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Typing and differentiation

As discussed above, brewing strains can be regarded as the main driving force in the production of beer. In addition to the other main raw materials (e.g. barley malt, hops, and water), yeast determines the flavour and character of beer. For example, wort pitched and fermented with three different brewing yeast strains will result in three different beers. Therefore, depending on the degree ofstrain-related genetic and phenotypic attributes, beer profiles can vary considerably. A practical way of comparing and differentiating strains is to perform standardized small-scale pilot fermentations. These can be followed up by sensorial and chemical analyses, which can be tailored according to the specific aim ofyeast performance, optimization, aroma, and flavour characteristics of the final beer. General screening programs of brewing yeast strains usually follow a much broader approach, with a logical first step aiming at species identification, followed by the implementation of a DNA-based typing method that generates a strain fingerprint appropriate for strain discrimination. Afterwards or in parallel, a broad variety of phenotypic methods can be applied to characterize strain-specific fermentation behaviour and to highlight strain-specific key metabolic components. Nowadays, there is a tendency to use high throughput systems (Steensels et al., 2014) and miniature platforms (e. g. multiwell plate systems) to increase screening efficiency (Greetham, 2014). Those systems can be used to quickly generate an overall picture of yeast strain performance and to identify important strain-specific metabolic pathways and key products. Selected phenotypic and DNA-based methods for yeast species and strain discrimination are listed in Table 4.3 and are evaluated according to their practical importance for brewing.

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