An overview of microorganisms and factors contributing for the microbial stability of carbonated soft drinks

• Microbiological aspects of soft drinks are discussed.
• Main microbial groups of importance are presented.
• Key factors contributing for the microbial stability of soft drinks are reviewed.
• Measures to ensure microbial stability of soft drinks are commented.

Soft drinks, which are largely produced and consumed worldwide, are acidic beverages (pH 2.5–4.0), formulated with water, sucrose, carbonated with 1.5–5.0 volumes of CO2, and added or not with chemical preservatives and fruit juices. A simplified manufacturing process of soft drinks consists of water treatment, production of simple syrup, production of compound syrup, carbonation and filling. As any other food and beverage, soft drinks can be contaminated by microorganisms; however, the low pH caused by the addition of acidulants, the presence of preservatives, and the presence of CO2 comprise major barriers to microbial growth. Because of these characteristics, filamentous fungi and some bacteria, including pathogens, do not pose spoilage and safety risks for soft drinks. On the other hand, because of their tolerance to acidic environments and CO2, both yeasts and aciduric bacteria can survive and deteriorate soft drinks. This review deals with the microorganisms of relevance, as well as with the factors influencing their survival and role on soft drink spoilage.