Wine preservatives are used to preserve the quality and shelf life of bottled wine without affecting its taste. Specifically, they are used to prevent oxidation and bacterial spoilage by inhibiting microbial activity. Wine contains natural preservatives such as tannin, sugar and alcohol, and can be preserved through physical preservation methods, such as storage at an appropriate temperature. However, bacterial growth is still possible, so chemical preservatives are added to most wines. Typical chemical preservatives include sulfur dioxide and its related chemicals, such as sulfites. The use of preservatives in wine has been shown to cause health problems in some consumers. Deterioration Despite the alcohol in wine, growth of bacteria is possible, even when completely fermented. Wine is made from the fermentation of grape juice, which contains sugar. During the fermentation process, yeast will convert sugar into alcohol. If the fermentation is not complete, the wine will contain residual sugar content. The sugar acts as nutrient needed for the growth of bacteria, which can deteriorate the wine or even turn it into grape vinegar. Because the alcohol content of wine is relatively low, the alcohol cannot completely inhibit the proliferation of bacteria. Long-term improper storage may accelerate deterioration. During the brewing process, microbial spoilage can lead to the deterioration of wine quality and taste, making it unhygienic and unacceptable to consumers. The main bacterial groups are yeast, candida and Hanseniaspora. In addition, microbial diseases of wine are mainly caused by yeast, lactobacillus and acetic acid bacteria. This is because yeast may re-ferment a wine with high sugar content, making it cloudy and impure. Lactic acid bacteria can cause acid spoilage in dry wine with low acidity and lactic acid bacteria disease in sweet wine with low acidity. Acetic acid bacteria may cause the increase of volatile acid in wine, resulting in an undesirable sour vinegar taste. These fungi are all bad for the safety and flavor of wine. Preservatives Anything that extends the shelf life of red wine is considered a preservative. Preservatives are mainly divided into natural preservatives and chemical preservatives. Natural preservatives Tannins Tannins, also known as polyphenols, are found in the xylem, bark, leaves, fruits and roots of plants. Tannin molecules undergo polymerization to join into longer molecules and turn it into a "protective colloids" that prevents or limits aggregation, flocculation and step haze formation and precipitation. At the same time, tannins are also one of the main