Topic 5- Spoilage of wines by yeast

Question 1

What is ester taint and what organisms can be responsible?

How can these organisms be controlled?

Answer 1

• high levels of ester production- ethyl acetate, methylbutyl acetate.
• most often attributed with non-sac yeasts hanseniaspora uvarum, metchnikowia pulcherrima, and Pichia Anomala.

Control

• minimising fruit damage so growth of these orgs is limited before primary ferment.
• clarification of juice as suspended solids are associated with indigenous yeast.
• inoculation with a high concentration of a healthy yeast culture that rapidly initiates fermentation as ethanol above 3-4% limits the growth of these organisms.

Question 2

What organisms are responsible for surface films?
When is it prevalent?
What are the quality implications?

Answer 2

• Candida, Metschnikowia and Pichia.
• during conservation where it forms a wrinkled film on the surface. As it becomes heavy it sinks to the bottom giving more surface to grow on.
• produce acetic acid (and its esters) and acetaldehyde. Can also consume glycerol and organic acids.

Question 3

What is the best way to control surface films?

Answer 3

• inert gas cover of ullages as these organisms grow best in aerobic conditions.
• low temperature and high ethanol concentration.
• Filtration
• local sanitation of surface using SO2 or ethanol.

Question 4

When can S. cerevisiae cause spoilage of a wine?

Answer 4

When there is residual sugar in wine and improper filtration and/or SO2 and ethanol resistant yeast are present there may be refermentation in bottle.

Sorbitol acid can also be metabolised to give a rancid taint by S. cerevisiae. Therefore sordid acid treated wines are not suitable for sparkling wine base.

Question 5

What taints can Brettanomyces be implicated in?

Answer 5

• haze formation due to fermentation in bottle
• butyric, Caproic and iso-Valeric acid.
• Mousiness (tetrahydropyridine)
• 4EP, 4EG.

mSO2 of 0.5-0.8 ppm is useful in controlling Brett.

Question 6

What is the effect of unwanted growth of Schizosaccharomyces spp. (I.e. pombe) in wine?

Answer 6

Maloalcoholic fermentation- leads to poor acid balance.

Question 7

Why is Schizosaccharomyces pombe promising for the deaidification of wine?
What are some constraints?

Answer 7

Degrades malic acid to ethanol.
Tolerant of up tp 15% ethanol and pH 2.6.
Resistant to up tp 130ppm free SO2.
Cells are immobilised which is useful for ceasing malic degradation as they can be easily removed.

Constraints are the off flavours that some strains produce.

Question 8

Which spoilage yeast am I?

• produce acetaldehyde up to 200 mg/l
• very resistant to SO2 and ethanol
• forms flocculant clumps
• Best controlled by filtration and sanitation.

Answer 8

Saccharomycodes ludwigii