7 Flashcards
What is important for yeast quality?
Is it fit for purpose, ability of yeast to perform expectedly and produce a consistent, high-quality product.
Why is determining yeast quality important?
To meet process and product specifications, prevent use of poor quality yeast, and ensure consistent fermentation performance.
How are pitching rates determined based on yeast quality?
Based on viable cell number, tracking performance over time.
What are the key measures of yeast quality?
Viability (alive or dead), vitality (health of cell), standard fermentation characteristics, strain genetic integrity, microbiological purity.
What are the potential effects of poor quality yeast on fermentation?
Long lag phase, sluggish growth, stuck/hung fermentations, yeast autolysis, poor product quality like haze or off-flavors.
How do yeast cells divide?
Sexually via sporulation or vegetatively via budding, with most industrial yeasts only budding.
What characterizes the vegetative growth of yeast cells?
Start as a bud, finite lifespan, undergo senescence, species and strain dependent.
What is yeast necrosis and ACD?
Yeast death due to accumulated damage, known as necrosis or Accidental Cell Death.
How is yeast tolerance to stress determined?
Strain-dependent tolerance to ethanol, temperature, high gravity, osmotic stress, reactive oxygen species, oxidative stress.
How is yeast viability measured?
Direct measure through cell replication or indirect measures like membrane integrity, reduction capacity, analysis of cellular components.
What are the methods for estimating yeast viability?
Plate counts, slide counts/quartets, budding index.
What is the industry standard for yeast viability staining?
Methylene blue; advantages: rapid, inexpensive, simple; disadvantages: subjective coloration, budding cells sometimes stained.
What advantages and disadvantages does methylene blue staining have?
Methylene violet monochromic dye, stable stock solutions, reduced to colorless form by live yeast, reliable across 0-100% viability.
How are capacitance measurements used to assess yeast viability?
Live cells store electric charge, act as capacitors, dead cells do not polarize, no signal detected.
What methods are used to measure yeast vitality?
Acidification power test,
Yeast metabolism causes pH reduction in surrounding media, reflecting activity of H+ ATPase enzyme.
Vitality by measuring cell contents
High glycogen indicates healthy cells; high trehalose indicates stressed cells.
What performance tests or indicators are used to assess yeast quality?
Miniature fermentation tests, flocculation assays, sedimentation tests, hydrophobicity analysis, diacetyl uptake, metal ion release.
When should specific yeast quality tests be used?
Troubleshooting poor growth/fermentation, determining pitching rates.
What are the expected characteristics of a ‘good’ yeast culture?
Be viable and vital, quickly utilize sugars, consistently yield a product with desired characteristics, be a pure and genetically stable culture.
