[11] Besides the asexual reproduction mode, under certain conditions (e.g. nutritional stress) Z. bailii produces sexual spores (ascospores) in a sac called ascus (plural: asci).

[12] On various nutrient agars, Z. bailii colonies are smooth, round, convex and white to cream coloured, with a diameter of 2 – 3 mm at 3 – 7 days.

[14] Among the Zygosaccharomyces spoilage species, Z. bailii possesses the most pronounced and diversified resistance characteristics, enabling it to survive and proliferate in very stressful conditions.

The most frequently described natural habitats are dried or fermented fruits, tree exudates (in vineyards and orchards), and at various stages of sugar refining and syrup production.

[4] Besides, it is seldom to encounter Z. bailii as a major spoilage agent in unprocessed foods; usually the yeast only attains importance in processed products when the competition with bacteria and moulds is reduced by intrinsic factors such as pH, water activity (aw), preservatives, etc.

[4] Besides being preservative resistant, other features that contribute to the spoilage capacity of Z. bailii are: (i) its ability to vigorously ferment hexose sugars (e.g. glucose and fructose), (ii) ability to cause spoilage from an extremely low inoculum (e.g. one viable cell per package of any size), (iii) moderate osmotolerance (in comparison to Zygosaccharomyces rouxii).

Therefore, restriction of oxygen entry into foods and beverages, which are rich in nutrients, is not a promising strategy to prevent the risk of spoilage by this yeast.

[27] Besides, Leyva et al. (1999)[28] have reported that Z. bailii cells can retain their spoilage capability by producing a significant amount of gas even in non-growing conditions (i.e. presence of sugars but absence of nitrogen source).

As the pump requires energy to function optimally, high sugar levels enhance Z. bailii preservative resistance.

[33] Indeed, Warth (1989)[31] has reported that the uptake rate of propionic acid by diffusion in Z. bailii is much lower than in other acid-sensitive yeasts (e.g. Saccharomyces cerevisiae).

[33] Another mechanism of Z. bailii to deal with acid challenge is that the yeast uses a plasma membrane H+-adenosine triphosphatase (H+-ATPase) to expel proton from cells, thereby preventing intracellular acidification.

[34] In addition, Cole and Keenan (1987) [32] have suggested that Z. bailii resistance includes an ability to tolerate chronic intracellular pH drops.

[10] Fermentation of sugars (e.g. glucose, fructose and sucrose) is a key metabolic reaction of most yeasts (including Z. bailii) when cultured under facultative anaerobic conditions.

Principally, these sugars are converted to ethanol and CO2, causing the products to lose sweetness and acquire a distinctive alcoholic aroma along with gassiness.

[42] In addition, Z. bailii can also oxidatively degrade sorbate and benzoate (and use these compounds as a sole carbon source), while S. cerevisiae does not have this capability.

[43] According to Thomas and Davenport (1985),[5] early reports of spoilage in mayonnaise and salad dressing due to Z. bailii date back to the beginning of the 20th century.

Around the same time, fermentation spoilage incidents occasionally appeared in fruit syrups and beverages preserved with moderate benzoic acid levels (0.04 - 0.05% (w/w)).

Z. bailii is also well recognized as one of the main spoilers in wines due to its high resistance to combinations of ethanol and organic acids at low pH.

[44] Furthermore, the spoilage by this yeast has been expanding into new food categories such as prepared mustards,[45] fruit-flavoured carbonated soft drinks containing citrus, apple and grape juice concentrates.

[5] It has been reported that growth of Z. bailii also results in significant gas and ethanol formation, causing a typical alcoholic taste.

[46] Apart from spoiling foods, as a direct consequent of growth, Z. bailii can modify the product texture and composition such that it may be more readily colonized by other spoilage microorganisms.

Apart from unwanted spoilage, this yeast is also present in the fermentation of traditional Italian balsamic vinegar (Zygosaccharomyces rouxii together with Zygosaccharomyces bailii, Z. pseudorouxii, Z. mellis, Z. bisporus, Z. lentus, Hanseniaspora valbyensis, Hanseniaspora osmophila, Candida lactis-condensi, Candida stellata, Saccharomycodes ludwigii, Saccharomyces cerevisiae)[48]