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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.
Malolactic conversion is a process in winemaking in which tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid. Malolactic fermentation is most often performed as a secondary fermentation shortly after the end of the primary fermentation, but can sometimes run concurrently with it. The process is standard for most red wine production and common for some white grape varieties such as Chardonnay, where it can impart a "buttery" flavor from diacetyl, a byproduct of the reaction.
Ethanol fermentation, also called alcoholic fermentation, is a biological process which converts sugars such as glucose, fructose, and sucrose into cellular energy, producing ethanol and carbon dioxide as by-products. Because yeasts perform this conversion in the absence of oxygen, alcoholic fermentation is considered an anaerobic process. It also takes place in some species of fish where it provides energy when oxygen is scarce.
Ethyl acetate is the organic compound with the formula CH3CO2CH2CH3, simplified to C4H8O2. This colorless liquid has a characteristic sweet smell and is used in glues, nail polish removers, and the decaffeination process of tea and coffee. Ethyl acetate is the ester of ethanol and acetic acid; it is manufactured on a large scale for use as a solvent.
A wine fault is a sensory-associated (organoleptic) characteristic of a wine that is unpleasant, and may include elements of taste, smell, or appearance, elements that may arise from a "chemical or a microbial origin", where particular sensory experiences might arise from more than one wine fault. Wine faults may result from poor winemaking practices or storage conditions that lead to wine spoilage.
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.
Fermentation is a type of redox metabolism carried out in the absence of oxygen. During fermentation, organic molecules are catabolized and donate electrons to other organic molecules. In the process, ATP and organic end products are formed.
Pichia is a genus of yeasts in the family Pichiaceae with spherical, elliptical, or oblong acuminate cells. Pichia is a teleomorph, and forms hat-shaped, hemispherical, or round ascospores during sexual reproduction. The anamorphs of some Pichia species are Candida species. The asexual reproduction is by multilateral budding.
The Pasteur effect describes how available oxygen inhibits ethanol fermentation, driving yeast to switch toward aerobic respiration for increased generation of the energy carrier adenosine triphosphate (ATP). More generally, in the medical literature, the Pasteur effect refers to how the cellular presence of oxygen causes in cells a decrease in the rate of glycolysis and also a suppression of lactate accumulation. The effect occurs in animal tissues, as well as in microorganisms belonging to the fungal kingdom.
Acetyl-CoA synthetase (ACS) or Acetate—CoA ligase is an enzyme involved in metabolism of acetate. It is in the ligase class of enzymes, meaning that it catalyzes the formation of a new chemical bond between two large molecules.
Ann C. Noble is a sensory chemist and retired professor from the University of California, Davis. During her time at the UC Davis Department of Viticulture and Enology, Noble invented the "Aroma Wheel" which is credited with enhancing the public understanding of wine tasting and terminology. At the time of her hiring at UC Davis in 1974, Noble was the first woman hired as a faculty member of the Viticulture department. Noble retired from Davis in 2002 and in 2003 was named Emeritus Professor of Enology. Since retirement she has participated as a judge in the San Francisco Chronicle Wine Competition.
Ethyl gallate is a food additive with E number E313. It is the ethyl ester of gallic acid. Ethyl gallate is added to food as an antioxidant.
Brettanomyces claussenii is a wild yeast of the genus Brettanomyces which has a negative Pasteur effect. It and Brettanomyces anomalus share identical mtDNA. In the wild, it is found on the skins of fruit. It has been shown to be useful for wine and beer fermentation as well as ethanol production.
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.
Acetobacter aceti, a Gram-negative bacterium that moves using its peritrichous flagella, was discovered when Louis Pasteur proved it to be the cause of conversion of ethanol to acetic acid in 1864. Today, A.aceti is recognized as a species within the genus Acetobacter, belonging to the family Acetobacteraceae in the class Alphaproteobacteria. Its bacterial motility plays an important role in the formation of biofilms, intricate communities where A. aceti cells aggregate and collaborate, further enhancing their ability to metabolize ethanol and produce acetic acid. Widely distributed in various environmental niches, this benign microorganism thrives in habitats abundant in fermentable sugars, such as flowers, fruits, honey, water, and soil, present wherever sugar fermentation occurs. A. aceti grows best within temperatures ranging from 25 to 30 degrees Celsius, with an upper limit of 35 degrees Celsius, and in slightly acidic conditions with a pH between 5.5 to 6.3. A. aceti has long been used in the fermentation industry efficiently producing acetic acid from alcohol as an obligate aerobe dependent on oxygen as the terminal electron acceptor. A. aceti, classified as an acidophile, able to survive in acidic environments, possesses an acidified cytoplasm, providing most proteins with acid stability. The microorganism's ability to thrive in environments rich in fermentable sugars shows its potential as an organism for studying microbial metabolism and adaptation.
Aerobic fermentation or aerobic glycolysis is a metabolic process by which cells metabolize sugars via fermentation in the presence of oxygen and occurs through the repression of normal respiratory metabolism. Preference of aerobic fermentation over aerobic respiration is referred to as the Crabtree effect in yeast, and is part of the Warburg effect in tumor cells. While aerobic fermentation does not produce adenosine triphosphate (ATP) in high yield, it allows proliferating cells to convert nutrients such as glucose and glutamine more efficiently into biomass by avoiding unnecessary catabolic oxidation of such nutrients into carbon dioxide, preserving carbon-carbon bonds and promoting anabolism.
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.
The Wickerhamomycetaceae are a family of yeasts in the order Saccharomycetales that reproduce by budding. Species in the family have a widespread distribution.
Wickerhamomyces is a genus of fungi within the Saccharomycetales order. It is placed within the family of Phaffomycetaceae.
Cyberlindnera is a genus of yeasts in the Phaffomycetaceae family. Its name is derived from the Latin word “Ciber,” which originates from “Cibus,” meaning “food” and "sustenance". Early German mycologist Paul Lindner, honored for his contributions to descriptions of Schizosaccharomyces pombe, Saccharomycopsis (Endomyces) fibuligera and other notable species of Saccharomyces and Pichia, is the source of the "-lindnera" portion of the name. The genus has gone through many trials, reevaluations, and verifications to become the organized assortment of species it is today. Species under this genus interact with other organisms in a wide variety of ways and can be found across the globe. They are used by humans for their toxicity, fermentation abilities, and capacity to assimilate many organic compounds.
References
- ↑ Kurtzman, Cletus P. (2011). "Phylogeny of the ascomycetous yeasts and the renaming of Pichia anomala to Wickerhamomyces anomalus". Antonie van Leeuwenhoek. 99: 13–23. doi:10.1007/s10482-010-9505-6.
- 1 2 3 "Pichia anomala | Viticulture & Enology". wineserver.ucdavis.edu. Retrieved 2016-04-16.
- ↑ "Oxygen- and Glucose-Dependent Regulation of Central Carbon Metabolism in Pichia anomala". aem.asm.org. Retrieved 2016-04-16.
- ↑ Madrigal, T.; Maicas, S.; Mateo Tolosa, J. J. (2013-03-01). "Glucose and Ethanol Tolerant Enzymes Produced by Pichia (Wickerhamomyces) Isolates from Enological Ecosystems". American Journal of Enology and Viticulture. 64 (1): 126–133. doi:10.5344/ajev.2012.12077. ISSN 0002-9254. S2CID 86753667.
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