Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitute 1% of all described fungal species.
Baker's yeast is the common name for the strains of yeast commonly used in baking bread and other bakery products, serving as a leavening agent which causes the bread to rise by converting the fermentable sugars present in the dough into carbon dioxide and ethanol. Baker's yeast is of the species Saccharomyces cerevisiae, and is the same species as the kind commonly used in alcoholic fermentation, which is called brewer's yeast or the deactivated form nutritional yeast. Baker's yeast is also a single-cell microorganism found on and around the human body.
Kilju is the Finnish word for home made alcoholic beverage typically made of sugar, yeast, and water.
Saccharomyces is a genus of fungi that includes many species of yeasts. Saccharomyces is from Greek σάκχαρον (sugar) and μύκης (fungus) and means sugar fungus. Many members of this genus are considered very important in food production where they are known as brewer's yeast, baker's yeast and sourdough starter among others. They are unicellular and saprotrophic fungi. One example is Saccharomyces cerevisiae, which is used in making bread, wine, and beer, and for human and animal health. Other members of this genus include the wild yeast Saccharomyces paradoxus that is the closest relative to S. cerevisiae, Saccharomyces bayanus, used in making wine, and Saccharomyces cerevisiaevar. boulardii, used in medicine.
Torulaspora delbrueckii is a ubiquitous yeast species with both wild and anthropic habitats. The type strain of T. delbrueckii is CBS 1146T, equivalent to CLIB 230 or ATCC 10662, etc.. The type strain of T. delbrueckii CBS 1146 T was sequenced in 2009, and is composed of 8 chromosomes in addition to a mitochondrial genome.
Zygosaccharomyces bailii is a species in the genus Zygosaccharomyces. It was initially described as Saccharomyces bailii by Lindner in 1895, but in 1983 it was reclassified as Zygosaccharomyces bailii in the work by Barnett et al.
Candida stellata is a species of yeast of the genus Candida. The year of 1978 saw work of Yarrow & Meyer the yeast was reclassified to its current name from Saccharomyces stellatus, which was initially described by Kroemer and Krumbholz in 1931.
The Crabtree effect, named after the English biochemist Herbert Grace Crabtree, describes the phenomenon whereby the yeast, Saccharomyces cerevisiae, produces ethanol (alcohol) in aerobic conditions at high external glucose concentrations rather than producing biomass via the tricarboxylic acid (TCA) cycle, the usual process occurring aerobically in most yeasts e.g. Kluyveromyces spp. This phenomenon is observed in most species of the Saccharomyces, Schizosaccharomyces, Debaryomyces, Brettanomyces, Torulopsis, Nematospora, and Nadsonia genera. Increasing concentrations of glucose accelerates glycolysis which results in the production of appreciable amounts of ATP through substrate-level phosphorylation. This reduces the need of oxidative phosphorylation done by the TCA cycle via the electron transport chain and therefore decreases oxygen consumption. The phenomenon is believed to have evolved as a competition mechanism around the time when the first fruits on Earth fell from the trees. The Crabtree effect works by repressing respiration by the fermentation pathway, dependent on the substrate.
Symbiotic culture of bacteria and yeast (SCOBY) is a culinary symbiotic fermentation culture (starter) consisting of lactic acid bacteria (LAB), acetic acid bacteria (AAB), and yeast which arises in the preparation of sour foods and beverages such as kombucha. Beer and wine also undergo fermentation with yeast, but the lactic acid bacteria and acetic acid bacteria components unique to SCOBY are usually viewed as a source of spoilage rather than a desired addition. Both LAB and AAB enter on the surface of barley and malt in beer fermentation and grapes in wine fermentation; LAB lowers the pH of the beer/wine while AAB takes the ethanol produced from the yeast and oxidizes it further into vinegar, resulting in a sour taste and smell. AAB are also responsible for the formation of the cellulose SCOBY.
D-Xylose is a five-carbon aldose that can be catabolized or metabolized into useful products by a variety of organisms.
The process of fermentation in winemaking turns grape juice into an alcoholic beverage. During fermentation, yeasts transform sugars present in the juice into ethanol and carbon dioxide. In winemaking, the temperature and speed of fermentation are important considerations as well as the levels of oxygen present in the must at the start of the fermentation. The risk of stuck fermentation and the development of several wine faults can also occur during this stage, which can last anywhere from 5 to 14 days for primary fermentation and potentially another 5 to 10 days for a secondary fermentation. Fermentation may be done in stainless steel tanks, which is common with many white wines like Riesling, in an open wooden vat, inside a wine barrel and inside the wine bottle itself as in the production of many sparkling wines.
A killer yeast is a yeast, such as Saccharomyces cerevisiae, which is able to secrete one of a number of toxic proteins which are lethal to susceptible cells. These "killer toxins" are polypeptides that kill sensitive cells of the same or related species, often functioning by creating pores in target cell membranes. These yeast cells are immune to the toxic effects of the protein due to an intrinsic immunity. Killer yeast strains can be a problem in commercial processing because they can kill desirable strains. The killer yeast system was first described in 1963. Study of killer toxins helped to better understand the secretion pathway of yeast, which is similar to those of more complex eukaryotes. It also can be used in treatment of some diseases, mainly those caused by fungi.
Cider is an alcoholic beverage made from the fermented juice of apples. Cider is widely available in the United Kingdom and Ireland. The UK has the world's highest per capita consumption, as well as the largest cider-producing companies. Ciders from the South West of England are generally higher in alcoholic content. Cider is also popular in many Commonwealth countries, such as India, South Africa, Canada, Australia, and New Zealand. As well as the UK and its former colonies, cider is popular in Portugal, France, Friuli, and northern Spain. Germany also has its own types of cider with Rhineland-Palatinate and Hesse producing a particularly tart version known as Apfelwein. In the U.S. and Canada, varieties of alcoholic cider are often called hard cider to distinguish it from non-alcoholic apple cider or "sweet cider", also made from apples. In Canada, cider cannot contain less than 2.5% or over 13% absolute alcohol by volume.
The role of yeast in winemaking is the most important element that distinguishes wine from fruit juice. In the absence of oxygen, yeast converts the sugars of the fruit 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.
Metschnikowia pulcherrima is a ubiquitous species of yeast, with numerous strains, belonging to the family Metschnikowiaceae, and found on grapes, cherries, flowers, spoiled fruit and consequently carried by fruit flies. It is a non-Saccharomyces yeast and plays an important role in the vinification of wine when it is present on grapes or winery equipment, and has historically seen use in South Africa’s wine industry. It is also being studied at the University of Bath as a possible alternative to the use of Palm oil, and early results show promise. M. pulcherrima is ovoid to ellipsoidal in shape and reproduces by budding. Its cells are globose and thick-walled, holding a single, large oil droplet of high refractive index. As the result of incomplete budding where cells remain attached after division, pseudohyphae may form under anaerobic conditions.
Saccharomycodes is a genus of yeasts. They are helobiallly reproducing yeasts. The type species is Saccharomycodes ludwigii. The other species, Saccharomycodes sinensis, is known from a single strain that was isolated from soil from a forest on Mount Chienfang on Hainan in China. It is the sister genus of Hanseniaspora.
Marie Antoine Alexandre Guilliermond was a French botanist and mycologist who specialized in cytological studies of the yeasts, fungi, and algae. He was among the first to identify sexual reproduction in yeast and published a major review on the yeasts in 1912.
Hanseniaspora gamundiae is a species of yeast in the family Saccharomycodaceae. It has been isolated from the fruiting bodies of Cyttaria hariotii mushrooms in Patagonia and is likely responsible for the early stages of fermentation of an alcoholic chicha produced from the mushrooms.
Hanseniaspora osmophila is a species of yeast in the family Saccharomycetaceae. It is found in soil and among the bark, leaves, and fruits of plants, as well as fermented foods and beverages made from fruit.
Zygosaccharomyces rouxii is a species of yeast in the genus Zygosaccharomyces. Initially described as Saccharomyces rouxii by Boutroux in 1883, it was then moved to the genus Zygosaccharomyces in the work of Barnett et al. It is remarkably tolerant of high concentrations of sugar or salt, making it a spoilage agent of otherwise stable foods, but also present in fermentation of products such as soy sauce or balsamic vinegar.
