11 Microbiology of soft drinks and fruit juices

Soft drinks and fruit juices represent an important market within the food industry. The increasing variety of products being released at a bewildering rate has altered the potential for spoilage problems. Soft drinks are generally nutrientpoor media that are spoiled by relatively few organisms – usually yeasts, and a few acid-tolerant bacteria and fungi. Carbonation shifts the spoilage flora to those organisms tolerant of carbon dioxide. Soft drinks enhanced by the addition of low levels of fruit juice tend to exhibit similar spoilage flora to fruit juices. The use of ever more exotic raw ingredients may lead to the discovery of unusual spoilage organisms in the future. Yeasts in general, and Zygosaccharomyces bailii in particular, remain the key spoilage organisms because of their overall physiology and resistance to organic acid preservatives (Stratford et al., 2000). Microbial problems within soft drinks and fruit juices can be divided into two groups: