# Microbial Dynamics in Sour-Sweet Wine Vinegar: Impacts on Chemical and Sensory Composition
## 6 Wine Yeasts and Acetic Acid Bacteria Interactions
### Abiotic Interactions  
In vinegar production, abiotic interactions refer to non-living factors or processes that influence the production process or the quality of vinegar. The primary abiotic interaction in vinegar production is the fermentation process, where AAB converts ethanol into acetic acid in the presence of oxygen. Oxygen is typically provided through aeration systems or by allowing air exposure to the fermenting liquid [9; 13]. While a sufficient oxygen supply is necessary to support the AAB's growth and metabolism, insufficient oxygen can result in slower fermentation or the growth of undesirable microorganisms. For yeasts, excessive exposure to oxygen can be detrimental. High levels of oxygen can cause oxidative stress, leading to the formation of ROS (reactive oxygen species) that can injure cellular components, including DNA, proteins, and lipids. This oxidative damage can inhibit yeast growth and viability [110; 111]. However, in some cases, oxygen increases yeast viability by increasing sterol and fatty acid biosynthesis. The Crabtree effect has been observed in TBV species, such as _Z. bailii_ and _S. cerevisiae_, but not in _Candida_ spp., which, in aerobic conditions, respire sugars. Hence, if the dominant species in cooked must are Crabtree-negative yeasts, the oxygen level may negatively affect ethanol production [16]. Osmotic stress caused by sugar concentration is also a biotic stress that must be considered. Some yeast species are less affected by increases in sugar content in cooked must, namely, _Zygosaccharomyces_ spp. And _Candida_ spp. Strains, which can produce the highest ethanol concentration at the highest sugar value. On the other hand, _S. cerevisiae_ strains isolated from TBV were shown to be more sensitive to the high sugar concentration [16]. Temperature plays a significant role in vinegar production as it affects the growth and activity of AAB. These bacteria thrive in a temperature range of 25-30/35 degrees Celsius [78]. Lower temperatures can slow down fermentation, while higher temperatures can lead to the growth of unwanted microorganisms, affecting the quality of vinegar. However, in other symbiotic products such as Kombucha, where we can also find symbiotic microbial consortia of yeasts, acetic acid bacteria (AAB), and occasionally lactic acid bacteria, the effects of temperature in fermentation, product shelf life, and microbial prevalence have already been studied [112]. For vinegar, namely, symbiotic vinegar such as TBV, the literature on the subject is scarce. However, [PERSON] and [PERSON] [16] mention that during the full-fementation phase, exothermal metabolic reactions raise the temperature, which sometimes rises above 40 \({}^{\circ}\)C, leading to a reduction in yeast vitality independent of the species present in the fermentation vessel. Hence, while AAB thrives at those temperatures,yeast may stop fermenting, leading to stuck fermentations and a decrease in ethanol for AAB. Interestingly, the resistance of AAB to high temperatures was also found in other vinegar productions. Seven AAB (all _A. pasteurians_) that tolerated temperatures above 40 \({}^{\circ}\)C and ethanol above 10% (\(v/v\)) were isolated from Chinese vinegar Pei (a moistened solid mixture of alcohol, wheat bran, rice hull, water, and vinegar seeds), showing that the isolated strains could be useful for other fermentations besides TBV, such as submerged fermentation processes [113]. [PERSON] and co-workers [114] were able to thermally adapt the _A. pasteurians_ K-1034 strain, capable of performing acetic acid fermentation in moromi rice (the industry standard term for the fermenting mixture, yeast, koji, steamed rice, and water for brewing), by experimental evolution using a \"pseudo\" rice moromi culture. The adapted strain was able to grow up to 40 or 39 \({}^{\circ}\)C.  
The ability of AAB to use less biomass to produce large amounts of acetic acid compared to other bacteria that also produce organic acids (such as LAB) may be considered the greatest strength of AAB [115].