Lecture 2 Flashcards
What type of organism is yeast?
A eukaryote
Unicellular fungus
distantly related to moulds and mushrooms.
What genus do most ‘domesticated yeast’ belong to?
Saccharomyces genus.
Are industrial yeasts pathogenic?
No, industrial yeasts are never pathogenic.
What is the difference between lab, wild, and industrial yeast strains?
Lab strains: genetically simple, excellent for research, haploid genome;
Wild strains: found everywhere, display interesting characteristics in brewing;
Industrial strains: evolved during development of processes, robust, reliable, consistent in performance.
What are the typical shapes and sizes of Saccharomyces yeast?
Spherical or ellipsoidal, 5-10 micrometers in diameter.
Cream in colour.
What are the components of a yeast cell?
Cell wall, periplasm, cell membrane
Nucleus, vacuole, mitochondria, golgi
How do yeast cells replicate?
Mainly asexual reproduction through budding, this is most desirable so that they are all clones in industrial use
Can yeast cells bud infinitely ?
No
Cells can only bud a finite number of times, each cell has a finite lifespan.
What is the main biochemical reaction in yeast fermentation?
Glucose converts to ethanol and carbon dioxide.
What happens to yeast dry weight during fermentation?
It Increases, while the gravity decreases.
What key role does yeast play in flavor production?
Yeast influences subtle flavor differences
due to production of ethanol, higher alcohols, carbon dioxide, aldehydes, esters, sulphur compounds, vicinal diketones (VDKs like diacetyl) .
What is diacetyl and its role in brewing and winemaking?
Vicinal diketone with a butterscotch flavor, desirable in wine,
must be reabsorbed by yeast in brewing.
an intermediate in yeast metabolism (in amino acids synthesis)
What distinguishes ale from lager yeast?
Ale uses Saccharomyces cerevisiae, Lager uses Saccharomyces pastorianus.
What are the key differences between ale and lager?
Ale: more warming and estery notes; Lager: blander flavors, more sulphur; the defining factor is the type of yeast used.
Lab strains are…
genetically ‘simple’ excellecnt for basic scientific research, haploid genome. Tend to lack robustness
wild yeasts are…
found everywhere ,
often display inappropriate properties and interesting characteristics in brewing.
Industrial yeasts are…
Typically not found in the wild.
Have often evolved during the development of processes.
Are robust and produce desired effects. Are reliable and consistent in performance.
Why do yeasts make ethanol?
To obtain energy (ATP) from sugar.
In glycolysis Acetaldehyde is the terminal electron acceptor and is reduced to ethanol.
What happens to suspended cell count during fermentation.
suspended cell count first increases then decreases as the cells flocculate
