Part III: the influence of serial repitching ofSaccharomyces pastorianuson the production dynamics of some important aroma compounds during the fermentation of barley and gluten-free buckwheat and quinoa wort

Abstract

The present paper is the last report of a comprehensive study regarding the influence of the serial repitching of Saccharomyces pastorianus TUM 34/70 on the composition of a barley, buckwheat or quinoa fermentation medium. In particular, it focuses on the production dynamics of important volatile compounds typically associated with the aroma of beer. Samples were taken every 24 h after 11 serial repitchings of a single starter culture, analysed for the particular aroma compound content by distillation followed by gas chromatography with flame ionization detection. The term 'serial repitching factor' is used for the first time to support the visual evaluation of the influence of serial repitching. Results showed that the levels of methanol in the quinoa wort fermentation were only slightly higher than in barley and in practical terms independent of successive fermentation. The behaviour of acetaldehyde in quinoa was similar to that in barley. However, there was a final 2-fold lower production of some important aroma compounds compared with barley and buckwheat and for this reason quinoa cannot be recommended as a gluten-free substitute to produce a bottom-fermented beer. Regarding the buckwheat wort fermentation, a 2-to 3-times lower final acetaldehyde content than in barley is desirable, whereas a relatively high methanol content is not desirable. Barley and buckwheat showed comparable sum concentrations and similar overall profiles of some important aroma compounds. From this perspective, buckwheat appears to be a promising substitute for barley as a brewing raw material. The overall conclusions of our comprehensive study (Parts I-III) are that buckwheat shows adequate brewing properties to substitute for barley in the commercial preparation of a bottom-fermented gluten-free beer-like beverage, and yeast can be repitched at least 11 times. In contrast, quinoa in practical terms shows no substitutional potential for barley in beer; however, it has many nutritious advantages, thus the commercial preparation of a unique, bottom-fermented gluten-free 'non-beer-like' beverage -where the yeast could be repitched six times at most -appears feasible.

Comparison of sensory and chemical evaluation of lager beer aroma by gas chromatography and gas chromatography/mass spectrometry

“…In general, we can conclude that samples classified as less appropriate are richer with volatiles than those with appropriate sensorial scores. Surplus concentrations of volatiles can impair on the organoleptic perception of beer . For samples 16 and 22, there is also a characteristic absence of 4‐deceonic acid ethyl ester.…”

Recent innovations in the production of selected specialty (non-traditional) beers

“…Successful beer brewing using 100% buckwheat malt has been reported (Phiarais et al 2010). Buckwheat has sufficient brewing properties to be used as a brewing raw material and exhibited substitutional potential for barley in the commercial preparation of a bottom-fermented gluten-free beer-like beverage (Deželak et al 2015). Liu et al (2013) investigated changes in phenolic and flavonoid contents of tartary buckwheat beer during fermentation.…”

Suitability of unmalted quinoa for beer production

“…Indeed, the Food and Agriculture Organization of the United Nations lists quinoa as 1 of 11 cereals / pseudocereals of interest to brewers . Being a gluten‐free raw material, quinoa has been investigated for brewing gluten‐free beer . However, quinoa malt has a very low hydrolytic enzyme content in comparison to barley malt, which requires the use of exogenous enzymes .…”

“…7 Being a gluten-free raw material, quinoa has been investigated for brewing gluten-free beer. [8][9][10][11][12][13] However, quinoa malt has a very low hydrolytic enzyme content in comparison to barley malt, which requires the use of exogenous enzymes. 14 Moreover, to avoid unpleasant bitterness, the outer seed coat of quinoa containing saponins must be removed.…”

“…Although there have been reports of quinoa malt being used to produce gluten-free beer, [8][9][10][11][12][13] no detailed studies have been conducted on the processability of unmalted quinoa. This www.soci.org E Kordialik-Bogacka et al…”