Yeast metabolism and beer flavour

Question 1

what does the first tier of the flavour wheel cover

Answer 1

14 classes
-4 taste
-8 aroma
-mouthfeel
-fullness

Question 2

what flavours do hops add to beer

Answer 2

bitterness
aroma compounds

Question 3

what flavours does malt add to beer

Answer 3

sweetness
body
aroma compounds
polyphenols

Question 4

what flavours does water add to beer

Answer 4

salts
buffering
modulate flavour perception

Question 5

what flavours does yeast add to beer

Answer 5

ethanol
CO2
aroma compounds
organic acids

Question 6

7 flavour compounds generated during fermentation

Answer 6

acetylalderhydes
organic acids
higher alcohols
esters
phenols
diactyls
sulfur compounds

Question 7

examples of organic acids

Answer 7

succinate
lactate
acetate

Question 8

what do organic acids contribute to flavour

Answer 8

sour/acid flavour

Question 9

how do acetaldehydes form

Answer 9

autolysis of yeast during lagering
ethanol oxidation post femrentation

Question 10

what is the flavour od acetylaldehydes

Answer 10

green apple/solvent arooma

Question 11

how are higher/fusel alcohols formed

Answer 11

amino acid metabolism and protein synthesus

Question 12

what flavour characters do higher alcohols add

Answer 12

spiciness, alcoholic (wine-like), floral

Question 13

what is a precursor for flavour active esters

Answer 13

higher alcohols

Question 14

amyl alcohol (alcohlic, marzipan ) is formed form which amino acid

Answer 14

isoleucine

Question 15

isoamyl alcohol (alcoholic, fruity) is formed from which amino acid

Answer 15

leucine

Question 16

isobutanol (alcoholic, fruity) is formed from which amino acid

Answer 16

valine

Question 17

2-phenyl ethanol (floral, rose) is formed from which amino acids

Answer 17

phenylalanine

Question 18

what flavour characters do esters add to beer

Answer 18

fruity
solvent like in excessive levels

Question 19

how are esters formed

Answer 19

by-products of sugar and lipid metabolism
-condensation reaction between alcohol + activated acyl coA

Question 20

what are the reactants to form an ester through CHO metabolism

Answer 20

CHO metabolism (from pyruvate) + acetyl CoA

Question 21

what are the reactants to form an ester through lipid metabolism

Answer 21

fatty acyl CoA + lipid metabolism

Question 22

two types of esters

Answer 22

acetate esters
fatty acid ethyl esters

Question 23

how are phenols produced

Answer 23

specialty yeast strains

Question 24

what beers use the specialty yeast strains that produce phenols

Answer 24

german wheat beer
Belgian specialty beer

Question 25

how else can phenols become present in beer

Answer 25

contamination of wild yeast or bacteria

Question 26

what compounds are collectively known as the vicinal diketones (VDK)

Answer 26

diactyl
2,3-pentandione

Question 27

what flavour character does diacetyl have

Answer 27

buttery, butterscotch flavour of beer
-rancid at high conc

Question 28

how are diacetyls formed

Answer 28

extracellular oxidative decarboxylation

Question 29

what is pentanedione

Answer 29

flavour compound similar to diacetyl
-mild honey butter flavour

Question 30

how is the concentration of diacetyls determined

Answer 30

synthesis of alpha-acetolactate

Question 31

what is apha-acetolactate

Answer 31

precusor for diacetyls forms by yeast and is excreted into wort

Question 32

factors increasing diacetyl

Answer 32

premature removal of yeast
overly flocculant yeast
low FAN
yeast strain
high fermentation temperture
poor yeast health
low O2 during pitching
bacterial infection

Question 33

prevention of diactyl

Answer 33

yeast strain
appropriate fermentation temp
good sanitation
increased temp at end of fermentation to facilitate conversion of acetolactate to diacetyl
healthy yeast
sufficient yeast
avoid O2 after fermentation

Question 34

anaeroboic yeast metabolism

Answer 34

glucose-> pyruvate-> acetylaldehyde->ethanol

Question 35

when is CO2 produced in yeast metabolism

Answer 35

during the conversion of pyruvate to acetaldehyde