10 Flashcards
(15 cards)
How does yeast contribute to beer flavor?
Yeast contributes significantly, with many potentially flavor-active compounds arising during fermentation as from raw materials.
What is the estimated number of flavor and aroma components produced by yeast in beer?
Around 1000 flavor and aroma components are estimated to be produced by yeast.
How do different yeast strains impact beer flavors?
Different strains produce different spectra of flavor compounds, with strain-specific differences reflecting subtle genetic variations.
From which metabolic pathway are key flavor-active yeast metabolites derived?
Flavor-active compounds can be derived from the pyruvate metabolic pathway, including carbon dioxide, ethanol, glycerol, and others.
How is ethanol produced during fermentation?
Ethanol is formed by converting glucose to pyruvate, which is then converted to acetaldehyde and reduced to ethanol, a process that also generates ATP.
What are higher alcohols and how are they formed?
Higher alcohols are byproducts of amino acid synthesis or breakdown and are involved in controlling the redox state and possibly intracellular pH.
What triggers chain formation in brewing yeasts?
Chain formation may be due to a disruption in the chitinase gene, important for breaking down chitin at the bud/birth scar, and is hereditary.
How does flocculation occur in brewing yeasts?
Flocculation is a reversible aggregation of cells causing them to sink or rise in the medium, influenced by environmental conditions and is critical in industrial fermentations.
What is the significance of flocculation in brewing?
Flocculation is crucial for efficient sugar utilization during active fermentation and for yeast separation from green beer after fermentation.
How is flocculation traditionally classified in brewing yeasts?
Historically, lager strains were bottom fermenting and ale strains top fermenting, with four classes ranging from non-flocculent to intensely flocculent.
What modern classifications exist for yeast flocculation based on sensitivity to sugars?
Strains can be classified as Flo1 phenotype (inhibited by mannose) and NewFlo phenotype (inhibited by mannose, glucose, and maltose), with most brewing strains showing the NewFlo phenotype.
Describe the role of the yeast cell wall in flocculation.
The cell wall’s structure, which retains flocculation capacity even in heat-killed cells, plays a crucial role in flocculation.
How do yeast cells interact to facilitate flocculation?
Flocculation involves calcium-mediated activation of flocculins on yeast cell surfaces, with sugar molecules in the wort binding to flocculins and preventing attachment, allowing deflocculation.
What external factors can promote or inhibit yeast flocculation?
Calcium and mild agitation promote flocculation, while high salt concentrations, very low pH, and certain cell surface properties inhibit it.
How do internal and external factors influence the flocculation process in yeast?
Genetic factors, such as the presence and expression of FLO genes, and environmental conditions like sugar availability and ion concentration, govern flocculation.
