Vinegar processing
Vinegar is the result of two stages of fermentation. Yeast converts sugars into ethanol anaerobically in the first stage. In the second step, bacteria from the genera Acetobacter and Gluconobacter oxidize ethanol to acetic acid aerobically. The residual ethanol content in wine vinegar must be less than 0.5% and less than 1% in other vinegars.
Vinegar is an aqueous solution of acetic acid, typically containing 3-5% acetic acid, and is produced by a double fermentation: simple sugar is converted to ethanol using yeast, and ethanol is then converted to acetic acid by acetic acid bacteria. Common commercial types include white vinegar, apple cider vinegar, balsamic vinegar, wine vinegar, rice vinegar and malt vinegar, each defined largely by the raw material entering the first fermentation.
The two-step biochemistry governs the whole plant layout. In alcohol fermentation, yeast enzymes use the sugar present in the fruit to produce alcohol (ethanol) and carbon dioxide gas: sugar (fructose, glucose) gives ethanol + 2CO2. In acetic acid fermentation, the alcohol produced reacts with atmospheric oxygen through the action of acetic acid bacteria to produce acetic acid and water: ethanol gives acetic acid + H2O. Because the second stage depends on oxygen transfer, aeration and bacterial culture management are the critical control points of the fermentation hall.
The process route runs from harvesting through washing and grading, mashing, settling, fermentation and ageing, to bottling. Downstream of fermentation, vinegar produced by the quick process is kept for ageing for about six months. It is then clarified so that the vinegar is made sparkling clear before bottling, and pasteurised by heating in an open vessel to about 60 degree C, after which it is cooled and bottled.
Spoilage is a live risk in vinegar production: lactic acid producing bacteria grow initially and spoil the vinegar, so hygienic design, culture control and timely pasteurisation matter as much as fermenter sizing. PMG Engineering delivers end-to-end engineering design and construction management projects in the food and beverage industry, covering process engineering, project management, automation, food safety, and mechanical and electrical.