Out-of-control yeast
These single-celled fungi are often purposefully added to food. Feeding on sugars, the cells release carbon dioxide, which is beneficial for the baking of dough, as it makes it rise. Although a little yeast in food is good for you, when uncontrolled growths of yeast enter the body, it can cause infection. Different strains of yeast can tolerate different acidities in food, but yeasts are typically the most prevalent microbe for spoiling carbonated products such as fizzy drinks. This is due to their ability to survive in environments of very low ph and high carbonation. By producing ethanol as a waste product, spoilage yeasts can drastically change the taste of drinks it contaminates. It can also eat away at preservatives, which further reduces the shelf life of food and drink.