9 Flashcards
(16 cards)
How does yeast contribute to beer flavor?
Yeast is a major player in flavor production, contributing as many potentially flavor-active compounds during fermentation as those derived from raw materials.
Estimate the number of flavor and aroma components produced by yeast in beer.
It is estimated that there are around 1000 flavor and aroma components in beer, mostly produced by yeast.
How do different yeast strains affect beer flavor?
Different yeast strains produce different spectra of flavor compounds, affecting the beer’s overall taste subtly but significantly.
What are the key flavor-active yeast metabolites derived from pyruvate?
Flavor-active compounds from pyruvate include carbon dioxide, ethanol, glycerol, organic acids, aldehydes, ketones, higher alcohols, short chain fatty acids, esters, and sulfur compounds.
How is ethanol formed during yeast fermentation?
During fermentation, glucose is converted into pyruvate, which is then transformed into acetaldehyde and reduced to ethanol, generating energy (ATP) and maintaining NADH/NAD balance.
What are higher alcohols, and how are they formed?
Higher alcohols are products of amino acid synthesis or breakdown, involved in redox control and possibly intracellular pH adjustment.
Describe the process and significance of amino acid uptake in yeast.
Amino acids are transported into the cell via specific and general permeases, used directly for protein synthesis or deaminated for other metabolic functions.
What is nitrogen catabolite repression in yeast?
Readily assimilable nitrogen sources suppress the genes responsible for the uptake and catabolism of less readily available nitrogen sources, affecting amino acid uptake.
How are esters formed in yeast, and what role do they play?
Esters are formed by tuning fatty acid and energy metabolism, consuming acetyl-CoA to regenerate CoA, and facilitating the diffusion of toxic medium chain fatty acids out of the cell.
What is the role of acetaldehyde in yeast metabolism and flavor production?
Acetaldehyde is an immediate precursor to ethanol; it accumulates if it cannot be reduced, influencing flavor.
How are volatile diacetyl compounds (VDK) formed in yeast?
VDK like diacetyl are derived from intermediates in amino acid synthesis and can impact beer flavor if not managed properly during fermentation.
How do organic acids contribute to beer flavor?
Organic acids are intermediates in energy metabolism, excreted during yeast growth, contributing to the beer’s pH and flavor profile.
How does substrate composition and fermentation conditions affect yeast?
Yeast perceives substrates as complex mediums, influencing nutrient uptake, metabolic performance, and flavor compound production based on sugar, nitrogen source, and nutrient availability.
What are the consequences of environmental conditions like oxygen on yeast during fermentation?
Elevated oxygen levels favor increased yeast growth, influencing substrate availability for flavor compound formation and impacting ester synthesis through gene regulation.
How do genomic and phenotypic factors affect yeast’s flavor-producing capabilities?
The yeast genome and external conditions dictate the potential and actual flavor production, with minor variations in key metabolic genes influencing strain-dependent flavor profiles.
How do physical conditions influence the flavor compounds produced by yeast?
Physical factors such as cell membrane properties and fermentation conditions affect how flavor compounds are retained or released by yeast, with variations observed between different yeast strains and fermentation temperatures.
