Spoilage of Stored, Processed and Preserved Foods

It is trite to say that dried foods must be kept dry, heat processed foods must be heated enough to inactivate all relevant spores and preservative concentrations must be high enough to inhibit all fungi. In reality, the science of preserving foods, like so many other disciplines, requires compromise. Really dry foods, i.e. of a safe a_w, may be impossible to obtain for climatic or economic reasons or be unacceptable to the consumer; a sufficient heat process may destroy desirable flavours; and permitted preservative levels are set by law. Some fungi, by virtue of specific attributes, simply cannot be processed out of certain types of foods. Of particular importance are Xeromyces bisporus and Zygosaccharomyces rouxii – extreme xerophiles which grow in concentrated foods; Byssochlamys spp., Talaromyces spp. and Neosartorya fischeri with ascospores of very high heat resistance which can survive heat processing and grow in heat processed acid foods; and Zygosaccharomyces bailii, a preservative resistant yeast. Making foods safe from these fungi requires that they be absent from raw materials or destroyed by pasteurisation and then excluded from the processing and packing lines.