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W eknowthatyeastpropagates itselfinfermentationthrough a cellular growth known as yeast budding to form new cells. During this process the yeast does not undergo vast genetic changes, which allows it to remain (more or less) consistent from generation to generation in fermentations. However, when yeast is exposed to stressfulenvironments,itstartstoreproduce sexuallyviathemeansofsporulation.Spores allow the yeast to survive harsh conditions and recombine later when conditions become favourable. Yeast biologists then use a directed evolution approach to try their own re-combinations of yeast. This can enhance the genetic diversity amongst domesticated brewing strains in the hopes to solve specific problems without the use of GMO technologies. BREEDING IN BREWING…AND ELSEWHERE Domestic pets such as cats and dogs were bred over centuries to achieve the plethora of breeds we have today with their different traits. From the Labrador bred for its intelligence to be an adept guide dog, to the Bloodhound with its acute scent-tracking abilities, the possibilities are endless due to selective breeding. Similarly, plant breeders developed hop and barley cultivars to not only give a diverse range of flavours and aromas in beer but also to achieve the following for commercial purposes: • Yield • Pest resistance • Higher protein content The process is usually slow as plants tend to follow an annual season and require eight or more years before enough research and testing is conducted to commercialise a new “breed”. APPLICATIONS FOR YEAST Yeast has a faster growth cycle than plants and animals. This allows for an immense amount of data in testing and research to be generated in a matter of months, and for thousands of variations to occur. Indeed, there are many strains (or breeds) of yeast that are available to the brewer depending on the use case. From American West Coast or British Ale strains to Belgian Saison strains, the yeasts seem similar under the microscope but are in fact incredibly different in how they operate in beer fermentation. General parameters in beer yeast that are of interest for us to target are the following: • Attenuation • Flocculation • Fermentation speed • Flavour and aroma • Sulphur mechanisms • Stress tolerance • Temperature tolerance • Different enzymatic activity HOW YEAST IS BRED Yeast can sporulate and “breed” naturally in the wild (or in the brewery), which allows us to always stumble upon new strains or “hybrids” to exploit when we wish to look for them. However, nowadays breeding is often induced under laboratory conditions. Two parental strains are induced to sporulate, hybridise and produce an array of new strains called hybrids for us to look at. Sporulation When certain yeasts are in stressful conditions, they will undergo meiosis to form spores. Each spore contains a randomised set of chromosomes during the “genetic halving” from a process called recombination, which happens during meiosis. These spores are highly resistant to harsh environmental factors and allow for yeast survival when exposed to them. Stressful conditions that induce sporulation include desiccation, low nitrogen and low sugar. After sporulation, the spores germinate into daughter cells that contain half of the genetic potential of the parental cell. These daughter cells are capable of mating or budding. Selecting mating types Yeasts have two different mating types, namely α (alpha) types and a-types, very much like how male and female genders are prevalent in other organisms. Only opposite mating types are compatible in mating, meaning that an α -type can only mate with an a-type. Hybridisation When physically close together, the yeast can detect mating pheromones that are produced from their counterpart, which triggers the hybridisation process. Labs have highly specialised equipment that can physically pick up a daughter cell and place it next another of the opposite mating type. The cells move towards each other and come into physical contact in a process known as “shmooing”. This enables them to fuse into a new diploid cell known as a hybrid strain. These hybrids contain half the genetic material from both parents to make up a new (and unique) set of genetic potential. Screening The different hybrids are then screened against the parameters we are looking for. Does it likewarmer or colder temperatures? Is it one of the fastest fermenters? Does it produce low concentrations of dihydrogen sulphide (H 2 S)? Is the best saison flavour retained but does not digest dextrin like other diastatic strains? These are all examples of questions that could be answered through testing the hybrids and earmarking the best performers. Sporulation Germination Haploid DaughterCells Spores Desiccation Low Nitrogen Other Stress Low Sugar a a “Shmooing” a a Haploid Cells Proximity Cell Fusion Nuclear Fusion ontapmag.co.za | Winter 2022 | 45