Impact of Yeast

Compound Impact of grape variety Source in grape Impact of yeast Role of yeast/bacteria ... 

Swiegers J. H., Ugliano, M., van der Westhuizen, T, Bowyer, P. (2008b) Impact of yeast rehydration on the aroma of Sauvignon Blanc wine. Australian New Zealand Grapegrower Winemaker, 528, 68-71. 

Microbial dynamics during fermentation impact of yeast strain diversity... 

Impact of yeast and bacteria on beer appearance and flavour... 

This chapter is divided into five sections including an introdnction (Section 17.1), impact of yeast on beer appearance (Section 17.2), impact of yeast on beer flavour (Section 17.3), impact of bacteria on beer appearance and flavour (Section 17.4), and future trends (Section 17.5). The emphasis is on the impact of yeast on beer appearance and flavour because more information is available on this topic. Although most of the discussions are centred on the impact of main brewing yeast strains (Saccharomyces cerevisiae and Saccharomycespastorianus) on barley malt-based beers (ale and lager, respectively) (Lodolo, Kock, Axcell, Brooks, 2008 Stewart, Hill, Russell, 2013), references are also made to other yeasts involved in brewing specialty beers derived from both barley malt and other cereal malts. Lactic acid bacteria (LAB) are the focus of discussion with regard to bacterial impact on beer appearance and flavour due to their relatively common occurrences in beers (Menz et al., 2010 Sakamoto Konings, 2003 Suzuki, 2011 Suzuki, Asano, lijima, Kitamoto, 2008). 

Brewing yeasts contribute positively to beer mouth-feel by producing carbon dioxide and foam bubbles. The impact of yeasts on beer taste varies with the yeasts involved in beer fermentation. In the spontaneous fermentation of acidic beers such as lambics, the mn-Saccharomyces brettanomyces yeasts can ferment malto-oligosaccharides that... 

Relative to the impact of yeast on beer appearance and flavour as discussed above, information is scarce on the impact of bacteria on beer appearance and flavour. Bacteria mainly cause turbidity, sediments, acidification, off-flavour formation and ropiness (Sakamoto Konings, 2003 Suzuki, 2011 Suzuki et al., 2008). Suzuki (2011) and Vriesekoop, Krahl, Hucker, and Menz (2012) recently sununarised the positive and negative influences of bacteria on flavour and off-flavour in recent reviews, which form the basis of this section. Interested readers are referred to these articles for further details. 

More recent studies have demonstrated that the removal of nutrients by yeast does not always explain the observed inhibition of O. oeni. For instance, Larsen et al. (2003) reported that the addition of supplemental nutrients to a wine fermented by S. cerevisiae strain V1116 did not relieve the observed bacterial inhibition. Studying the impact of yeast autolysis on MLF, Patynowski et al. (2002) also concluded that nutrient depletion by S. cerevisiae was not responsible for the observed bacterial inhibition. Furthermore, this research showed that the yeast produced an unidentified inhibitory factor(s) that was progressively lost during aging. These results suggested that the second proposed theory, the production of toxic metabolites by yeast, may be responsible for the inhibition of O. oeni. 

Erasmus, D.J., M. Cliff, and H.J.J. van Vuuren. 2004. Impact of yeast strain on the production of acetic acid, glycerol, and the sensory attributes of icewine. Am.J. Enol. Vitic. 55 371-378. 

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