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Maintaining Ideal Yeast Health:Nutrients Yeast Need
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What makes a great beer?
Fermentation. You put the yeast in, and then thefermentation takes about a week. A lot happens in that
week. The trick is to give the yeast exactly what it
wants. Its a mould and it wants to eat, and while it
eats, it makes alcohol and gas.
Interview with Eric Molson; Globe and Mail, May 29, 2009
Eric Molson
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General concept
Wort
nutrients
Yeast
Beer
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Importance of Yeast toBeer Characteristics
Around 950 compounds arethought to give beer its character
Of these, around 400 are producedby yeast!
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WORT(sugars, amino acids, etc.)
Acids (organic & fatty)
Alcohols (ethanol
& fusel oils)
Glycerol
Esters
Aldehydes & ketones
Sulphur compounds
Phenols
Yeast autolytic
compounds
CO2
More yeast!
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Elemental requirements for
growth of brewing yeast
H - cell water, organic materialO - respiration, cell water, organics
C - organic material
N -proteins, nucleic acids, coenzymes
S -proteins, coenzymes
P - nucleic acids, phosphoslipids
K - cell electrolyte, enzyme cofactor
Mg - enzyme cofactor, cell division
Ca - flocculationMn - enzyme cofactor
Fe - cytochromes
Zn - alcohol dehydrogenase
Co - vitamin B12, coenzymes
Cu, Ni, Mo - specialisedenzymes
Macroelements Microelements
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Yeast nutrients in wort Carbohydrates (fermentable sugars) Nitrogen sources (mainly amino acids)
Inorganic sources (P, S, Mg, Zn, other minerals)
Oxygen (need around 25% saturation of wort)
Yeast foods(vitamins, fatty acids, sterols)
NOTE: The level and availability of such nutrients is very
important in governing fermentation performance of brewingyeast
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Wort composition influences:
Rate of attenuation Degree of attenuation
Amount of yeast produced
Flocculation
Beer characteristics
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Carbon sources for brewingyeast Hexose sugars: glucose, fructose
Pentose sugars: no (but possibly xylulose)
Disaccharides: maltose, sucrose, melibiose
Trisaccahrides: maltotriose (slowly) Tetrasaccharides: maltotetraose (possibly some strains)
Oligosaccharides: maltodextrins (unfermented)
Polysaccharides: starch (unfermented)
Others: ethanol, acetate, glycerol (only respired)
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Nitrogen sources forbrewing yeast
Peptides Amino acids
Ammonium salts (little present inwort)
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Inorganic sources forbrewing yeasts
Phosphorus, sulphur and potassium generally
sufficient in wort
Metal cations may occasionally be deficient (andratios of metal ions may be sub-optimal)
Essential bulk ions: K, Mg
Essential trace ions: Zn, Ca, Fe, Mn
Toxic trace ions: Pb, Cd, Cr, Hg, Cu etc.
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Zinc Faster fermentation
Better flocculation
Stimulates uptake of maltose and maltotriose
Stimulation of protein synthesis and yeastgrowth
Protection of enzymes
Stabilisation of protein and membrane system
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Zinc Concentration in Wort
During wort preparation approx. 95 % of zincfrom malt are lost with spent grain
In modern stainless steel breweries the zinc
concentration is not sufficient (
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Zinc wort content is almostzero after 1 hour
Zn is entirely accumulated intocells which redistribute the metalamong growing yeast
LAGER strain-25C
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12 14 16 18 20 22 24
Time (h)
Zncellassociated(fg/cell)
0
0.06
0.12
0.18
0.24
0.3
0.36
0.42
0.48
0.54
0.6
Znsupernata
nt(ppml)
Cell Supernatant
LAGER strain-25C
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7
Time (h)
PercentageZncellassociated(%
)
Lager brewingyeast strain labconditions
G. Walker, ASBC 2007, Victoria, Canada
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Zn & fermentation performanceZn & fermentation performance
Low zinc (0.05 ppm)Low zinc (0.05 ppm)delaydelayeded sugar utilizationsugar utilization
High zinc (10 ppm) slightlyHigh zinc (10 ppm) slightly
delaydelayeded sugar utilizationsugar utilization
but same after 14 daysbut same after 14 days
fermentationfermentation
0.4 ppm0.4 ppm--1.0 ppm Zn1.0 ppm Zn
resultresulteded in fastestin fastestfermentation ratesfermentation rates
1.000
1.010
1.020
1.030
1.040
1.050
1.060
0 48 96 144 192 264
Time (hours)
Specificgravity
0 0.05 0.12 0.48 1.07 10.8 (Zn ppm)
0
1
2
3
4
5
6
7
48 96 144 192 264Time (hours)
Ethanol(%)
0 0.05 0.12 0.48 1.07 10.83 (Zn ppm)
Specific gravitySpecific gravity
EthanolEthanol
G. Walker, ASBC 2007, Victoria, Canada
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Vitamin sources forbrewing yeasts
Wort generally sufficient in folic acid,thiamine, riboflavin, pantothenic acid,niacin, inositol and biotin
Biotin, however, may occasionally bedeficient
Can supplement wort with yeast foods
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Typical levels of vitamins
in wortVITAMIN LEVEL IN
WORT /100mlMETABOLICROLES
Biotin 0.5g Carboxylations
Thiamin (B1) 60g Decarboxylations
Pantothenate (B5) ~50g Acetylations, CoA
Nicotinic acid (B3) 1000g Coenzymes
Riboflavin (B2) 50g Coenzymes
Pyridoxine (B6) 85g Amino acidmetabolism
Inositol 10mg Membranes
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Yeast transport strategies for
wort nutrients
WORT
NUTRIENTS
?
YEASTMETABOLITES
(beer)
?
Yeastcell
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Translocation of wortnutrients into brewing yeast
CELLULAR BARRIERScapsule, cell wall, periplasm, plasma membrane,
organelles
PHYSICO-CHEMICAL BARRIERS
chelation, adsorption, molecular size, binding
(e.g. nutrient unavailability in wort particles)
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PHYSICO-CHEMICAL
BARRIERS Zinc chelates with phytic acid, proteins &
polyphenols
These complex compounds are very stable
Only ionic zinc is available to yeast
Regular AAS is a destructive method, whichmeasures total zinc not available zinc
Ion-exchange separation separates complexand ionic zinc before AAS
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Derived from: Vecseri-Hegyes, B., P. Fodor, et al. (2005). "The Role of Zinc in Beer Production, I(Wort Production)." Acta Alimentaria 34(4): 373-380.
Total and complex zinc concentration of industrial wort samples
0
0.02
0.04
0.06
0.08
0.1
0.12
1 2 3 4 5 6
zincco
ncentration[mg/L]
total zinc
complex zinc
available zinc
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Consequences of low
assimilable nitrogen wort
Low available nitrogen, especially in
very high gravity wort, below athreshold of around 150mg/L, may
lead to stuck fermentations
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Amino acid uptake by brewing
yeast
GROUP A (fast)
Glu, Asp, Asn, Gln,
Ser, Thre, Lys, Arg
GROUP C (slow)
Gly, Phe, Tyr, Try,
Ala, NH3
GROUP B (intermediate)Val, Met, Leu, Isoleu, His
GROUP D (little or no)
Pro
NOTE: A variety of transport permeases
exist for (active) amino acid uptake by brewing yeast
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Yeast growth vs. Diacetyl Levels
Synthesis of valine/leucine required
acetolactate produced
0
5
10
15
20
25
30
0 1 2 3 4 5 6 7
Days Fermentation
Yeast
Growth
0
0.1
0.2
0.3
0.4
0.5
0.6
0.70.8
0.9
1
Dia
cetyl
Degrees Plato
Yeast growth g/L
Diacetyl (mg/L)
Valine/Isoleucine synthesis required
-acetolactate produced
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Mechanisms for yeast food enhanced
reduction of diacetyl levels?
- acetolactate diacetyl
By-product of valine
and isoleucine synthesis
by yeast
acetoin
Oxidative
Decarboxylation
(Slow)
Yeast reductase - fast
Requires functioning cell membrane
to allow for uptake of diacetyl prior
to reduction
Amino acids supplied by yeast foodsMay reduce requirement for synthesis
of valine/isoleucine (and thus - acetolactate
and diacetyl production)?
Provision of usable nitrogen sourceplus other nutrients results in a more
vital cell that is enhancing diacetyl
uptake and reduction?
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Yeast nutritionpotential problems for fermentation
Spectrum/availability of wort sugars
e.g. High glucose worts may slow fermentation
Insufficient FAN
Stuck fermentation, change in flavour profile
Metal ion availabitiy e.g. Low Zn, excess Ca, insufficient Mg, toxic Cu
Vitamin deficiency(e.g. pantothenate - sulphur off-notes)
Stressed yeast - impaired nutrient uptake(ethanol, pH, CO2, temp., starvation, osmotic pressure.)
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Yeast Foods
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Commercial Yeast Foods
Available Components Amino acids (FAN)- as protein hydrolysate or added as
individual amino acids
Low molecular weight peptides
NH4+
Growth factors (vitamins)
Protein (non-utilisable) active in CO2 nucleation? Sulphur/Phosphorous
Zn/Cu/Mn/Ca (enzymatic and structural roles)
Yeast hulls (broken cell walls) as sterol/FA source,nucleation site
Ergesterol expensive
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Typical Yeast Food Effects* Improved alcohol yield (increased extract
utilization)
Reduction in fermentation time (12-24h)
Enhanced yeast vitality Protect against stress
Enhanced diacetyl removal/consistent diacetylspecification
Control of undesirable flavour compounds
* Depending on the yeast food composition
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Nutrient Trial ResultsEastern European Brewery A
6.86.3
71
98
34.9 33.2
0
10
20
30
40
50
60
70
80
90
100
Primary Fermentation
Time (days)
VDK in specification at
time (%)
Average Diacetyl (ppb)
Control
Nutrient
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Nutrient Trial ResultsEastern European Brewery B
4 6
148
87
3.7 3.3
0
20
40
60
80
100
120
140
160
Primary Fermentation Rate
(degP/Day)
Final Diacetyl Level (ppb) Residual Extract
Control
Nutrient
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Servomyces
Weihenstephan Trials15L lab trials Sample 1: no zinc addition (O-wort)
Sample 2: addition of 0.3 mg/L ZnCl2
Sample 3: addition of 8 mg/L inactive yeast
Sample 4: addition of 8 mg/L SERVOMYCES
Sample 5: addition of 2.3 mg/L SERVOMYCES
Sample 6: addition of 8 mg/L inactive yeast + 0.3 mg/L ZnCl2 Initial yeast zinc pool: 4.1 mg/100 g
3.115.1311.612.634.152.67Crop yeast
[mg/100 g]
0.340.361.220.110.350.10Initial wort
[mg/L]
inactive yeast
+ ZnCl2
SERVOMYCES
Low Addition
SERVOMYCES
High Addition
inactive
yeastZnCl20-wort
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ServomycesWeihenstephan Trials
Fermentation in 15L CCT at 10 C
2
4
6
8
10
12
14
0 1 2 3 4 5 6 7 8 9
fermentation days
Extract[
Plato]
ZnCl
inactive yeast
Servomyces - high addition
0-Wort
Servomyces - low addition
inactive Yeast + Zn Cl
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Servomyces Trial ResultsUS Brewery
4
5
6
7
8
9
10
11
12
13
14
0 1 2 3 4 5 6
Fermentation days
Extract[B
rix]
Servo addition A Servo addition B
No Servo A No Servo B
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Propagation With each cell division the internal zinc pool is
divided between mother and daughter cell
Fermentation 4-5 times biomass increase
Propagation 15-20 times biomass increase
=> very low internal zinc pool
Slower, less efficient propagation
Fermentation problems in 1. generation beer
Slower, stuck fermentation Longer diacetyl rest
Less flocculent yeast
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The Impact of Nutrients on
High Gravity/Adjunct Brew
60% malt / 40% adjunct / 18P / Gen 1
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
0 1 2 3 4 5
time [day]
Extract[%w
/w
]
Control A F
B D C
E
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Serial Repitching Repeated stress for the yeast
Decline in yeast activity
Resistance to stress is strain
dependent
Contamination
Genetic drift/petite mutation
The Impact of Yeast Generation on the
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The Impact of Yeast Generation on the
Use of NutrientsHigh Gravity/Adjunct Brew
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
0 1 2 3 4 5
time [day]
Extract[%
w/w]
Control A F
B D C
E
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
0 1 2 3 4 5 6 7 8 9
time [day]
Extract[%
w/w]
Control A F
B D C
E
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
time [day]
Extract[%
w/w
]
Control A F
B D C
E
Gen 1 Gen 6
Gen 8
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Nucleation SitesEffect of dissolved CO2
Inhibits growth and metabolism
Decreases multiplication rate
Reduces biomass yield
Increases lag phase
Inhibition of nutrient uptake
Loss of cell division and bud formation
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Nucleation Sites Particles working as nucleation sites reduce the
solubility of CO2
Most nucleation in a fermenter occurred fromparticles that sedimented to its bottom
Particle size is a likely determinant of theparticles ability to be an effective CO2 nucleator
The more porous a particle is, the most efficient itis as a nucleation site
Soy flour may be ruled out due to allergen issues
N l i Si D i
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Nucleation Sites Degassing
Activityreleased CO2after 2.5 hours
Control Soy Flour A B C0
1
2
3
4
CO2[g/L
]
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