A column still called a continuous still, patent still or Coffey still, is a variety of still consisting of two columns. Sir Anthony Perrier was operator of the Spring Lane distillery in Cork, Ireland from 1806. In 1822 he patented one of Europe's first continuous whiskey stills, a method that during distillation allowed the wash to flow and continuously over the heat through a labyrinth of partitions; this meant small portions of fermented "wash" received the greatest amount of heat, thereby increasing the amount of potable alcohol, collected. In 1828, Perrier's invention inspired a Scotsman, Robert Stein, to create a still that fed the "wash" through a column of partitions, he called it a "patent still". It was first used at the Cameron Bridge Grain Distillery in Scotland. Despite numerous presentations in the British Isles and in Europe, he never got the financial support needed to get his project off the ground and into the distilleries. However, a demonstration of Stein's still observed by a Dublin excise tax collector, Aeneas Coffey, yielded the greatest result.
The design was to be patented by an Irishman, Aeneas Coffey. Educated at Dublin's Trinity College, Coffey had ample opportunities to observe all manner of still designs because he had worked for a quarter of a century as an excise tax collector, he knew. He knew that the new continuous stills had a flaw. To obtain a higher proof spirit, receiving vessels had to be changed so multiple distillations could take place. Coffey opened the Dock Distillery on Grand Canal Street in Dublin; the main feature of his operation was a customised still of his own design—or rather Stein’s design with a minor modification. Coffey inserted two pipes into Stein’s column still that allowed a greater portion of the vapours to re-circulate into the still instead of flowing into the receiver with the spirit; this eliminated the need for multi-distillation and produced a spirit with a higher proof and lighter character. In 1830, he was granted Patent a two-column continuous still. Nearly every liquor producer in Europe and the Americas embraced Coffey's new continuous column still.
Cuban rum, vodka, blended Scotch whisky, blended Irish whiskey all gained new stature as output went through the roof and the character of the spirit became smoother and more palatable. Within five years of receiving his patent, Coffey had enough orders to warrant the establishment of Aeneas Coffey & Sons in London, a company that remains in operation today under the name John Dore & Co Limited, he closed Dock Distillery four years and devoted all of his time to building and installing stills in distilleries owned by others. At the time, Irish distillers were the dominant force in global whiskey production. For Coffey, his invention was shunned by the Irish who considered the whiskey produced from his still as bland and tasteless, they decided to persevere with their famous pot still whiskey and Coffey was forced to look overseas and to Scotland in particular. The first column in a column still wash descending through several levels; the second column carries the alcohol from the wash, where it circulates until it can condense at the required strength.
Column stills behave like a series of single pot stills, formed in a long vertical tube. The tube is filled with bubble plates; the rising vapor, low in alcohol, starts to condense in the cooler, higher level of the column. The temperature of each successively higher stage is lower than the previous stage, so the vapor in equilibrium with the liquid at each stage is progressively more enriched with alcohol. Whereas a single pot still charged with wine might yield a vapor enriched to 40–50% alcohol, a column still can achieve a vapor alcohol content of 96%. Further enrichment is only possible by absorbing the remaining water using other means, such as hydrophilic chemicals or azeotropic distillation. A column still is an example of a fractional distillation, in that it yields a narrow fraction of the distillable components; this technique is employed in chemical synthesis. A continuous still can, sustain a constant process of distillation. This, along with the ability to produce a higher concentration of alcohol in the final distillate, is its main advantage over a pot still, which can only work in batches.
Continuous stills are charged with preheated feed liquor at some point in the column. Heat is supplied to the base of the column. Stripped liquid is drawn off at the base, while alcoholic spirits are condensed after migrating to the top of the column. Column stills are used in the production of grain whisky and are the most used type of still in the production of Bourbon and other American whiskeys. Distillation by column still is the traditional method for production of Armagnac, although distillation by pot still is allowed; the use of column stills for the distillation of Cognac is forbidden. Distillation by column stills are permitted for Calvados Domfrontais. Calvados Pays d'Auge AOC is required to be distilled by pot still. Pot still Batch distillation Coffey still
Brandy is a spirit produced by distilling wine. Brandy contains 35–60% alcohol by volume and is drunk as an after-dinner digestif; some brandies are aged in wooden casks. Others are coloured with caramel colouring to imitate the effect of aging, some are produced using a combination of both aging and colouring. Varieties of wine brandy can be found across the winemaking world. Among the most renowned are Cognac and Armagnac from southwestern France. In a broader sense, the term brandy denotes liquors obtained from the distillation of pomace, or mash or wine of any other fruit; these products are called eau de vie. The origins of brandy are tied to the development of distillation. While the process was known in classical times, it was not used for significant beverage production until the 15th century. Wine was distilled as a preservation method and as a way to make it easier for merchants to transport, it is thought that wine was distilled to lessen the tax, assessed by volume. The intent was to add the water removed by distillation back to the brandy shortly before consumption.
It was discovered that after having been stored in wooden casks, the resulting product had improved over the original distilled spirit. In addition to removing water, the distillation process led to the formation and decomposition of numerous aromatic compounds, fundamentally altering the composition of the distillate from its source. Non-volatile substances such as pigments and salts remained behind in the still; as a result, the taste of the distillate was quite unlike that of the original source. As described in the 1728 edition of Cyclopaedia, the following method was used to distill brandy: A cucurbit was filled half full of the liquor from which brandy was to be drawn and raised with a little fire until about one-sixth part was distilled, or until that which falls into the receiver was flammable; this liquor, distilled only once, was called spirit of brandy. Purified by another distillation, this was called spirit of wine rectified; the second distillation was made in balneo mariae and in a glass cucurbit, the liquor was distilled to about one half the quantity.
This was further rectified as long. To shorten these several distillations, which were long and troublesome, a chemical instrument was invented that reduced them to a single distillation. To test the purity of the rectified spirit of wine, a portion was ignited. If the entire contents were consumed by a fire without leaving any impurities behind the liquor was good. Another, better test involved putting a little gunpowder in the bottom of the spirit. If the gunpowder could ignite after the spirit was consumed by fire the liquor was good; as most brandies have been distilled from grapes, the regions of the world producing excellent brandies have paralleled those areas producing grapes for viniculture. At the end of the 19th century, the western European markets, including by extension their overseas empires, were dominated by French and Spanish brandies and eastern Europe was dominated by brandies from the Black Sea region, including Bulgaria, the Crimea, Georgia. In 1884, David Sarajishvili founded his brandy factory in Tbilisi, Georgia, a crossroads for Turkish, Central Asian, Persian trade routes and a part of the Russian Empire at the time.
Except for few major producers, brandy production and consumption tend to have a regional character and thus production methods vary. Wine brandy is produced from a variety of grape cultivars. A special selection of cultivars, providing distinct aroma and character, is used for high-quality brandies, while cheaper ones are made from whichever wine is available. Brandy is made from so-called base wine, which differs from regular table wines, it is made from early grapes in order to achieve lower sugar levels. Base wine contains smaller amount of sulphur than regular wines, as it creates undesired copper sulfate in reaction with copper in the pot stills; the yeast sediment produced during the fermentation may or may not be kept in the wine, depending on the brandy style. Brandy is distilled from the base wine in two phases. In the first, large part of water and solids is removed from the base, obtaining so-called "low wine" a concentrated wine with 28–30% ABV. In the second stage, low wine is distilled into brandy.
The liquid exits the pot still in three phases, referred to as the "heads", "heart" and "tails" respectively. The first part, the "head," has an alcohol concentration of an unpleasant odour; the weak portion on the end, "tail", is discarded along with the head, they are mixed with another batch of low wine, thereby entering the distillation cycle again. The middle heart fraction, richest in aromas and flavours, is preserved for maturation. Distillation does not enhance the alcohol content of wine; the heat under which the product is distilled and the material of the still cause chemical reactions to take place during distillation. This leads to the formation of numerous new volatile aroma components, changes in relative amounts of aroma components in the wine, the hydrolysis of components such as esters. Brandy is produced in pot stills, but the column still can be used for continuous distillation. Distillate obtained in this manner is less aromatic. Choice of the apparatus depends on the style of brandy produced.
Cognac and South Afric
Flavored fortified wine
Flavored fortified wines are inexpensive fortified wines that have an alcohol content between 13% and 20% alcohol by volume. They are made of grape and citrus wine and artificial flavor. Buckfast Tonic Wine is a caffeine- and sugar-laced tonic wine with added alcohol, produced under license from Buckfast Abbey, a Roman Catholic monastery located in Devon, England, it is popular in Glasgow, East Kilbride, Hamilton and other Strathclyde areas in Scotland, but critics have blamed it for being one cause of social problems in Scotland. Some have called it "Wreck the Hoose Juice". Cisco is the brand name of a fortified wine produced by the Centerra Wine Company with varieties selling at 13.9%, 17.5%, 19.5% alcohol by volume. Cisco has a syrupy sweet taste; the Federal Trade Commission required the company to put labels on their bottles stating that Cisco is not a wine cooler, to change the shape and color of their containers, to recall their advertising slogan "Takes you by surprise". MD 20/20 is an American fortified wine.
MD 20/20 has an alcohol content that varies by flavor from 13% to 18%. The MD stands for its producer: Mogen David. 20/20 stood for 20 oz at 20% alcohol. MD 20/20 is not sold in 20 oz bottles nor at 20% alcohol by volume. Richards Wild Irish Rose is an alcoholic beverage produced by Centerra Wine Company, part of the Constellation Brands organization, it was introduced in 1954 and sells about two million cases annually. The brand is available in 13.9% and 18% alcohol by volume. Solntsedar was a Soviet brand of low-end fortified wine, marketed as "port wine", infamous for many severe cases of poisoning, its production was canceled after Mikhail Gorbachev's anti-alcohol laws. Wild Russian Vanya was sold during the late 1960s and early 1970s, it was referred to in commercials as WILD RUSSIAN VANYA, WHAT A WINE. It was a fortified wine with about 20% alcohol by volume. Attempts were made to make people think it was a Russian import but it was not; this yellow peach-flavored wine was a favorite for some years among the street winos and tramps and a few college students.
It went out of production in the late 1970s, being outcompeted by Thunderbird, Night Train, Wild Irish Rose. Three popular brands in this category have been produced by the E & J Gallo Winery, were a large part of that company's early success. Ripple was a fortified wine produced by E & J Gallo Winery, popular in the United States in the 1970s. Possessing a low 11% ABV, it was marketed to "casual" drinkers. Due to its low price, it had a reputation as a drink for the destitute, it was popular among both underage and college students. It is no longer produced. Night Train Express abbreviated to Night Train contains 17.5% ABV. Night Train Express has been condemned by some civic leaders who think inexpensive high alcohol content drinks contribute to vagrancy and public drunkenness. Thunderbird, between 13% and 18% ABV. Popular since the 1950s, when a popular rhythm and blues song went: "What's the word? Thunderbird / How's it sold? Good and cold / What's the jive?'Bird's alive / What's the price? Thirty twice."
It was once marketed in the United Kingdom as "The California Aperitif". An early reference to the problem of cheap and poorly made wines is in the "Report on Cheap Wines" in the 5 November 1864 issue of The Medical Times and Gazette; the author, in prescribing inexpensive wines for a number of ills, cautions against the "fortified" wines of the day, describing of one sample that he had tried: When the cork was drawn it was scarcely tinted, was a bad one – a thing of no good augury for the wine. There was no smell of port wine; the liquid, when tasted, gave the palate half-a-dozen sensations instead of one. There was a hot taste of spirits, a sweet taste, a fruity taste like damsons, an unmistakable flavor of Roussillon, it was a strong, unwholesome liquor, purchased dearly. It is reported, that the popularity of cheap, fortified wines in the United States arose in the 1930s, as a product of Prohibition and the Great Depression: Prohibition produced the Roaring Twenties and fostered more beer and distilled-spirit drinkers than wine drinkers, because the raw materials were easier to come by.
But fortified wine, or medicinal wine tonic—containing about 20 percent alcohol, which made it more like a distilled spirit than regular wine—was still available and became America's number one wine. Thunderbird and Wild Irish Rose, to name two examples, are fortified wines. American wine was soon more popular for its effect than its taste. While overtaken somewhat in the low-end alcoholic drink market by sweetened malt beverages by the 1990s, the appeal of cheap fortified wines to the poor and homeless has raised concerns: Community groups in Los Angeles, San Francisco and Portland have urged makers of fortified wines such as Wild Irish Rose and E & J Gallo's Thunderbird and Night Train brands to pull their products from the shelves of liquor retailers in skid row areas. In Nashville, one liquor store owner told Nashville Business Jou
A sugar beet is a plant whose root contains a high concentration of sucrose and, grown commercially for sugar production. In plant breeding it is known as the Altissima cultivar group of the common beet. Together with other beet cultivars, such as beetroot and chard, it belongs to the subspecies Beta vulgaris subsp. Vulgaris, its closest wild relative is the sea beet. In 2013, France, the United States and Turkey were the world's five largest sugar beet producers. In 2010–2011, North America and Europe did not produce enough sugar from sugar beets to meet overall demand for sugar and were all net importers of sugar; the US harvested 1,004,600 acres of sugar beets in 2008. In 2009, sugar beets accounted for 20% of the world's sugar production; the sugar beet has a conical, fleshy root with a flat crown. The plant consists of a rosette of leaves. Sugar is formed by photosynthesis in the leaves and is stored in the root; the root of the beet contains 75% water, about 20% sugar, 5% pulp. The exact sugar content can vary between 12% and 21% sugar, depending on the cultivar and growing conditions.
Sugar is the primary value of sugar beet as a cash crop. The pulp, insoluble in water and composed of cellulose, hemicellulose and pectin, is used in animal feed; the byproducts of the sugar beet crop, such as pulp and molasses, add another 10% to the value of the harvest. Sugar beets grow in the temperate zone, in contrast to sugarcane, which grows in the tropical and subtropical zones; the average weight of sugar beet ranges between 1 kg. Sugar beet foliage grows to a height of about 35 cm; the leaves are numerous and broad and grow in a tuft from the crown of the beet, level with or just above the ground surface. Modern sugar beets date back to mid-18th century Silesia where the king of Prussia subsidised experiments aimed at processes for sugar extraction. In 1747, Andreas Marggraf isolated sugar from beetroots and found them at concentrations of 1.3–1.6%. He demonstrated that sugar could be extracted from beets, identical with sugar produced from sugarcane, his student, Franz Karl Achard, evaluated 23 varieties of mangelwurzel for sugar content and selected a local strain from Halberstadt in modern-day Saxony-Anhalt, Germany.
Moritz Baron von Koppy and his son further selected from this strain for conical tubers. The selection was named weiße schlesische Zuckerrübe, meaning white Silesian sugar beet, boasted about a 6% sugar content; this selection is the progenitor of all modern sugar beets. A royal decree led to the first factory devoted to sugar extraction from beetroots being opened in Kunern, Silesia in 1801; the Silesian sugar beet was soon introduced to France, where Napoleon opened schools for studying the plant. He ordered that 28,000 hectares be devoted to growing the new sugar beet; this was in response to British blockades of cane sugar during the Napoleonic Wars, which stimulated the rapid growth of a European sugar beet industry. By 1840, about 5% of the world's sugar was derived from sugar beets, by 1880, this number had risen more than tenfold to over 50%; the sugar beet was introduced to North America after 1830, with the first commercial production starting in 1879 at a farm in Alvarado, California.
The sugar beet was introduced to Chile by German settlers around 1850. "The beet-root, when being boiled, yields a juice similar to syrup of sugar, beautiful to look at on account of its vermilion color". This was written by 16th-century scientist, Olivier de Serres, who discovered a process for preparing sugar syrup from the common red beet. However, because crystallized cane sugar was available and provided a better taste, this process never caught on; this story characterizes the history of the sugar beet. The competition between beet sugar and sugarcane for control of the sugar market plays out from the first extraction of a sugar syrup from a garden beet into the modern day; the use of sugar beets for the extraction of crystallized sugar dates to 1747, when Andreas Sigismund Marggraf, professor of physics in the Academy of Science of Berlin, discovered the existence of a sugar in vegetables similar in its properties to that obtained from sugarcane. He found. Despite Marggraf’s success in isolating pure sugar from beets, their commercial manufacture for sugar did not take off until the early 19th century.
Marggraf's student and successor Franz Karl Achard began selectively breeding sugar beet from the'White Silesian' fodder beet in 1784. By the beginning of the 19th century, his beet was about 5–6% sucrose by weight, compared to around 20% in modern varieties. Under the patronage of Frederick William III of Prussia, he opened the world's first beet sugar factory in 1801, at Cunern in Silesia; the work of Achard soon attracted the attention of Napoleon Bonaparte, who appointed a commission of scientists to go to Silesia to investigate Achard's factory. Upon their return, two small factories were constructed near Paris. Although these factories were not altogether a success, the results attained interested Napoleon. Thus, when two events, the blockade of Europe by the British Navy and the Haitian Revolution, made the importation of cane sugar untenable, Napoleon seized the opportunity offered by beet sugar to address the shortage. In 1811, Napoleon issued a decree appropriating one million francs for the establishment of sugar schools, compelling the farmers to plant a large acreage to sugar be
Noble rot is the beneficial form of a grey fungus, Botrytis cinerea, affecting wine grapes. Infestation by Botrytis requires moist conditions. If the weather stays wet, the damaging form, "grey rot", can destroy crops of grapes. Grapes become infected with Botrytis when they are ripe. If they are exposed to drier conditions and become raisined this form of infection is known as noble rot. Grapes when picked at a certain point during infestation can produce fine and concentrated sweet wine. Wines produced by this method are known as botrytized wines. According to Hungarian legend, the first aszú was made by Laczkó Máté Szepsi in 1630. However, mention of wine made from botrytised grapes had appeared in the Nomenklatura of Fabricius Balázs Sziksai, completed in 1576. A discovered inventory of aszú predates this reference by five years; when vineyard classification began in 1730 in the Tokaj region, one of the gradings given to the various terroirs centered on their potential to develop Botrytis cinerea.
A popular myth is that the practice originated independently in Germany in 1775, where the Riesling producers at Schloss Johannisberg traditionally awaited the say-so of the estate owner, Heinrich von Bibra, Bishop of Fulda, before cutting their grapes. In this year, the abbey messenger was robbed en route to delivering the order to harvest and the cutting was delayed for three weeks, time enough for the Botrytis to take hold; the grapes were presumed worthless and given to local peasants, who produced a good, sweet wine which subsequently became known as Spätlese, or late harvest wine. In the following few years, several different classes of increasing must weight were introduced, the original Spätlese was further elaborated, first into Auslese in 1787 and Eiswein in 1858. In some cases, inoculation occurs when spores of the fungus are sprayed over the grapes, while some vineyards depend on natural inoculation from spores present in the environment; the fungus perforates the grapes' skin, allowing water in the grape to evaporate during dry conditions, thereby raising the sugar concentration in the remaining juice.
Some of the finest botrytized wines are picked berry by berry in successive tris. Internationally renowned botrytized wines include the aszú of Tokaj-Hegyalja in Hungary, Sauternes from France – where the process is known as pourriture or pourriture noble, Beerenauslese or Trockenbeerenauslese wines from Germany and Austria. Other wines of this type include the Romanian Grasă de Cotnari, French Coteaux du Layon, French Monbazillac, Austrian Ausbruch and South African Noble Late Harvest. Depending on conditions, the grapes may be only minimally botrytized. Botrytis has been imported for use by winemakers in California and Australia. University of California Pest Management Guidelines for Grape Botrytis Bunch Rot The Ohio State University Botrytis Bunch Rot Fact Sheet Botrytis Genome Sequencing Project, INRA, France
Madeira is a fortified wine made on the Portuguese Madeira Islands, off the coast of Africa. Madeira is produced in a variety of styles ranging from dry wines which can be consumed on their own as an aperitif to sweet wines consumed with dessert. Cheaper cooking versions are flavoured with salt and pepper for use in cooking, but these are not fit for consumption as a beverage; the islands of Madeira have a long winemaking history, dating back to the Age of Exploration when Madeira was a standard port of call for ships heading to the New World or East Indies. To prevent the wine from spoiling, neutral grape spirits were added. On the long sea voyages, the wines would be exposed to excessive heat and movement which transformed the flavour of the wine; this was discovered by the wine producers of Madeira when an unsold shipment of wine returned to the islands after a round trip. Today, Madeira is noted for its unique winemaking process which involves oxidizing the wine through heat and aging; the younger blends are produced with artificial methods that heat and accelerate the aging process and the older blends and frasqueiras are produced by the canteiro method.
Because of these methods of production these wines are long lived and those produced by the canteiro method will survive for decades and centuries after being opened. Wines that have been in barrels for many decades are removed and stored in demijohns where they may remain unharmed indefinitely; some wines produced in small quantities in Crimea and Texas are referred to as "Madeira" or "Madera". Most countries conform to the EU PDO regulations and limit the use of the term Madeira or Madère to only those wines that come from the Madeira Islands; the roots of Madeira's wine industry date back to the Age of Exploration, when Madeira was a regular port of call for ships travelling to the East Indies. By the 16th century, records indicate that a well-established wine industry on the island supplied these ships with wine for the long voyages across the sea; the earliest examples of Madeira had the habit of spoiling at sea. However, following the example of Port, a small amount of distilled alcohol made from cane sugar was added to stabilize the wine by boosting the alcohol content.
The Dutch East India Company became a regular customer, picking up large casks of wine known as "pipes" for their voyages to India. The intense heat in the holds of the ships had a transforming effect on the wine, as discovered by Madeira producers when one shipment was returned to the island after a long trip; the customer was found to prefer the taste of this style of wine, Madeira labeled as vinho da roda became popular. Madeira producers found that aging the wine on long sea voyages was costly, so began to develop methods on the island to produce the same aged and heated style, they began storing the wines on trestles at the winery or in special rooms known as estufas, where the heat of island sun would age the wine. The 18th century was the "golden age" for Madeira; the wine's popularity extended from the American colonies and Brazil in the New World to Great Britain and Northern Africa. The American colonies, in particular, were enthusiastic customers, consuming as much as 95% of all wine produced on the island each year.
Madeira was an important wine in the history of the United States of America. No wine-quality grapes were grown among the thirteen colonies, so imports were needed, with a great focus on Madeira. One of the major events on the road to the American revolution in which Madeira played a key role was the British seizure of John Hancock's sloop the Liberty on May 9, 1768. Hancock's boat was seized after he had unloaded a cargo of 25 pipes of Madeira, a dispute arose over import duties; the seizure of the Liberty caused riots to erupt among the people of Boston. Madeira was a favorite of Thomas Jefferson, it was used to toast the Declaration of Independence. George Washington, Alexander Hamilton, Benjamin Franklin and John Adams are said to have appreciated the qualities of Madeira; the wine was mentioned in Benjamin Franklin's autobiography. On one occasion, Adams wrote to his wife, Abigail, of the great quantities of Madeira he consumed while a Massachusetts delegate to the Continental Congress. A bottle of Madeira was used by visiting Captain James Server to christen the USS Constitution in 1797.
Chief Justice John Marshall was known to appreciate Madeira, as were his cohorts on the early U. S. Supreme Court; the mid-19th century ushered an end to the industry's prosperity. First came the 1851 discovery of powdery mildew, which reduced production over the next three years. Just as the industry was recovering through the use of the copper-based Bordeaux mixture fungicide, the phylloxera epidemic that had plagued France and other European wine regions reached the island. By the end of the 19th century, most of the island's vineyards had been uprooted, many were converted to sugar cane production; the majority of the vineyards that did replant chose to use American vine varieties, such as Vitis labrusca, Vitis riparia and Vitis rupestris or hybrid grape varieties rather than replant with the Vitis vinifera varieties that were grown. By the turn of the 20th century, sales started to return to normal, until the industry was rocked again by the Russian Civil War and American Prohibition, which closed off two of Madeira's biggest markets.
After the repeal of Prohibition, during a time in which shipping technology had improved, the ships no longer needed to
Yeast in winemaking
The role of yeast in winemaking is the most important element that distinguishes wine from grape juice. In the absence of oxygen, yeast converts the sugars of wine grapes into alcohol and carbon dioxide through the process of fermentation; the more sugars in the grapes, the higher the potential alcohol level of the wine if the yeast are allowed to carry out fermentation to dryness. Sometimes winemakers will stop fermentation early in order to leave some residual sugars and sweetness in the wine such as with dessert wines; this can be achieved by dropping fermentation temperatures to the point where the yeast are inactive, sterile filtering the wine to remove the yeast or fortification with brandy or neutral spirits to kill off the yeast cells. If fermentation is unintentionally stopped, such as when the yeasts become exhausted of available nutrients and the wine has not yet reached dryness, this is considered a stuck fermentation; the most common yeast associated with winemaking is Saccharomyces cerevisiae, favored due to its predictable and vigorous fermentation capabilities, tolerance of high levels of alcohol and sulfur dioxide as well as its ability to thrive in normal wine pH between 2.8 and 4.
Despite its widespread use which includes deliberate inoculation from cultured stock, S. cerevisiae is the only yeast species involved in a fermentation. Grapes brought in from harvest are teeming with a variety of "wild yeast" from the Kloeckera and Candida genera; these yeasts begin the fermentation process as soon as the grapes are picked when the weight of the clusters in the harvest bins begin to crush the grapes, releasing the sugar-rich must. While additions of sulfur dioxide may limit some of the wild yeast activities, these yeasts will die out once the alcohol level reaches about 15% due to the toxicity of alcohol on the yeast cells physiology while the more alcohol tolerant Saccharomyces species take over. In addition to S. cerevisiae, Saccharomyces bayanus is a species of yeast that can tolerate alcohol levels of 17–20% and is used in fortified wine production such as ports and varieties such as Zinfandel and Syrah harvested at high Brix sugar levels. Another common yeast involved in wine production is Brettanomyces whose presence in a wine may be viewed by different winemakers as either a wine fault or in limited quantities as an added note of complexity.
For most of the history of wine, winemakers did not know the mechanism that somehow converted sugary grape juice into alcoholic wine. They could observe the fermentation process, described as "boiling", "seething" or the wine being "troubled" due to release of carbon dioxide that gave the wine a frothy, bubbling appearance; this history is preserved in the etymology of the word "yeast" itself which means "to boil". In the mid-19th century, the French scientist Louis Pasteur was tasked by the French government to study what made some wines spoil, his work, which would lead to Pasteur being considered one of the "Fathers of Microbiology", would uncover the connection between microscopic yeast cells and the process of the fermentation. It was Pasteur who discovered that yeast converted sugars in the must into alcohol and carbon dioxide, though the exact mechanisms of how the yeast would accomplish this task was not discovered till the 20th century with the Embden–Meyerhof–Parnas pathway; the yeast species known as Saccharomyces cerevisiae was first identified in late 19th century enology text as Saccharomyces ellipsoideus due to the elliptical shape of the cells.
Throughout the 20th century, more than 700 different strains of Saccharomyces cerevisiae were identified. The difference between the vast majority of these strains are minor, though individual winemakers will develop a preference for particular strains when making certain wines or working with particular grape varieties; some of these difference include the "vigor" or speed of fermentation, temperature tolerance, the production of volatile sulfur compounds and other compounds that may influence the aroma of the wine. The primary role of yeast is to convert the sugars present in the grape; the yeast accomplishes this by utilizing glucose through a series of metabolic pathways that, in the presence of oxygen, produces not only large amounts of energy for the cell but many different intermediates that the cell needs to function. In the absence of oxygen, the cell will continue some metabolic functions but will rely on other pathways such as reduction of acetaldehyde into ethanol to "recharge" the co-enzymes needed to keep metabolism going.
It is through this process of fermentation that ethanol is released by the yeast cells as a waste product. If the yeast cells are healthy and fermentation is allowed to run to the completion, all fermentable sugars will be used up by the yeast with only the unfermentable pentose leaving behind a negligible amount of residual sugar. While the production of alcohol is the most noteworthy by-product of yeast metabolism from a winemaking perspective, there are a number of other products that yeast produce that can be influence the resulting wine; this includes glycerol, produced when an intermediate of the glycolysis cycle is reduced to "recharge" the NADH enzyme needed to continue other metabolic activities. This is produced early in the fermentation process before the mechanisms to reduce acetaldehyde into ethanol to recharge NADH becomes the cell's primary means of maintaining redox balance; as glycerol contributes increased body and a sweet taste without increasing