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Fermentation in winemaking

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The process offermentation in winemakingturnsgrape juiceinto an alcoholic beverage. Duringfermentation,yeaststransform sugars present in the juice intoethanolandcarbon dioxide(as aby-product). Inwinemaking,the temperature and speed of fermentation are important considerations as well as the levels ofoxygenpresent in themustat the start of the fermentation. The risk ofstuck fermentationand the development of severalwine faultscan also occur during this stage, which can last anywhere from 5 to 14 days forprimary fermentationand potentially another 5 to 10 days for asecondary fermentation.Fermentation may be done in stainless steel tanks, which is common with many white wines likeRiesling,in an open wooden vat, inside awine barreland inside thewine bottleitself as inthe productionof manysparkling wines.[1][2]

Fermentingmust

History

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See also:History of wine

The natural occurrence of fermentation means it was probably first observed long ago by humans.[3]The earliest uses of the word "fermentation" in relation to winemaking was in reference to the apparent "boiling" within the must that came from theanaerobic reactionof the yeast to thesugarsin the grape juice and the release of carbon dioxide. TheLatinferveremeans, literally,to boil.In the mid-19th century,Louis Pasteurnoted the connection between yeast and the process of the fermentation in which the yeast act as catalyst and mediator through a series of a reaction that convert sugar into alcohol. The discovery of theEmbden–Meyerhof–Parnaspathway byGustav Embden,Otto Fritz MeyerhofandJakub Karol Parnasin the early 20th century contributed more to the understanding of the complex chemical processes involved in the conversion of sugar to alcohol.[4]In the early 2010s, New Jersey based wine tech companyGOfermentorinvented an automated winemaking device that ferments in single-use liners similar to thesingle-use bioreactor.[5][6]

Process

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See also:Yeast in winemaking
"Bloom", visible as a dusting on the berries

In winemaking, there are distinctions made betweenambient yeastswhich are naturally present in wine cellars, vineyards and on the grapes themselves (sometimes known as a grape's "bloom" or "blush" ) andcultured yeastwhich are specifically isolated and inoculated for use in winemaking. The most commongeneraof wild yeasts found in winemaking includeCandida,Klöckera/Hanseniaspora,Metschnikowiaceae,PichiaandZygosaccharomyces.Wild yeasts can produce high-quality, unique-flavored wines; however, they are often unpredictable and may introduce less desirable traits to the wine, and can even contribute to spoilage. Few yeast, and lactic and acetic acid bacterial colonies naturally live on the surface of grapes,[7]but traditional wine makers, particularly in Europe, advocate use of ambient yeast as a characteristic of the region'sterroir;nevertheless, many winemakers prefer to control fermentation with predictable cultured yeast. The cultured yeasts most commonly used in winemaking belong to theSaccharomyces cerevisiae(also known as "sugar yeast" ) species. Within this species are several hundred differentstrainsof yeast that can be used during fermentation to affect the heat or vigor of the process and enhance or suppress certain flavor characteristics of thevarietal.The use of different strains of yeasts is a major contributor to the diversity of wine, even among the same grape variety.[8]Alternative, non-Saccharomyces cerevisiae,yeasts are being used more prevalently in the industry to add greater complexity to wine. After a winery has been in operation for a number of years, few yeast strains are actively involved in the fermentation process. The use of active dry yeasts reduces the variety of strains that appear in spontaneous fermentation by outcompeting those strains that are naturally present.[9]

The addition of cultured yeast normally occurs with the yeast first in a dried or "inactive" state and is reactivated in warm water or diluted grape juice prior to being added to themust.To thrive and be active in fermentation, the yeast needs access to a continuous supply ofcarbon,nitrogen,sulfur,phosphorusas well as access to variousvitaminsandminerals.These components are naturally present in the grapemustbut their amount may be corrected by adding nutrients to the wine, in order to foster a more encouraging environment for the yeast. Newly formulated time-release nutrients, specifically manufactured for wine fermentations, offer the most advantageous conditions for yeast.Oxygenis needed as well, but in wine making, the risk ofoxidationand the lack of alcohol production from oxygenated yeast requires the exposure of oxygen to be kept at a minimum.[10]

Dry winemaking yeast (left) and yeast nutrients used in the rehydration process to stimulate yeast cells.

Upon the introduction of active yeasts to the grape must,phosphatesare attached to the sugar and the six-carbon sugarmoleculesbegin to be split into three-carbon pieces and go through a series ofrearrangement reactions.During this process, thecarboxyliccarbon atom is released in the form of carbon dioxide with the remaining components becomingacetaldehyde.The absence of oxygen in thisanaerobicprocess allows the acetaldehyde to be eventually converted, by reduction, toethanol.During the conversion of acetaldehyde, a small amount is converted, by oxidation, toacetic acidwhich, in excess, can contribute to the wine fault known asvolatile acidity(vinegar taint). After the yeast has exhausted its life cycle, they fall to the bottom of the fermentation tank as sediment known aslees.[11]Yeast ceases its activity whenever all of the sugar in must has been converted into other chemicals or whenever the alcohol content has reached 15% alcohol per unit volume; a concentration strong enough to halt the enzymatic activity of almost all strains of yeast.[12]

Other compounds involved

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Themetabolismofamino acidsand breakdown of sugars by yeasts has the effect of creating other biochemical compounds that can contribute to the flavor andaroma of wine.These compounds can be considered "volatile"likealdehydes,ethyl acetate,ester,fatty acids,fusel oils,hydrogen sulfide,ketonesandmercaptansor "non-volatile" likeglycerol,acetic acid andsuccinic acid.Yeast also has the effect during fermentation of releasingglycoside hydrolasewhich canhydrolysethe flavor precursors ofaliphatics(a flavor component that reacts withoak),benzenederivatives,monoterpenes(responsible for floral aromas from grapes likeMuscatandTraminer),norisoprenoids(responsible for some of the spice notes inChardonnay), andphenols.

Some strains of yeasts can generate volatilethiolswhich contribute to the fruity aromas in many wines such as thegooseberryscent commonly associated withSauvignon blanc.
Brettanomycesyeasts are responsible for the "barnyard aroma" characteristic in some red wines likeBurgundyandPinot noir.[13]

Methanol is not a major constituent of wine. The usual concentration range is between 0.1 g/liter and 0.2 g/liter. These small traces have no adverse effect on people and no direct effect on the senses.[14]

Winemaking considerations

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Carbon dioxide activity is visible during the fermentation process in the form of bubbles in the must.

During fermentation, there are several factors that winemakers take into consideration, with the most influential to ethanol production being sugar content in the must, the yeast strain used, and the fermentation temperature.[15]The biochemical process of fermentation itself creates a lot of residualheatwhich can take the must out of the ideal temperature range for the wine. Typically, white wine is fermented between 18–20 °C (64–68 °F) though a wine maker may choose to use a higher temperature to bring out some of the complexity of the wine. Red wine is typically fermented at higher temperatures 20–30 °C (68–86 °F). Fermentation at higher temperatures may have adverse effect on the wine in stunning the yeast to inactivity and even "boiling off" some of the flavors of the wines. Some winemakers may ferment their red wines at cooler temperatures, more typical of white wines, in order to bring out more fruit flavors.[11]

To control the heat generated during fermentation, the winemaker must choose a suitable vessel size or else use a cooling device. Various kinds of cooling devices are available, ranging from the ancientBordeauxpractice of placing the fermentation vat atop blocks of ice to sophisticated fermentation tanks that have built-in cooling rings.[16]

A risk factor involved with fermentation is the development of chemical residue and spoilage which can be corrected with the addition ofsulfur dioxide(SO2), although excess SO2can lead to a wine fault. A winemaker who wishes to make a wine with high levels ofresidual sugar(like adessert wine) may stop fermentation early either by dropping the temperature of the must to stun the yeast or by adding a high level of alcohol (likebrandy) to the must to kill off the yeast and create afortified wine.[11]

The ethanol produced through fermentation acts as an important co-solvent to the non-polar compound that water cannot dissolve, such as pigments from grape skins, giving wine varieties their distinct color, and other aromatics. Ethanol and the acidity of wine act as an inhibitor to bacterial growth, allowing wine to be safely kept for years in the absence of air.[17]

Other types of fermentation

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A California Chardonnay that shows it has been barrel fermented.

In winemaking, there are different processes that fall under the title of "Fermentation" but might not follow the same procedure commonly associated with wine fermentation.

Bottle fermentation

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Bottle fermentation is a method ofsparkling wine production,originating in theChampagneregion where after thecuveehas gone through a primary yeast fermentation the wine is then bottled and goes through a secondary fermentation where sugar and additional yeast known asliqueur de tirageis added to the wine. This secondary fermentation is what creates the carbon dioxide bubbles that sparkling wine is known for.[18]

Carbonic maceration

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The process ofcarbonic macerationis also known aswhole grape fermentationwhere instead of yeast being added, the grapes fermentation is encouraged to take place inside the individual grape berries. This method is common in the creation ofBeaujolaiswine and involves whole clusters of grapes being stored in a closed container with the oxygen in the container being replaced with carbon dioxide.[19]Unlike normal fermentation where yeast converts sugar into alcohol, carbonic maceration works by enzymes within the grape breaking down the cellular matter to formethanoland other chemical properties. The resulting wines are typically soft and fruity.[20]

Malolactic fermentation

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Instead of yeast,bacteriaplay a fundamental role inmalolactic fermentationwhich is essentially the conversion ofmalic acidintolactic acid.This has the benefit of reducing some of the tartness and making the resulting wine taste softer. Depending on the style of wine that the winemaker is trying to produce, malolactic fermentation may take place at the very same time as the yeast fermentation.[21]Alternatively, some strains of yeast may be developed that can convert L-malate to L-lactate during alcohol fermentation.[22]For example,Saccharomyces cerevisiaestrain ML01 (S. cerevisiae strainML01), which carries a gene encoding malolactic enzyme fromOenococcus oeniand a gene encoding malate permease fromSchizosaccharomyces pombe.S. cerevisiae strainML01 has received regulatory approval in both Canada and the United States.[23]

See also

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References

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  1. ^Jancis Robinson (ed):"The Oxford Companion to Wine"Third Edition, pp. 267–69. Oxford University Press 2006ISBN0198609906.
  2. ^Jancis Robinson:Jancis Robinson's Wine CourseThird Edition, pp. 74–84. Abbeville Press 2003ISBN0789208830.
  3. ^H. Johnson:Vintage: The Story of Winep. 16. Simon and Schuster 1989ISBN0671687026.
  4. ^J. Robinson (ed)"The Oxford Companion to Wine"Third Edition, p. 267. Oxford University Press 2006ISBN0198609906.
  5. ^Nigro, Dana. "Taking the Water out of Winemaking".Wine Spectator,2 October 2015.
  6. ^Cockcroft, Marlaina. "It's in the Bag".New Jersey Monthly,15 March 2017.
  7. ^Gemma Beltran, Maria Jesus Torija, Maite Novo, Noemi Ferrer, Montserrat Poblet, Jose M. Guillamon, Nicholas Rozes, and Albert Mas. “Analysis of Yeast Populations During Alcohol Fermentation: A Six Year Follow-up Study”. pp. 3–4Systematic and Applied Microbiology25.2 (2002): 287–93.
  8. ^Jancis Robinson (ed):"The Oxford Companion to Wine"Third Edition, pp. 778–79. Oxford University Press 2006ISBN0198609906.
  9. ^Gemma Beltran, Maria Jesus Torija, Maite Novo, Noemi Ferrer, Montserrat Poblet, Jose M. Guillamon, Nicholas Rozes, and Albert Mas. “Analysis of Yeast Populations During Alcohol Fermentation: A Six Year Follow-up Study”.Systematic and Applied Microbiology25. February 2002: 287–93.
  10. ^Jancis Robinson (ed):"The Oxford Companion to Wine",Third Edition p. 779. Oxford University Press 2006ISBN0198609906.
  11. ^abcJancis Robinson (ed):"The Oxford Companion to Wine",Third Edition p. 268. Oxford University Press 2006ISBN0198609906.
  12. ^"fermentation."Oddbins Dictionary of Wine.London: Bloomsbury Publishing Ltd, 2004. Credo Reference.
  13. ^J. Robinson (ed)The Oxford Companion to WineThird Edition, p. 780. Oxford University Press 2006ISBN0198609906.
  14. ^Jackson, Ronald S.Wine Science Principles and Applications,p. 277. San Diego, California: Academic Press, 2008.
  15. ^Jackson, Ronald S.;Wine Science Principles and Applications,p. 276. San Diego, California: Academic Press, 2008.[ISBN missing].
  16. ^Jancis Robinson:Jancis Robinson's Wine Course,Third Edition, p. 82. Abbeville Press 2003ISBN0789208830.
  17. ^Jackson, Ronald S.:Wine Science Principles and Applications,p. 276. San Diego, California: Academic Press, 2008[ISBN missing].
  18. ^K. MacNeil:The Wine Bible,pp. 168–69. Workman Publishing 2001ISBN1563054345.
  19. ^K. MacNeil:The Wine Bible,pp. 33–34. Workman Publishing 2001ISBN1563054345.
  20. ^D. Bird: "Understanding Wine Technology",pp. 89–92, DBQA Publishing 2005ISBN1891267914.
  21. ^K. MacNeil:The Wine Bible,p. 35. Workman Publishing 2001ISBN1563054345.
  22. ^"Wine Research Centre at UBC - Malolactic yeast ML01 – the Facts".Archived fromthe originalon 2012-03-16.Retrieved2012-03-05.
  23. ^"New substances: risk assessment summary EAU-224".Ec.gc.ca.October 2018.Retrieved17 November2018.
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