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The beverage industry needs to ensure a high-quality product until the end of shelf life, while consumers demand mild and sustainable preservation methods. These mild preservation methods carry a possible risk to quality, safety and integrity of the products. Strategies to counteract or solve these issues must be effective against all spoilage yeasts.

In this thesis, we study Saccharomyces cerevisiae subsp. diastaticus (S. diastaticus). It is the main fungal cause of spoilage of beer and Radlers in the brewing industry. This yeast was only detected in nature in South America until now. I have identified S. diastaticus from a bark sample for the first time in Europe. So, S. diastaticus was only detected once in nature, while it was present and easily detected in half of the brewery samples. The big question remains; why?

We also looked at the ancestors of the S. diastatic individuals we found. This showed that these individuals did not all have the same ancestor, as was presumed. In short, the "family relationships" are completely different. Additionally, each individual has its own characteristics; some cannot withstand heat treatment (used to pasteurize beer) while others can handle it very well; in addition, we found that inbreeding was very effective to produce heat resistant offspring when selected for this trait. This may also happen in breweries.