Download Yeast Nutrition and Fermentation Progression

Yeast Nutrition and
Fermentation Progression
Linda F. Bisson
Department of Viticulture and Enology
Issues in Fermentation Management,
2011
Outline of Presentation
General introduction to nutritional needs
during fermentation
 Special considerations

– Native fermentations
– Vineyard factors impacting nutrition
– Winery production factors impacting nutrition
GENERAL INTRODUCTION
Yeast Need Nutrients To:
Build new cells
 Make and modify metabolic pathways
 Repair and prevent cell damage
 Adapt to changing environments

Yeast Nutritional Phases
stationary
Cell
#
death
log
Brix
lag
Time
BUILDING NEW CELLS
Yeast Nutritional Phases: Building New
Cells
stationary
Cell
#
death
log
Brix
lag
Time
Yeast Nutrition: Building New Cells
Energy source: Ability to capture and
reuse bond energy
 Macronutrients: Building blocks needed
for new cell material
 Micronutrients: Catalysts needed to
facilitate biochemical reactions related to
growth

Yeast Nutrition: Building New Cells
Energy source: labor
 Macronutrients: bricks and mortar
 Micronutrients: equipment

Macronutrients
Carbon/Energy Sources: glucose,
fructose, sucrose
 Nitrogen Sources: amino acids,
ammonia, nucleotide bases, peptides
 Phosphate Sources: inorganic
phosphate, organic phosphate
compounds
 Sulfur Sources: inorganic sulfate,
organic sulfur compounds

Growth Macronutrients in Juice
Carbon: Excess
 Nitrogen: Excess to Deficiency
 Phosphate: Sufficient to Deficiency
 Sulfate: Sufficient

Carbon Sources
For carbon component: role in new cell
material (bricks and mortar)
 To be degraded to recapture bond energy:
role as energy source to perform needed
metabolic reactions (labor)

Yeast Carbon/Energy Sources
in Juice:
Monosaccharides: glucose, fructose,
galactose, mannose
 Disaccharides: sucrose, maltose,
melibiose
 Trisaccharides: raffinose
 Pentoses: Not used

Yeast Carbon (NOT Energy)
Sources in Juice:
Metabolic Intermediates: TCA cycle acids:
malate, fumarate, succinate, oxalacetic
acid, citrate
 Oxidative substrates: pyruvate, acetate,
lactate, glycerol, ethanol
 See dynamic changes in concentrations in
juice during fermentation, role in
metabolism and growth not clear

Nitrogen Sources
For Saccharomyces, function exclusively in
building new cells and new pathways
 Bacteria and some non-Saccharomyces
yeasts can use nitrogen compounds as
energy sources
 Nitrogen most often the limiting factor in
the Saccharomyces environment

Yeast Nitrogen Sources
Ammonia
 Most amino acids
 Degradation may depend upon availability
of other components: vitamins and oxygen
 Utilization impacted by other
environmental factors such as pH and
ethanol

Categories of Yeast Amino Acid
Nitrogen Sources
Compound may be used as that amino
acid for biosynthesis
 Compound may be converted to related
amino acids for biosynthesis
 Compound may be degraded with release
of nitrogen (be mindful of potential end
products!)

Phosphate Sources
Inorganic phosphate
 Organic phosphate-containing molecules
under starvation conditions only
 Prefer to make their own

– Internally generated phosphate-containing
molecules perform important regulatory roles
– If taken in from outside might send false
signal

Roles as building blocks and in energy
movements
Sulfate Sources
Sulfate
 S-containing amino acids
 Used for building new cell material
 Used in formation of catalysts

Micronutrients for Building New
Cells
Minerals and Trace Elements: Mg, Ca,
Mn, K, Zn, Fe, Cu
 Vitamins: biotin is the only required
vitamin, but others are stimulatory
 Generally depending upon how the cells
are grown previously micronutrients are
not limiting

MAKING AND MODIFYING
METABOLIC PATHWAYS
Yeast Nutritional Phases: Modifying
Pathways
stationary
Cell
#
death
log
Brix
lag
Time
Making and Modifying Pathways
Needs energy for degradation and
reconstruction
 May need influx of net new nutrients if
requirements not readily met by
degradation (mostly a nitrogen issue)
 Requires micronutrients for generating the
new pathway and for operating the
enzymes of that pathway

Making and Modifying Pathways
Happens during active growth
 Happens under non-proliferative but
metabolically active growth conditions:
sustaining fermentative capacity

Most of the fermentation is
conducted by “stationary” phase cells
Stationary phase means no net increase in
viable cells:
1. rate of growth = rate of death
2. quiescent = no growth, no death
Making and Modifying Pathways
How uniform is the culture?
 Are there distinct metabolic sub-populations
of cells?

Making and Modifying Pathways
How uniform is the culture?
ANSWER: It depends, but highly likely to
not be uniform
 Are there distinct metabolic sub-populations
of cells?
ANSWER: YES
 Goal of fermentation management: keeping
cells optimally active

Keeping Cells Metabolically
Active
Feeding enough at the appropriate time so
they have what they need
 Being mindful of factors that alter
nutritional needs:

– Demand new pathways (have to do
something different)
– Impose metabolic stress (have to do it in a
different way)

Understanding the needs of the strains
being used (commercial or native)
REPAIRING AND PREVENTING
CELL DAMAGE
Yeast Nutritional Phases: Repair and
Prevention of Damage
stationary
Cell
#
death
log
Brix
lag
Time
Repairing and Preventing
Damage
Adaptation to ethanol
 Addressing presence of stressors in
fermentation
 Requires “survival factors”
 Mother Nature selects for surviving rather
than completing your fermentation

Role of Survival Factors
 Maintain
viability of cells
 Increase ethanol tolerance
 Maintain energy generation
Survival Factors
Oxygen
 Fatty Acids
 Sterols
 Nutritional Factors

Survival Factors
Needed to alter composition of the plasma
membrane (sterols, fatty acids and
proteins) so that it can withstand the
perturbing effects of ethanol
Both phospholipid and protein content must
be adjusted
ADAPTATION TO CHANGING
ENVIRONMENTS
Yeast Nutritional Phases: Adaptation
stationary
Cell
#
death
log
Brix
lag
Time
The Need to Adapt
Can happen at any time
 Temperature shift
 Introduction or bloom of other organisms
 Change in chemical environment (pH,
sugar content, ethanol content)

The Need to Adapt
May exceed internal capacity of nutrient
recycling
 If need new nutrients their choice is
continue to be active or use those
nutrients to enter a stable dormant phase
 If stress is too severe they might not be
able to readjust and adapt
 Again, Mother Nature selects for survival
not completion of your fermentation

Outline of Presentation
General introduction to nutritional needs
during fermentation
 Special considerations

– Native fermentations
– Vineyard factors impacting nutrition
– Winery production factors impacting nutrition
Native Fermentations
Nutritional requirements of cells present
not known
 More typically than not, a mixed
population of Saccharomyces and non
Saccharomyces
 Saccharomyces population is not going to
be uniform
Mixed Populations
More competition for nutrients
 Accumulation of inhibitory end products
 Non-homogeneity of Saccharomyces

– In some regions this leads to domination by
less fermentatively robust strains = strong
initiators are not a priori strong finishers
Heterogeneity

The Good News:
– Greater complexity
– Selection for survivalists
– Slower fermentations

The Bad News:
– Higher risk of something going wrong
– Need to pay closer attention than with
commercial inoculants
Viticultural Factors Impacting
Nutrition
First source of nutrients
 Can be a source of inhibition
 Rot changes fermentation dynamics
 Sometimes need to get yeast nutrition
right in the vineyard, winery additions do
not seem to compensate

Winery Production Factors
Impacting Nutrition

Manipulations of microbial populations
 Cold soaks
 Heat treatments
 Holding of fruit

Manipulation of fermentation environment




Temperature
pH adjustments
Aeration and mixing practices
Tank dimensions