# Microbial Dynamics in Sour-Sweet Wine Vinegar: Impacts on Chemical and Sensory Composition
## 1 Introduction  
Vinegar production dates back to at least 200 BC and is an example of microbial biotransformation. Vinegar can be made from any fermentable sugary substrate and is a globally famous acetic acid condiment produced with dual fermentation (alcoholic and acetic). It possesses a pleasantly sour flavor and has been used as a diet condiment, food preservative, and remedy for people and animals [1]. The most known and traditional vinegar is the one that is made from wine. In the old days, wine vinegar production was considered a chemical process. In 1732, the Dutchman [PERSON] specified that the \"mother of vinegar\" was a living organism [1]. However, it was only in 1864 that [PERSON] claimed that the conversion of wine into vinegar was due to the development of the veil of _Mycoderma aceti_ on the wine's surface [1]. The methods for producing wine vinegar involve the use of grape must, which goes through alcohol fermentation followed by ethanol oxidation to acetic acid [2]. These biochemical processes are carried out in sequence by yeasts and acetic acid bacteria (AAB), which produce acetic acid, and several metabolic compounds responsible for the taste and flavor of vinegar, such as nonvolatile compounds (sugars, organic acids, amino acids) and volatile compounds (esters, aldehydes, among others) [3]. Wine vinegar can be differentiated by its production systems and technologies; there are two types of techniques used to produce vinegar. The slower traditional processes andthe quick submerged (industrial purpose) methods. In traditional vinegar, produced by the so-called Orleans or French method, the oxidation of ethanol into acetic acid occurs due to a static culture of AAB at the interface between the liquid and air. Usually, oak casks are used to produce this kind of vinegar, once the wood allows for continuous aeration of the acetic bacteria culture. This is the case with vinegars such as Jerez/Xferes/sherry, where the oak used is _Quercus alba_ (American oak), and it takes a minimum of six months in wood for the vinegar to be considered a sherry vinegar [4]. The wood barrels are filled to 2/3 capacity, have holes on the sides for air passage, and a funnel with an extension to the base of the barrel, allowing the wine to be added at the bottom and preventing the alteration of the biofilm formed by the AAB on the surface [5]. In the 18 th\(-\)19 th century, [PERSON] (1793-1869) developed a dynamic acidification system called the \"German rapid acetification system.\" This process of acetification was industrialized and was named \"Rundpump\" (round pump) because the wine passed through wood shavings that were continuously sprinkled with the mash by a circulation pump and a rotating sprinkler. The wood shavings served as a support for the bacteria. Alternative materials such as bines, maize cobs, or rushes are cheaper than beechwood but not as efficient [6; 7]. Advances in technology allowed the development of the submerged fermentation process, first used to produce antibiotics and, subsequently, vinegar, thanks to computerization. The Frings Acetator is an example of this advance. Annual production is half a million liters of vinegar at 10% acidity [6; 7]. The submerged culture technique involves growing AAB in a liquid medium containing ethanol or other suitable carbon sources. This method is often used in laboratory-scale studies and industrial settings for large-scale acetic acid production. In submerged culture, the liquid medium is typically agitated to enhance oxygen transfer, which provides fast and efficient aeration [8]. According to [PERSON] and co-workers [9], in this system, a non-rotating stator supports a hollow-body turbine. Radial holes, which open in the opposite direction of rotation, allow air from outside to be released inside, resulting in very fine air bubbles. A homogenous air-liquid emulsion is formed, which is pushed upwards and diverted by deflectors.