Question: Are yeasts able to grown food with low PH?
About the article "Yeast", section "Food spoilage".

Candidate passages:
Yeasts are able to grow in foods with a low pH (5.0 or lower) and in the presence of sugars, organic acids, and other easily metabolized carbon sources.
During their growth, yeasts metabolize some food components and produce metabolic end products.
This causes the physical, chemical, and sensible properties of a food to change, and the food is spoiled.
The growth of yeast within food products is often seen on their surfaces, as in cheeses or meats, or by the fermentation of sugars in beverages, such as juices, and semiliquid products, such as syrups and jams.
The yeast of the "Zygosaccharomyces" genus have had a long history as spoilage yeasts within the food industry.
This is mainly because these species can grow in the presence of high sucrose,ethanol, acetic acid, sorbic acid, benzoic acid, and sulphur dioxide concentrations, representing some of the commonly used food preservation methods.
Methylene blue is used to test for the presence of live yeast cells.
In oenology, the major spoilage yeast is "Dekkera bruxellensis ".
An outstanding feature of "Z. bailii" is its exceptional resistance to weak acid preservatives commonly used in foods and beverages, such as acetic, lactic, propionic, benzoic, sorbic acids and sulfur dioxide.
In addition, it is reported that the yeast is able to tolerate high ethanol concentrations (≥ 15% (v/v)).
The ranges of pH and aw for growth are wide, 2.0 - 7.0 and 0.80 - 0.99, respectively.
Besides being preservative resistant, other features that contribute to the spoilage capacity of "Z. bailii" are: (i) its ability to vigorously ferment hexose sugars (e.g.
glucose and fructose), (ii) ability to cause spoilage from an extremely low inoculum (e.g.
one viable cell per package of any size), (iii) moderate osmotolerance (in comparison to "Zygosaccharomyces rouxii").
Therefore, foods at particular risk to spoilage by this yeast usually have low pH (2.5 to 5.0), low aw and contain sufficient amounts of fermentable sugars.
The extreme acid resistance of "Z. bailii" has been reported by many authors.
On several occasions, growth of the yeast has been observed in fruit-based alcohols (pH 2.8 - 3.0, 40 - 45% (w/v) sucrose) preserved with 0.08% (w/v) benzoic acid, and in beverages (pH 3.2) containing either 0.06% (w/v) sorbic acid, 0.07% (w/v) benzoic acid, or 2% (w/v) acetic acid.
Notably, individual cells in any "Z. bailii" population differ considerably in their resistance to sorbic acid, with a small fraction able to grow in preservative levels double that of the average population.
In some types of food, the yeast is even able to grow in the presence of benzoic and sorbic acids at concentrations higher than those legally permitted and at pH values below the pKa of the acids.
For example, according to the European Union (EU) legislation, sorbic acid is limited to 0.03% (w/v) in soft drinks (pH 2.5 - 3.2); however "Z. bailii" can grow in soft drinks containing 0.05% (w/v) of this acid (pKa 4.8).
Particularly, there is strong evidence that the resistance of "Z. bailii" is stimulated by the presence of multiple preservatives.
Hence, the yeast can survive and defeat synergistic preservative combinations that normally provide microbiological stability to processed foods.
It has been observed that the cellular acetic acid uptake was inhibited when sorbic or benzoic acid was incorporated into the culture medium.
Similarly, ethanol levels up to 10% (v/v) did not adversely influence sorbic and benzoic acid resistance of the yeast at pH 4.0 - 5.0.
Moreover, Sousa et al.
(1996) have proved that in "Z. bailii", ethanol plays a protective role against the negative effect of acetic acid by inhibiting the transport and accumulation of this acid intracellularly.
Like other microorganisms, "Z. bailii" has the ability to adapt to sub-inhibitory levels of a preservative, which enables the yeast to survive and grow in much higher concentrations of the preservative than before adaptation.
In addition, it seems that "Z. bailii" resistance to acetic, benzoic and propionic acid is strongly correlated, as the cells which were adapted to benzoic acid also showed enhanced tolerances to other the preservatives.
Some studies have revealed the negligible effects of different sugars on preservative resistance of "Z. bailii", e.g.
comparable sorbic and benzoic acid resistance was observed regardless whether the cells were grown in culture medium containing glucose or fructose as fermentable substrates.
However, the preservative resistance of the yeast is influenced by glucose level, with maximum resistance obtained at 10 - 20% (w/v) sugar concentrations.
As "Z. bailii" is moderately osmotolerant, the salt and sugar levels in foods are usually insufficient to control its growth.
The highest tolerance to salt has been observed at low pH values, e.g.
the maximum NaCl allowing growth was 12.5% (w/v) at pH 3.0 whereas this was only 5.0% (w/v) at pH 5.0.
Moreover, the presence of either salt or sugar has a positive effect on the ability of "Z. bailii" to initiate growth at extreme pH levels, e.g.
the yeast showed no growth at pH 2.0 in the absence of NaCl and sucrose, but grew at this pH in 2.5% (w/v) NaCl or 50% (w/v) sucrose.
Most facultatively fermentative yeast species cannot grow in the complete absence of oxygen.
That means limitation of oxygen availability might be useful in controlling food spoilage caused by fermentative yeasts.
However, it has been observed that "Z. bailii" is able to grow rapidly and ferment sugar vigorously in a complex medium under strictly anaerobic condition, indicating that the nutritional requirement for anaerobic growth was met by the complex-medium components.
Therefore, restriction of oxygen entry into foods and beverages, which are rich in nutrients, is not a promising strategy to prevent the risk of spoilage by this yeast.
Besides, Leyva et al.
(1999) have reported that "Z. bailii" cells can retain their spoilage capability by producing a significant amount of gas even in non-growing conditions (i.e.
presence of sugars but absence of nitrogen source). 
With a pKa of 4.76, it is about as acidic as acetic acid.
Sorbic acid and its salts, such as sodium sorbate, potassium sorbate, and calcium sorbate, are antimicrobial agents often used as preservatives in food and drinks to prevent the growth of mold, yeast, and fungi.
In general the salts are preferred over the acid form because they are more soluble in water, but it is the acid form that is active.
The optimal pH for the antimicrobial activity is below pH 6.5.
Sorbates are generally used at concentrations of 0.025% to 0.10%.
Adding sorbate salts to food will, however, raise the pH of the food slightly so the pH may need to be adjusted to assure safety.
It is found in many other foods, such as cheeses and breads.
The E numbers are:  E200 Sorbic acid  E201 Sodium sorbate  E202 Potassium sorbate  E203 Calcium sorbate Some molds (notably some "Trichoderma" and "Penicillium" strains) and yeasts are able to detoxify sorbates by decarboxylation, producing "trans"-1,3-pentadiene.
The pentadiene manifests as a typical odor of kerosene or petroleum.
Other detoxification reactions include reduction to 4-hexenol and 4-hexenoic acid.
Sorbic acid can also be used as an additive for cold rubber, and as an intermediate in the manufacture of some plasticizers and lubricants. 
The pH level of a wine is the measurement of the amount of free (H+) hydrogen ions.
It is related to the titratable acidity level of a wine but differs in significant ways.
Low pH numbers indicate a high concentration of acids in a solution.
While pure water is neutral with a pH of 7, wine tends to be more acidic with a pH between 3 and 4.
As the acid levels in ripening grapes fall, the concentration of acids are lessening which means the pH level is rising.
Yeasts, bacteria, phenolic compounds such as anthocyanins which influence color all have varying tolerance to wines with high pH levels.
In general, wines with high pH value tend to have duller colors and less developed flavors and be more prone to wine faults caused by spoilage organisms which makes monitoring the pH levels of grapes during ripening a priority for viticulturists and winemakers.
While the rudimentary method of testing pH is to expose the grape juice to a pH indicator such as the strips used for a standard litmus test, the results are usually not as detailed and accurate as what is needed to evaluate ripeness.
Therefore, most wineries will us a pH meter that can give readings to an accuracy of plus or minus 0.1.
As with sugars and acids, the ideal pH levels to determine ripeness will vary.
For white wines, winemakers often look for pH readings between 3.1 and 3.2, while would be a maximum of 3.4.
If the pH is too high, it may be a sign that the grapes are overripe (or that the soil has too much potassium which will also influence pH readings).
While there are risks to letting the pH go too high, winemakers can counter high pH by adding more tartaric or malic acid during the winemaking.
However many viticulturists and winemakers uses pH readings as a strong boundary line for when to start the harvest. 
Yeasts are chemoorganotrophs, as they use organic compounds as a source of energy and do not require sunlight to grow.
Carbon is obtained mostly from hexose sugars, such as glucose and fructose, or disaccharides such as sucrose and maltose.
Some species can metabolize pentose sugars such as ribose, alcohols, and organic acids.
Yeast species either require oxygen for aerobic cellular respiration (obligate aerobes) or are anaerobic, but also have aerobic methods of energy production (facultative anaerobes).
Unlike bacteria, no known yeast species grow only anaerobically (obligate anaerobes).
Yeasts grow best in a neutral or slightly acidic pH environment.
Yeasts vary in what temperature range they grow best.
For example, "Leucosporidium frigidum" grows at , "Saccharomyces telluris" at , and "Candida slooffi" at .
The cells can survive freezing under certain conditions, with viability decreasing over time.
In general, yeasts are grown in the laboratory on solid growth media or in liquid broths.
Common media used for the cultivation of yeasts include potato dextrose agar or potato dextrose broth, Wallerstein Laboratories nutrient agar, yeast peptone dextrose agar, and yeast mould agar or broth.
Home brewers who cultivate yeast frequently use dried malt extract and agar as a solid growth medium.
The antibiotic cycloheximide is sometimes added to yeast growth media to inhibit the growth of "Saccharomyces" yeasts and select for wild/indigenous yeast species.
This will change the yeast process.
The appearance of a white, thready yeast, commonly known as kahm yeast, is often a byproduct of the lactofermentation (or pickling) of certain vegetables, usually the result of exposure to air.
Although harmless, it can give pickled vegetables a bad flavor and must be removed regularly during fermentation.