Top fermenting yeast
Morphological characteristic
- Form chains of budded cells
- The mother & daughter cells remain attached to one another for a longer time & result branch chain of cells are formed
Physiological deference
- Can’t ferment trisaccharide raffinose
- Short fermentation because it’s produced respiratory metabolism
- Yeast crop after fermentation is much greater
- Have a higher enzyme content
- Spore formation takes longer
Fermentation technological differences
- Yeast rise to the surface during fermentation
- Yeast can’t form flocs
- produce a turbid beer with a higher degree of attenuation
- Fermentation temperature are performed between 14 oC to 25 oC
Bottom fermenting yeast
Morphological characteristic
- Occur almost as single cell or pair of cells
- Mother & daughter cells separate from one another
Physiological deferences
- Can ferment trisaccharide raffinose because of their enzyme spectrum use raffinose completely
- Long fermentation because metabolism dominates by far
- Low yeast crop after fermentation
- Have a lower enzyme content
- The ability to form ascospore is limitted
Fermentation technological differences
- Yeast settle to the bottom at the end of fermentation
- Flocculation behaviour which the cells clump together after a short time to form large flocs & the settle rapidly
- In the case of powdery yeasts the cells remain very finely divided in the fermentation medium & sink slowly to the bottom only at the end of fermentation
- Flocculant yeast produce a clear, but less fully fermented beer
- Powdery yeasts produce a turbid beer with a higher degree of attenuation
- Fermentation temperature are performed between 4 oC to 12 oC
Tuesday, February 14, 2012
How yeast multiplication?
Yeast multiplication & growth
- Yeasts normally reproduces by budding
- During budding a small bubble from the mother cell is formed which a part of the cytoplasm as well as a daughter nucleus
- In some yeast strains the mother & daughter cells separate from one another completely
- In other strains the cells remain connected to one another & form chains log cell number
- The growth is divided into six phase;
1. Lag phase
- Is an activation of metabolism
- The length of phase depends on type of organism & condition
- The length of phase varies greatly
2. Acceleration phase
- The rate of division continuously increases
3. Exponential phase (logarithmic growth or log phase)
- The growth rate is constant & maximal, which the cell number doubles
- The time period is minimal , it’s about 90-120 min
4. Deceleration phase
- Because of reduction in the amount of nutrient substrate or an increase in the amount of inhibiting metabolic products
- The growth rate is decreased
5. Stationary phase
- The number of microorganisms remain constant
- There is balance between the number of newly formed cells & the cells which die
6. Declining phase
- The rate of cell death exceeds the rate of new cell formation
- The cell number therefore decreases
The duration & size of the growth phases are influenced by;
1.Water
- Is the main component of living material & important in the life process
- Microorganism are only able to develop in substrates which contain at least 15% water content
2. pH
- Yeast growth preferably at acidic pH
- Microorganism differ from one another with their optimal pH
3. Temperature
- Every microorganism has its optimum temperature
- Yeast genus Saccharomyces this is usually temperature between 0 oC & 40 oC
- The optimum growth temperature being about 25-30 oC
4. Oxygen
- Important for yeast growth
5. Nutrient
- The substrate must contain all the nutrients required for growth
- Yeasts normally reproduces by budding
- During budding a small bubble from the mother cell is formed which a part of the cytoplasm as well as a daughter nucleus
- In some yeast strains the mother & daughter cells separate from one another completely
- In other strains the cells remain connected to one another & form chains log cell number
- The growth is divided into six phase;
1. Lag phase
- Is an activation of metabolism
- The length of phase depends on type of organism & condition
- The length of phase varies greatly
2. Acceleration phase
- The rate of division continuously increases
3. Exponential phase (logarithmic growth or log phase)
- The growth rate is constant & maximal, which the cell number doubles
- The time period is minimal , it’s about 90-120 min
4. Deceleration phase
- Because of reduction in the amount of nutrient substrate or an increase in the amount of inhibiting metabolic products
- The growth rate is decreased
5. Stationary phase
- The number of microorganisms remain constant
- There is balance between the number of newly formed cells & the cells which die
6. Declining phase
- The rate of cell death exceeds the rate of new cell formation
- The cell number therefore decreases
The duration & size of the growth phases are influenced by;
1.Water
- Is the main component of living material & important in the life process
- Microorganism are only able to develop in substrates which contain at least 15% water content
2. pH
- Yeast growth preferably at acidic pH
- Microorganism differ from one another with their optimal pH
3. Temperature
- Every microorganism has its optimum temperature
- Yeast genus Saccharomyces this is usually temperature between 0 oC & 40 oC
- The optimum growth temperature being about 25-30 oC
4. Oxygen
- Important for yeast growth
5. Nutrient
- The substrate must contain all the nutrients required for growth
Yeast Cell a Wonderful Microorganism (Lecture Version)
What's Yeast?
- Yeast are unicellar microorganisms with can obtain the energy in the aerobic or anaerobic
- Fungi species Saccharomyces ceriviseae are used
- Structure & composition of the yeast cell
- Yeast cell is oval to round with length of 8-10 micron & breadth of 5-7 micron
- Yeast cell can only be seen under a microscope consist
Yeast Cell Structure
Bud scar
Cell wall ; give the yeast cell its shape & stability (manan+glucan)
Plasma ; containing cytoplasm
Plasma membrane ; semipermeable membrane
Vacuole ; store metabolic products temporarily (phosphate)
Polymetaphosphate granule
Mitochondria ; provide energy for the cell during respiration
Lipid granule
Endoplasmic reticulum
Nuclear membrane
Nucleus;control the metabolism & contain the genetic information
Nucleolus
Yeast metabolism
- The purposes of metabolism are;
- To take in usable substance as food
- To produce the energy
- Yeast able to utilize these sugars;
- In the presence of oxygen (aerobic)
- Is called respiration
- Produces more energy
- When oxygen is excluded (anaerobic)
- Is called fermentation
- Produces less energy
- Energy production by respiration for fermentation result from numerous reaction by specific enzyme
- The enzymes of the respiration are located in the mitochondria
- The fermentation enzymes are mainly in the cytoplasm
- The yeast cell can only take up substance depend on enzyme spectrum
Carbohydrate metabolism
- Louis Pasteur discoverer : Fermentation that is life without oxygen
- Yeast is only organism which can change from respiration to fermentation
- Fermentable carbohydrates include;
- Monosaccharides ; glucose, fructose, manose, galactose
- Disaccharides ; maltose, sucrose
- Trisaccharides ; raffinose, maltose (not by all yeasts)
- Glycogen & trehalose are a small fraction of sugar as a chemical energy for use when external sugar is not available
- The most important chemical energy reserves are;
- ADP (adenosine diphosphate)
- ATP (adenosine triphosphate)
- Is important as an energy reserve & it’s essential for all life process
Nitrogen metabolism
- Yeast requires nitrogen to form its own cellular protein
- The main nitrogen sources are amino acids & lower peptides
- It can’t use inorganic nitrogen compounds other than ammonium salts
- Yeast can’t simply use the amino acids in wort directly but are absorbed in a particular sequence;
- Degradation, transformation & synthesis reaction
- These processes are also formation of fermentation byproducts such as;
- Higher alcohol(fusel oil), diketone, esters & organic acid
- Formation of metabolic products are depend on a temperature , pressure & pH
Metabolism of inorganic substances & growth factors
- The following cations & anions affect enzymic reactions;
1. Potassium
- Stimulates all enzymic reactions
- Important for energy metabolism
2. Sodium
- Activates enzymes
- Important in the transportation of substances through the cell membrane
3. Calcium
- Assists break formation
- Can be replaced by manganese
4. Magnesium
- Very important for reactions especially during fermentation
5. Copper
- Even a low concentration inhibits some enzymes
6. Iron
- Important for the enzymes involved respiration
- Increase cell budding
7. Manganese
- Stimulate cell reproduction & cell growth
- Can be replaced by iron
8. Zinc
- Increase protein synthesis
- Very important for fermentation
- Requirement is about 0.2 ppm
- Zinc deficiency lead to defective fermentation
9. Sulphate
- Necessary for yeast cell material synthesis
10. Phosphate
- Important for the formation of high energy substances
- Fermentation is not possible without phosphate
- Deficiency result in inadequate enzymic activity
11. Nitrate
- Is reduced by bacteria to nitrite which poisons yeast cell & is determental to fermentation
Energy metabolism of yeast
- Respiration;
C6H12O6 + 6O2 >>> 6H2O + 6CO2
- Fermentation;
C6H12O6 >>> C2H5OH + 2CO2
- Only part of energy is available to the organism, the remainder is converted into heat
During respiration of glucose the heat of reaction is;
deltaH = 2,824 kJ/mol = 15,570 kJ/kg
- Yeast respires at most 2% of the sugar in the initial fermentation phase since after that no more oxygen is available
- As a result reaction heat is produced by the yeast
- Heat production during fermentation assumed;
105.5 kJ/mol = 586.6 kJ/kg
- This means that during fermentation only about 3.7% of the amount of energy which would be produced by respiration is released for the yeast
- Yeast are unicellar microorganisms with can obtain the energy in the aerobic or anaerobic
- Fungi species Saccharomyces ceriviseae are used
- Structure & composition of the yeast cell
- Yeast cell is oval to round with length of 8-10 micron & breadth of 5-7 micron
- Yeast cell can only be seen under a microscope consist
Yeast Cell Structure
Bud scar
Cell wall ; give the yeast cell its shape & stability (manan+glucan)
Plasma ; containing cytoplasm
Plasma membrane ; semipermeable membrane
Vacuole ; store metabolic products temporarily (phosphate)
Polymetaphosphate granule
Mitochondria ; provide energy for the cell during respiration
Lipid granule
Endoplasmic reticulum
Nuclear membrane
Nucleus;control the metabolism & contain the genetic information
Nucleolus
Yeast metabolism
- The purposes of metabolism are;
- To take in usable substance as food
- To produce the energy
- Yeast able to utilize these sugars;
- In the presence of oxygen (aerobic)
- Is called respiration
- Produces more energy
- When oxygen is excluded (anaerobic)
- Is called fermentation
- Produces less energy
- Energy production by respiration for fermentation result from numerous reaction by specific enzyme
- The enzymes of the respiration are located in the mitochondria
- The fermentation enzymes are mainly in the cytoplasm
- The yeast cell can only take up substance depend on enzyme spectrum
Carbohydrate metabolism
- Louis Pasteur discoverer : Fermentation that is life without oxygen
- Yeast is only organism which can change from respiration to fermentation
- Fermentable carbohydrates include;
- Monosaccharides ; glucose, fructose, manose, galactose
- Disaccharides ; maltose, sucrose
- Trisaccharides ; raffinose, maltose (not by all yeasts)
- Glycogen & trehalose are a small fraction of sugar as a chemical energy for use when external sugar is not available
- The most important chemical energy reserves are;
- ADP (adenosine diphosphate)
- ATP (adenosine triphosphate)
- Is important as an energy reserve & it’s essential for all life process
Nitrogen metabolism
- Yeast requires nitrogen to form its own cellular protein
- The main nitrogen sources are amino acids & lower peptides
- It can’t use inorganic nitrogen compounds other than ammonium salts
- Yeast can’t simply use the amino acids in wort directly but are absorbed in a particular sequence;
- Degradation, transformation & synthesis reaction
- These processes are also formation of fermentation byproducts such as;
- Higher alcohol(fusel oil), diketone, esters & organic acid
- Formation of metabolic products are depend on a temperature , pressure & pH
Metabolism of inorganic substances & growth factors
- The following cations & anions affect enzymic reactions;
1. Potassium
- Stimulates all enzymic reactions
- Important for energy metabolism
2. Sodium
- Activates enzymes
- Important in the transportation of substances through the cell membrane
3. Calcium
- Assists break formation
- Can be replaced by manganese
4. Magnesium
- Very important for reactions especially during fermentation
5. Copper
- Even a low concentration inhibits some enzymes
6. Iron
- Important for the enzymes involved respiration
- Increase cell budding
7. Manganese
- Stimulate cell reproduction & cell growth
- Can be replaced by iron
8. Zinc
- Increase protein synthesis
- Very important for fermentation
- Requirement is about 0.2 ppm
- Zinc deficiency lead to defective fermentation
9. Sulphate
- Necessary for yeast cell material synthesis
10. Phosphate
- Important for the formation of high energy substances
- Fermentation is not possible without phosphate
- Deficiency result in inadequate enzymic activity
11. Nitrate
- Is reduced by bacteria to nitrite which poisons yeast cell & is determental to fermentation
Energy metabolism of yeast
- Respiration;
C6H12O6 + 6O2 >>> 6H2O + 6CO2
- Fermentation;
C6H12O6 >>> C2H5OH + 2CO2
- Only part of energy is available to the organism, the remainder is converted into heat
During respiration of glucose the heat of reaction is;
deltaH = 2,824 kJ/mol = 15,570 kJ/kg
- Yeast respires at most 2% of the sugar in the initial fermentation phase since after that no more oxygen is available
- As a result reaction heat is produced by the yeast
- Heat production during fermentation assumed;
105.5 kJ/mol = 586.6 kJ/kg
- This means that during fermentation only about 3.7% of the amount of energy which would be produced by respiration is released for the yeast
Monday, February 13, 2012
Yeast Breeding with Classical Methods
Aim
– To construct fast fermenting yeast strains with
good brewing performance for production of
palatable lager beer
– To construct yeast strains for new products with
divergent flavour profiles
Approach
– To hybridise different brewer’s yeast strains
Breeding Parameters
• Fast fermentation
• High attenuation
• Good sedimentation
• +/- Esters
• +/- Sulphur compounds
• More sulphite
• Less diacetyl
How Do We Breed Yeast?
• Get access to culture collections with
brewer’s yeasts of different origin
• Test strains in small scale
• Identify strains with interesting
characteristics
– To construct fast fermenting yeast strains with
good brewing performance for production of
palatable lager beer
– To construct yeast strains for new products with
divergent flavour profiles
Approach
– To hybridise different brewer’s yeast strains
Breeding Parameters
• Fast fermentation
• High attenuation
• Good sedimentation
• +/- Esters
• +/- Sulphur compounds
• More sulphite
• Less diacetyl
How Do We Breed Yeast?
• Get access to culture collections with
brewer’s yeasts of different origin
• Test strains in small scale
• Identify strains with interesting
characteristics
Vitality
Definition:
“Yeast Activity or Physiological Health”
Or “Potential To Endure Stress and Still Perform”
How Can We Measure Yeast Vitality?
1. Glycolytic Flux
• pH
2. Cellular Components
• Glycogen
• Sterols
• Trehalose
Acidification Power Test
• Based on capacity of yeast slurry to acidify
surrounding medium.
• acidification power test measures the reduction in
extra-cellular pH before and after glucose addition
• The "acidification power" test serves as an indicator of the
yeast cells physiological condition
“Yeast Activity or Physiological Health”
Or “Potential To Endure Stress and Still Perform”
How Can We Measure Yeast Vitality?
1. Glycolytic Flux
• pH
2. Cellular Components
• Glycogen
• Sterols
• Trehalose
Acidification Power Test
• Based on capacity of yeast slurry to acidify
surrounding medium.
• acidification power test measures the reduction in
extra-cellular pH before and after glucose addition
• The "acidification power" test serves as an indicator of the
yeast cells physiological condition
Viability
Definition:
“Capacity of a Cell to Exhibit Life Functions”
How Can We Measure Yeast Viability?
1. Cell Replication
2. “Vital” Stains
3. Specialised Methods
Methylene Blue the best method to check Viability of Yeast
Advantages
• Rapid
• Inexpensive
• Simple
Disadvantages
• Unreliable Below 90%
• Stains Buds and Not Mothers
• Variation in Dye Intensity - Subjective
“Capacity of a Cell to Exhibit Life Functions”
How Can We Measure Yeast Viability?
1. Cell Replication
2. “Vital” Stains
3. Specialised Methods
Methylene Blue the best method to check Viability of Yeast
Advantages
• Rapid
• Inexpensive
• Simple
Disadvantages
• Unreliable Below 90%
• Stains Buds and Not Mothers
• Variation in Dye Intensity - Subjective
Why evaluation of pitching yeast?
quality products in a cost-effective manner, despite
the stresses that are clearly evident in modern
brewery environments, e.g.
- Ethanol
- CO2 Toxicity
- Nutrient Limitation
- Cold Shock
2. Achievement of this does require the undivided
attention of the brewer, who needs to monitor not
only yeast performance but all aspects of the
production process that can influence this
performance.
3. To overcome deterioration of yeast performance,
the brewer may turn to overpitching, increased
oxygenation or higher pitching temperature,……but
it is bound to fail if the yeast is dead or
overstressed.
4. Therefore it is imperative to measure and evaluate
pitching yeast quality
5. The scientists still do not know all details of yeast
physiology, but we have a number of indicative,
analytical tools to measure pitching yeast quality
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