# Microbial Dynamics in Sour-Sweet Wine Vinegar: Impacts on Chemical and Sensory Composition
## 5 Fortified Wines and Fortified Vinegar
To make fortified sherry wine vinegar, high-quality wine is selected and then transferred to oak barrels. The barrels are partially filled to allow for the formation of the acetic acid bacteria film, and the quality of vinegar is heavily determined by the specific wooden casks used for its aging [92]. After acetic acid bacteria inoculation, the wine is then allowed to acetify, and this process can take several months to a few years, depending on the desired flavor profile of the vinegar. Once the wine has been acetified, the resulting vinegar is aged in oak barrels for a minimum of six months to allow it to develop its unique flavor and aroma characteristics. The longer the vinegar is aged, the more complex and intense its flavor becomes [92]. Port wine vinegar is often described as having a rich, sweet flavor with a hint of acidity. It is commonly used in salad dressings, marinades, and sauces, and can also be used as a substitute for other types of vinegar in recipes. One difficulty in the acetification process is the control of oxygen levels. Oxygen can accelerate the acetification process, leading to an excessively acidic wine, or it can slow down the process, resulting in a wine with insufficient acidity. The use of oxygen-permeable membranes and careful control of the wine's exposure to oxygen can help maintain optimal oxygen levels during the acidification process [93]. For port wine acidification, the major constraint may be the wine alcohol content (usually higher than 19%, \(v/v\)). According to [PERSON] et al. [22], AAB having a unique set of alcohol dehydrogenase enzymes that are not inhibited by ethanol may be the reason for acetic bacteria's resistance to alcohol content. However, a high concentration of ethanol can inhibit acetic acid bacterial cell growth and then limit acetification fermentation productivity [20,94]. According to the work of [PERSON] [95], the bacteria's acclimatization to the high-alcohol environment will allow for better acidification. Hence, the first stage in the acetification process must be to use wine with a lower alcohol degree and let the bacteria adapt to the fermentation conditions, namely alcohol content, temperature, aeration, and stirring. Another possibility is to dilute the wine with distilled water, lowering the alcohol content to around 6-7% or the appropriate ethanol content. This last hypothesis will also lower all the pleasant flavor components of the wines and, thus, of the final vinegar. While port wine vinegar is a relatively recent product, cherry vinegar, or Jerez vinegar, has existed since the corresponding wine. Spontaneous high volatile acidities may occur due to the traditional methods of production. If the \"flor\" layer is disrupted or the wine is not properly maintained, it can lead to spontaneously high volatile acidities. The \"spoiled\" wines are separated in standalone cells and aged following the traditional process employed for wines [96]. Consequently, the unplanned wine's acidification may result in high-quality vinegar that is marketed as Protected Denomination of Origin Jerez Vinegar. This enological product is sold in glass bottles of different volumes, but the official label of the DO Council is compulsory to guarantee its origin. According to the exceptional regulations for sherry vinegar, nowadays, wines can be acetified by the Orleans method or by the submerged method, in stainless steel vessels. In the most traditional method, sherry vinegar is elaborated in oak casks, with the acetic acid bacteria inoculated on the surface of the wine once it needs oxygen to metabolize [96]. Long periods are required to obtain a satisfactory degree of acetic acidity. Barrels (500 L volume) are filled to two-thirds of their total volume, and acidification occurs during the aging of wine/vinegar. Once the vinegar is obtained, it remains in the oak barrels to gain the expected chemical and sensory characteristics (Figure 3).