Part II: The influence of the serial repitching of Saccharomyces pastorianus on the uptake dynamics of amino acids during the fermentation of barley and gluten-free buckwheat and quinoa wort

The present paper is part of a comprehensive study regarding the influence of the serial repitching of Saccharomyces pastorianus TUM 34/70 on the composition of the barley, buckwheat and quinoa fermentation medium. In particular, it focuses on the uptake dynamics of amino acids during 11 successive fermentations. Samples were taken every 20h after pitching, analysed for the particular amino acid content and statistically evaluated. The term 'completion time' (t₉₅), here defined as the percentage attenuation time necessary for ~95% of the total assimilation, has been introduced. In addition, 'the serial repitching factor' is used for the first time to support the visual evaluation of the influence of serial repitching. Amino acids that were essentially affected by serial repitching were glutamine, arginine, alanine and tryptophan in barley, aspartate, glutamate and tryptophan in buckwheat, and all in the quinoa wort fermentation. As opposed to buckwheat and quinoa, in barley the amino acids behaved more or less independently from each other, which for buckwheat and quinoa indicates a more general systemic change in the yeast. From the amino acids point of view, buckwheat can be fully regarded as a suitable gluten-free substitute for barley beer since the amino acid assimilation was very consistent and hardly influenced by the serial repitching, especially regarding the final amino acid assimilation. In the case of quinoa, the assimilation of all amino acids became significantly affected after the sixth fermentation and quinoa is probably unsuitable for the production of beer-like beverages. Results suggest no substitutional potential of quinoa for barley beer, but if a nutrient-rich beverage of choice from quinoa malt is intended to be prepared, it seems that the serial repitching is limited to six fermentations at most.