Sulphite Free Wines Flashcards
Any wine containing more than __ mg/L of SO² must affix to the label “contains sulfites”
Any wine containing more than 10 mg/L of SO² must affix to the label “contains sulfites”
What are sulfites
Sulfites are naturally produced by yeast during fermentation.
Reasons for Adding Sulphites in Winemaking
They facilitate extraction of polyphenols and anthocyanins.
They prevent oxidation.
Provide antimicrobial activity.
Decrease enzymatic oxidation activity.
At low dosages (1-2 g/hl), sulphites may selectively stimulate yeast during alcoholic fermentation. Efficient on bacterias inhibition from 2g/hl (according to wine acidity).
When should we add sulphites in red and white wine?
Timing of Sulphite Additions
White Wines: Added at reception, vatting, after pressing, and before aging.
Red Wines: Added at reception, vatting, and before aging.
Factors affecting yeast growth /viability and therefore the evolution of alcoholic fermentation.
Assimilable Nitrogen level
AF temperature
Oxygen (aeration)
Level of must clarification (in white winemaking)
Vitamin level
Effects of must aeration - How oxygen influences the must?
It has a considerable impact on the growth and on the fermentation kinetics. Adding O2 during AF (5 mg/l of oxygen after 3 days) will speed up the fermentation, favoring the membrane permeability and consequently sugar uptake.
TL;DR: More oxygen, faster sugar uptake, faster AF.
How Must clarification (white wine) impacts the wine quality?
Clarifying must before the start of AF impacts the wine quality.
Too much suspended solids: heavy and unpleasant vegetal aromas
Too little suspended solids: eliminates yeast/nutrients, creates stress, but can produce higher alcohols, acetate esters (ex: isoamyl acetate).
Balance is key: measure turbidity.
Which vitamin can be added to must?
Only vitamin that can be added is thiamin (60 mg/hl)
Some yeast derived products can also contain vitamins like biotin.
What causes stuck fermentations: presence of residual sugar in wine.
→ High sugar level → More ethanol produced → Yeast intoxicated → Stuck fermentation
Excessive temperature in red wines (they will start to boil and die after 30º degrees)
Complete anaerobiosis: yeasts growth and survival is impacted, aeration is necessary.
Nutritional deficiencies: like excessive clarification, deficient must.
Inappropriate Active Dry Yeast.
Exemplify this concepts with Sauterne wine
Botrytized over-riped grapes, with high sugar concentration (>350g/L) will cause osmotic stress, leading to the high production of volatile acidity (acetate = vinegar).
→ S.cerevisiae increases the intracellular glycerol concentration in response to high osmotic pressure. This production requires a specific molecule (cofactor) NADH+. To provide NADH+, the yeast produces acetate from acetaldehyde. In conclusion: high sugar concentration leads to high volatile acidity and glycerol concentrations.
Strategies to reduce the volatile acidity?
Use a low acetate producing yeast : S.cerevisiae ST (Laffort) is recommended, used worldwide
The yeast must be adapted to the stress
Control of the available nitrogen content
Control of AF temperature
Mix 2 species : Torulaspora delbrueckii/Saccharomyces cerevisiae
