Fermentation, maturation, clarification carbonation Flashcards
(29 cards)
why must the wort be aerated during transport to fermentation vessels
yeast needs oxygen to synthesize unsaturated fatty acids and sterols for cell membranes
where is yeast grown and how is it added to the wort
grown in a propagation vessel, then ‘pitched’ and added to the wort for fermentation
why must yeast be healthy
viable: able to grow
vital: able to ferment
prevent off-flavours
rule of thumb for how much yeast should be added
1 mill cells per ml per degree plato
metabolic/ respiration behavior of yeast
facultative aerobes
how is glucose femneted by yeast
glycolysis produces pyruvate which gets decarboxylated into 2-acetylaldehyde which is reduced using NADH as an electron transporter into ethanol
changes in wort during fermentation
specfic gravity increases as the sugars are turned into alc
yeast numbers grown
pH decreases
FAN decreases
flavour compounds are produced
-esters
-higher alcohols
-others
what happens during ale fermentation
top fermenting
-yeast rises to the top and create a thick yeasty head
-warmer 15-20C
-rapid growth
-more fruity esters
what happens during lager fermenting
bottom-fermenting
-colder temp 6-15C
-slow growth
-longer fermentation/maturationn
-less fruity, more sulphury aroma
during lager fermentation what happens to the temp after primary fermentation
dropped by 1-1.5C
why are less fruity esters/by-products produced during lager fermentation
the low temperature retard their development
what happens once the yeast complete fermentation
flocculation
if not enough yeast is removed after flocculation/maturation what can happen to the beer
the yeast can generate off-flavours due to lysing
how is the yeast harvested
skimming/’top cropping’
collection from a cone at the bottom of the vessel
what happens to the yeast that is removed
disposed of
used for another fermentation
what is the beer referred to as right after the yeast has been removed?
green beer
what happens to the green beer before the sale
matured/conditioned
at what temperature does conditioning/lagering occur?
-1-4C
what is the purpose of lagering/conditioning
refine flavour profile
remaining yeast settles out
protein precipitation to improve clarity
when does clarification occur
at least 3 days after cold conditioning
how is beer clarified
centrifugation
filtration
what filtration methods are commonly used
membrane filtration
kieselguhr/diatomaceous earth (porous particles)
what is the purpose of stabilisation
remove microorganisms
two types of stabilisation
pasteurisation
flash pasteurisation
