Causes of Spoilage
Winemakers will be familiar with the causes of spoiled wine and while we are not likely to encounter them in making beers, cider, meads and other alcoholic drinks, it is as well to know about them. We are then able to understand why precautions against them are so necessary.
Spoilage in meads and ciders, etc., is covered in their respective chapters. Here I am concerned only with spoilage in beers and how to prevent it. In beer making, risk of spoilage is quite remote. This is because any wild yeasts or bacteria on the ingredients are destroyed during the boiling of the wort.
Risks of contamination of the wort by yeasts and bacteria floating about in the air is also remote. This is because covering vessels as directed prevents them reaching the wort. If the vessels are not covered as directed, wild yeast and bacteria may reach the wort to turn it insipid and Hat, oily or vinegary. Leave a bottle of beer or one with a drop left in the bottom opened for a few days and then smell it and the chances are that it will smell of vinegar. This is evidence that the vinegar bacteria has been at work on the alcohol and turned it to acetic acid - otherwise, vinegar. If this bacteria, or others or many of the wild yeasts in the air are allowed to come into contact with the beer, then calamity is in the offing.