fermentation temperature of the beverage fluctuates during the process. lager yeast normally ferments at a temperature of approximately 5 °c (41 °f), where saccharomyces cerevisiae becomes dormant. a variant yeast known as saccharomyces cerevisiae var. diastaticus is a beer spoiler which can cause secondary fermentations in packaged products. in may 2013, the oregon legislature made s. cerevisiae the official state microbe in recognition of the impact craft beer brewing has had on the state economy and the state's identity. baking s. cerevisiae is used in baking; the carbon dioxide generated by the fermentation is used as a leavening agent in bread and other baked goods. historically, this use was closely linked to the brewing industry's use of yeast, as bakers took or bought the barm or yeast-filled foam from brewing ale from the brewers (producing the barm cake); today, brewing and baking yeast strains are somewhat different. nutritional yeast saccharomyces cerevisiae is the main source of nutritional yeast, which is sold commercially as a food product. it is popular with vegans and vegetarians as an ingredient in cheese substitutes, or as a general food additive as a source of vitamins and minerals, especially amino acids and b-complex vitamins. uses in aquaria owing to the high cost of commercial co2 cylinder systems, co2 injection by yeast is one of the most popular diy approaches followed by aquaculturists for providing co2 to underwater aquatic plants. the yeast culture is, in general, maintained in plastic bottles, and typical systems provide one bubble every 3–7 seconds. various approaches have been devised to allow proper absorption of the gas into the water. direct use in medicine saccharomyces cerevisiae is used as a probiotic in humans and animals. the strain saccharomyces cerevisiae var. boulardii is industrially manufactured and used clinically as a medication. several clinical and experimental studies have shown that s. cerevisiae var. boulardii is, to lesser or greater extent, useful for prevention or treatment of several gastrointestinal diseases. moderate quality evidence has shown s. cerevisiae var. boulardii reduces risk of antibiotic-associated diarrhoea both in adults and in children and to reduce risk of adverse effects of helicobacter pylori eradication therapy. there is some evidence to support efficacy of s. cerevisiae var. boulardii in prevention (but not treatment) of traveler's diarrhoea and, at least as an adjunct medication, in treatment of acute diarrhoea in adults and children and of persistent diarrhoea in children. it may also reduce symptoms of allergic rhinitis. administration of s. cerevisiae var. boulardii is considered generally safe. in clinical trials it was well tolerated by patients, and adverse effects rate was similar to that in control groups (i. e. groups with placebo or no treatment). no case of s. cerevisiae var. boulardii fungemia has been reported during clinical trials. in clinical practice, however, cases of fungemia, caused by s. cerevisiae var. boulardii are reported. patients with compromised immunity or those with central vascular catheters are at special risk. some researchers have recommended avoiding use of s. cerevisiae var. boulardii as treatment in such patients. others suggest only that caution must be exercised with its use in risk group patients. a human pathogen saccharomyces cerevisiae is proven to be an opportunistic human pathogen, though of relatively low virulence. despite widespread use of this microorganism at home and in industry, contact with it very rarely leads to infection. saccharomyces cerevisiae was found in the skin, oral cavity, oropharinx, duodenal mucosa, digestive tract, and vagina of healthy humans (one review found it to be reported for 6% of samples from human intestine). some specialists consider s. cerevisiae to be a part of the normal microbiota of the gastrointestinal tract, the respiratory tract, and the vagina of humans, while others believe that the species cannot be called a true commensal because it originates in food. presence of s. cerevisiae in the human digestive system may be rather transient; for example, experiments show that in the case of oral administration to healthy individuals it is eliminated from the intestine within 5 days after the end of administration. under certain circumstances, such as degraded immunity, saccharomyces cerevisiae can cause infection in humans. studies show that it causes 0.45–1.06% of the cases of yeast-induced vaginitis. in some cases, women suffering from s. cerevisiae-induced vaginal infection were intimate partners of bakers, and the strain was found to be the same that their partners used for baking. as of 1999, no cases of s. cerevisiae-induced vaginitis in women, who worked in bakeries themselves, were reported in scientific literature. some cases were linked by researchers to the use of the yeast in home baking. cases of infection of oral cavity and pharynx caused by s. cerevisiae are also known. invasive and systemic infections occasionally saccharomyces cerevisiae causes invasive infections (i. e. gets into the bloodstream or other normally sterile body fluid or into a deep site tissue, such as lungs, liver or spleen) that can go systemic (involve multiple organs). such conditions are life-threatening. more than 30% cases of s. cerevisiae invasive infections lead to death even if treated. s. cerevisiae invasive infections, however, are much rarer than invasive infections caused by candida albicans even in patients weakened by cancer. s. cerevisiae causes 1% to 3.6% nosocomial cases of fungemia. a comprehensive review of s. cerevisiae invasive infection cases found all patients to have at least one predisposing condition. saccharomyces cerevisiae may enter the bloodstream or get to other deep sites of the body by translocation from oral or enteral mucosa or through contamination of intravascular catheters (e. g. central venous catheters). intravascular catheters, antibiotic therapy and compromised immunity are major predisposing factors for s. cerevisiae invasive infection. a number of cases of fungemia were caused by intentional ingestion of living s. cerevisiae cultures for dietary or therapeutic reasons, including use of saccharomyces boulardii (a strain of s. cerevisiae which is used as a probiotic for treatment of certain forms of diarrhea). saccharomyces boulardii causes about 40% cases of invasive saccharomyces infections and is more likely (in comparison to other s. cerevisiae strains) to cause invasive infection in humans without general problems with immunity, though such adverse effect is very rare relative to saccharomyces boulardii therapeutic administration. s. boulardii may contaminate intravascular catheters through hands of medical personnel involved in administering probiotic preparations of s. boulardii to patients. systemic infection usually occurs in patients who have their immunity compromised due to severe illness (hiv/aids, leukemia, other forms of cancer) or certain medical procedures (bone marrow transplantation, abdominal surgery). a case was reported when a nodule was surgically excised from a lung of a man employed in baking business, and examination of the tissue revealed presence of saccharomyces cerevisiae. inhalation of dry baking yeast powder is supposed to be the source of infection in this case. virulence of different strains statue of saccharomyces cerevisiae (hustopeče, czech republic) not all strains of saccharomyces cerevisiae are equally virulent towards humans. most environmental strains are not capable of growing at temperatures above 35 °c (i. e. at temperatures of living body of humans and other mammalian). virulent strains, however, are capable of growing at least above 37 °c and often up to 39 °c (rarely up to 42 °c). some industrial strains are also capable of growing above 37 °c. european food safety authority (as of 2017) requires that all s. cerevisiae strains capable of growth above 37 °c that are added to the food or feed chain in viable form must, as to be qualified presumably safe, show no resistance to antimycotic drugs used for treatment of yeast infections. the ability to grow at elevated temperatures is an important factor for strain's virulence but not the sole one. other traits that are usually believed to be associated with virulence are: ability to produce certain enzymes such as proteinase and phospholipase, invasive growth (i.e. growth with intrusion into the nutrient medium), ability to adhere to mammalian cells, ability to survive in the presence of hydrogen peroxide (that is used by macrophages to kill foreign microorganisms in the body) and other abilities allowing the yeast to resist or influence immune response of the host body. ability to form branching chains of cells, known as pseudohyphae is also sometimes said to be associated with virulence, though some research suggests that this trait may be common to both virulent and non-virulent strains of saccharomyces cerevisiae.