# Microbial Dynamics in Sour-Sweet Wine Vinegar: Impacts on Chemical and Sensory Composition
## 1 Introduction
All of the mass is maintained in a continuous state of agitation, allowing an easy transfer of oxygen from the medium to the bacteria. This prevents _Acetobacter_ cell death and promotes efficient microbial growth [10]. Hence, the necessities for submerged processes are the availability of ethanol, continuous aeration, and acetic acid bacteria strains tolerant to high concentrations of acetic acid and ethanol that require small amounts of nutrients and are not sensitive to phage infections [10]. This last requirement is important once phage infections impact AAB growth and, consequently, acetic acid production. Phages, also known as bacteriophages, are viruses that infect and replicate within bacterial cells. They specifically target and infect bacteria, including AAB, resulting in the lysis (bursting) of cells, leading to a decline in population, a disruption in their metabolic activity, and a decrease in acetic acid production [11; 12]. Phages that infect AAB have been isolated from various sources, including vinegar production facilities, fruit juice processing plants, and natural environments. These phages can have a significant impact on industrial vinegar production, leading to decreased productivity, spoiled batches, and economic losses in vinegar production [11]. One major disadvantage of the submerged method is the amount of heat generated and the lack of temperature control. Acetic acid fermentation is an exothermic process, meaning it releases heat as a byproduct. In submerged systems, heat accumulation can be an issue, leading to increased temperature, which may negatively affect bacterial growth and acetic acid yield. Proper temperature control becomes crucial to maintaining optimal conditions [10]. In terms of organoleptic drawbacks, in submerged fermentations, due to stirred conditions, the liquid creates foam, leading to the establishment of a reducing environment that compromises the acidification process [10]. Also, as acetic acid production progresses, the fermentation medium can become more viscous due to the accumulation of acetic acid and bacterial biomass. The increased viscosity can hinder efficient mixing and oxygen transfer, further impacting the fermentation process [13]. Contrasting submerged methods, the vinegar produced by traditional methods (Orleans or French method) is generally considered to be of high quality, both chemically and sensorially, due to the balance between organic acids and amino acids achieved through long-term surface culture fermentation [2]. However, in the traditional method, there is no microbial control, which delays the alcoholic fermentation (AF) and the acetic acid fermentation (AAF), causing contamination and low acidity. Therefore, it is important to understand the interactions between acetic acid bacteria and yeasts to promote strategies that can allow a faster and higher acidity yield fermentation while being able to maintain quality, regardless of the method used. One type of vinegar produced by wine acidification where yeasts and bacteria co-exist and produce savory vinegar is traditional balsamic vinegar (TBV), which originated in Modena and Reggio Emilia, Italy. In Spain, fortified sherry, with its distinctive nutty and oxidized flavor [14], has also been used for vinegar production. In Portugal, sour-sweet wine vinegar has recently emerged. Port wine vinegar has been produced by some wine companies since 2018. It has been described as having \"a robust and naturally fruity flavor accented by a slight hint of acidity and a deep shade of ruby red.\"  
Thus, in this review, we analyze the balsamic acetification system and the possible interactions between acetic acid bacteria and yeasts that occur during vinegar production, considering the positive features of a diverse microbiota, such as glucose and ethanol tolerance, alcohol and aldehyde dehydrogenase formation, thermotolerance, acetate and ethanol oxidation, the capability to grow in different acetic acid concentrations, and aroma compound production [15].