Overgrowth, even during extended refrigeration, can produce a slimy surface, rendering the food unappetizing. Molds are also natural contaminants. When considering animals as sources of food, the natural contaminants include organisms associated with the animals, such as Lactobacillus sp. Limiting the growth of these natural contaminants is the goal of food preservation techniques. Food storage procedures must take into account food preservation techniques.
Many microbes prefer a neutral pH for growth.
Procedures such as pickling rely on growth of natural contaminants which produce acid as a by-product of their metabolism, thus lowering the pH below the organism s optimum range, killing the natural contaminant, and prohibiting growth of other organisms. The remaining food product is a very sour food, such as sauerkraut, which keeps for a long time. Before refrigeration technology, pickling procedures were used to store many types of food. Molds are more likely to spoil acidic foods than bacterial species, because molds can tolerate lower pH ranges. As a result, the organism will lose water, limiting its growth metabolism.