerevisiae and non-Saccharomyces cerevisiae can belong to both natural and artificial yeasts.
2. The influence of yeast on the appearance of grape fruits
From the time the grapes are ripe to the harvest, the survival of yeast has a certain biological inhibition effect on mold, and to a certain extent, the quality of the grape fruit can be maintained. For example, the lemon Kloeckera Apiculata on the surface of grapes inhibits fruit rot caused by the fungus. Candida guilliermondii has a significant inhibitory effect on the gray grape spore mold and Aspergillus niger that can cause grape rot.
3. The influence of yeast on the color of wine
The color of the wine is mainly determined by the type and content of anthocyanins, usually the higher the anthocyanin content, the darker the color of the wine. In the fermentation process, the cell wall of yeast has an adsorption effect on anthocyanins, and different yeasts have different adsorption capacity of anthocyanins on wine, but they are easy to absorb acyl anthocyanins, which is also the main mechanism of yeast affecting the color of wine. Thus yeast can also affect the color of the wine, when the greater the adsorption capacity of the yeast cell wall, the lighter the color of the wine.
4. The influence of yeast on the fermentation process of wine
During alcoholic fermentation, yeast converts the sugars in the fruit into alcohol and carbon dioxide, initiating the process of wine fermentation. The fermentation capacity of different yeast species will vary, with some fermenting fast and some fermenting slowly. Slow fermentation delays the fermentation of the wine, so that the longer the skin, juice and seed are macerated, the darker the color of the wine, the more tannins and other polyphenols it contains, and the more complex the taste. However, in extreme cases, the fermentation rate of yeast is slow, which may lead to hazards such as fermentation abort.
5. The influence of yeast on the aroma of wine
Wine aromas are divided into 3 categories: variety aromas, fermentation aromas and aging aromas. Variety aroma mainly refers to the aromatic substances in the grape fruit, related to grape raw materials; fermentation aroma is mainly in the process of alcoholic fermentation, produced by yeast metabolism of aromatic substances; aging aroma is the aromatic substance generated by a series of redox reactions during the aging process of wine.
More than 1,000 volatile compounds have been detected in wine, more than 400 of which are produced during yeast fermentation. During alcoholic fermentation, yeast converts 95% of the sugars in grape juice into ethanol and carbon dioxide, 1% of the sugars into cellular matter, and the remaining 4% into other end products, including glycerol, volatile and non-volatile organic acids, higher alcohols, and less volatile esters.
The volatile substances generated during yeast alcoholic fermentation mainly include acetate and ethyl esters (floral and fruity aromas), higher alcohols (almonds and floral aromas), medium and long chain volatile acids (cheese and sweat flavor), aldehydes (fruit and nut flavors), etc. The type, proportion and balance of these substances affect the sensory quality of wine and determine the quality of wine.
(1) Higher alcohols: alcohols are the main substances that constitute the aroma of wine fermentation, and they are mainly the products of amino acid or sugar metabolism during yeast alcohol fermentation. The right amount of alcohol can bring good aromas to the wine, they can make the aroma of the wine more complex and intense, but most alcohols have unpleasant aromas, which may have a negative contribution to the aroma quality of the wine. The higher alcohols produced by yeast are: isobutanol, isoamyl alcohol, 2-phenethyl alcohol, and 1-propanol. Isobutanol has the mellow aroma of fusel oil, isoamyl alcohol has a bitter almond flavor, 2-phenethyl alcohol has rose, rose and pollen aromas, and 1-propanol has a fragrance and alcohol flavor.
(2) Esters: Esters have the aroma of flowers or fruits, which is beneficial to the aroma quality of wine. The main factors affecting the composition and content of esters in wine are the chemical composition of grape juice and the brewing process used, and when the above factors are determined, the selected yeast strain will also have an effect on the influence of ester composition in wine. The esters produced by yeast mainly include fatty acid ethyl esters and acetates. Fatty acid ethyl esters mainly include ethyl butyrate (fruity and strawberry flavor), ethyl caproate (green apple fragrance, strawberry fragrance and fennel), ethyl caprylate (fruity and fennel), ethyl isobutyrate (fruity and strawberry fragrance) and ethyl isovalerate (banana and sweet fruit) and so on. Acetates mainly include ethyl acetate (fruity, ester flavor), hexyl acetate (pear flavor), isoamyl acetate (banana flavor) and -2-phenylethyl acetate (floral) and so on.
(3) Volatile acid: organic acid is the main substance that maintains the balance of the wine body and the refreshing characteristics of the taste, such as the appropriate acid content can make the wine have a fresh fruit aroma, which can modify the taste and taste of the wine. The composition and content of acids are also affected by the yeast strain chosen. The volatile acids produced by yeast mainly include acetic acid (vinegar taste), propionic acid (sheep fishy taste), butyric acid (spoiled cheese taste), isobutyric acid (fat taste), caproic acid (cat urine taste and sweat odor), prunic acid (cheese taste, putrefaction and astringency) and sunflower acid (unpleasant fat taste). Although these volatile acids have an unpleasant taste, the ethyl esters they form, with excellent aroma and pleasant aroma, are an important guarantee of the aroma quality of wines.
Therefore, the high alcohols, esters and volatile acids produced by yeast during fermentation are important components of wine aromas, thus playing a vital role in the aroma of wine.
6. The influence of yeast on the taste of wine
During the brewing process of sherry, the yeast forms a cream-like film on the surface of the sherry, also known as "flor". The alcohol, oxygen and other wine components in these yeast diet liquors metabolize substances such as carbon dioxide and acetaldehyde, of which acetaldehyde can give sherry wine-like aromas. During this process, the tannins and polyphenols in sherry slowly oxidize, resulting in a softer and more delicate taste, while emitting slight "oxidizing" aromas, almonds and walnuts.
During the normal static wine fermentation process, yeast will metabolize glycerol and organic acids, which can increase the mellowness and acidity of the wine. Therefore, yeast also has an impact on the taste of the wine.
7. The influence of yeast on the nutritional value of wine
Resveratrol in wine has anti-cancer, antioxidant and anti-aging effects, and its sources are mainly in three aspects: one is macerated from the peel during fermentation, the other is metabolized by Saccharomyces cerevisiae (coumyl Coenzyme A is synthesized through the phenylpropanolamine hydrochloride route, and then synthesized with malonate monoacyl-coenzyme A), and the third is the malate lactic acid fermentation process, which is decomposed by some resveratrol oligomers and flavanol and condensed tannins of resveratrol.
Because yeast fermentation can produce resveratrol, it can increase the nutritional value and efficacy of wine.
8. The effect of yeast autolysis on wine
Usually, during the bottle aging of sparkling wines, especially Champagne, yeast releases flavor substances by autolysis. Yeast is a single-cell microorganism, the main product after autolysis is still derived from the yeast cell itself constituent substances, such as dextrans, mannans, proteins, chitin, lipids and inorganic substances in the cell wall, as well as various substances in the cell fluid, they will release and produce a large number of yeast polysaccharides (mannose proteins), amino acids, polypeptide substances, nucleotides and fatty acids in the cell wall, of which mannose proteins and polypeptides have a prominent impact on the sensory quality of wine.
(1) Soften the tannins and improve the fullness and roundness of the taste: yeast polysaccharides can obviously cover up the astringency of the wine, reduce the bad feeling of bitterness and raw greenness of the wine, thereby increasing the roundness of the wine and the delicacy of the tannins, so that the wine body is full and mellow.
(2) Improve tartaric acid stability: Mannose protein hinders the mutual polymerization and crystallization between tartaric acid and tannins through the "wrapping" of fine grains, thereby minimizing the risk of tartar precipitation.
(3) Improve wine protein stability: between mannose protein and unstable protein in wine, a new stabilization system is established through physicochemical action, thereby reducing the degree of polymerization between unstable proteins, thereby improving the stability of proteins in wine.
(4) Improve and enhance the stability of polyphenols in wine: mannose proteins in polysaccharides and polyphenols such as tannins and pigments have a certain binding capacity, and the interaction between them constitutes a stable covalent structure, which can ensure the stability of tannins and pigments in wine.
(5) It can improve the stability and complexity of aroma: the combination of mannose protein and some aromatic substances in wine changes its own structure, resulting in new aromatic substances, thereby enriching the aroma characteristics. Mannose protein contributes to the release of aromatic substances in wine, while at the same time can bind the performance of some undesirable aromatic substances, which is conducive to improving the aroma characteristics of wines.
(6) Balance the sensory properties of alcohol. Mannose protein promotes the binding of ethanol molecules and water molecules in the solution, thereby reducing the taste and sensory stimulation of alcohol, improving the sensory quality of distilled wine and wine on the palate, making it more coordinated and balanced.
(7) Polypeptides affect the taste of wine: polypeptides containing phenylalanine, tyrosine and leucine are the main source of wine bitterness, while polypeptides rich in glycine, alanine and serine give wine a sweet and mellow taste, and peptides containing asparagine and aspartic acid may enhance the sour taste of wine.
(8) After the yeast is self-dissolving, a good wine puree will continue to release glutathione molecules, which have strong antioxidant properties, and can effectively stabilize the pigment substances in the wine when aging, and can also cover up some vulcanized odors.
9. The influence of special artificial yeast on wine
Yeast that is carefully cultivated according to the needs of fermentation is called artificial yeast. General artificial yeast includes sugar-tolerant yeast, heat-tolerant yeast and alcohol-resistant yeast.
Sugar-resistant yeast: This type of yeast has the ability to resist high osmotic pressure, can survive in grape juice with high sugar content, does not produce a large amount of acetic acid, and also has a strong ester production capacity, enhancing the aroma of wine such as floral and fruity aromas. For example, Tourlaspora delbrueckii (Tourlaspora delbrueckii) in the brewing process of guiss and ice wine.
Heat-resistant yeast: This type of yeast can tolerate higher fermentation temperatures, is not easy to cause fermentation to stop, has the ability to directly convert sugar into lactic acid, and can improve the round taste of wine.
Alcohol-resistant yeast: This type of yeast can survive at high alcohol levels, forming a caramel-flavored tetrahydropyridine, clove bacon flavored 4-ethylphenol and sweaty isovaleric acid, etc., these volatile substances can increase the complexity of wine in a reasonable concentration, but after excessive amounts, there will be animal fur and pungent taste.
10. The influence of a variety of yeasts on wine
In the fermentation process, the use of 1 kind of yeast for fermentation, usually the formation of secondary metabolites such as higher alcohols, esters and volatile acids and other types and content is relatively single, and in the fermentation process, the addition of 2 or 3 kinds of yeast at the same time fermentation, the corresponding higher alcohols, esters and volatile acids and other types and content will increase accordingly, so that the aroma of the wine is more intense, more complex. Nowadays, many wineries sometimes use this method in order to produce complex and full-bodied boutique wines.
11. Adverse effects of yeast on wine
(1) Sacrosis: Some non-Saccharomyces cerevisiae such as Pichia and Candida can survive the alcoholic fermentation process and eventually enter the wine, if these corrupt yeasts are not controlled, it may lead to yeast disease in wine. Contamination caused by the rotten yeasts in the genus Red Yeast, Bouquet yeast, Pichia yeast, combined yeast, Candida saccharomyces, Candida saccharomyces cerevisiae, etc. can make the wine deteriorate and lose color, aroma and taste, and can also make the liquid turbid, bubbles, form a film, change color and emit abnormal odors.
(2) Fermentation suspension: When the alcohol content in the wine exceeds 17 degrees or the fermentation temperature exceeds 30 degrees, the yeast will lose its fermentation ability, and the alcoholic fermentation of the wine will be suspended, resulting in wine brewing failure. Some yeasts are intolerant of alcohol and sweetness, which can also cause wine fermentation to be suspended, resulting in losses.
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