What roles does yeast play during alcoholic fermentation?
• Converts the sugar to alcohol.
What are the 3 components of the pulp?
• Water
• Sugar
• Acid (tartaric & malic)
What’s the biggest threat to a wine dominated by primary aromas during the wine making process? Which antioxidant is used to prevent this threat?
• Oxygen.
• Sulfur dioxide.
(grapes are picked during the night when temp is lower)
What does protective or anaerobic winemaking entail?
• Keeping the grapes from oxygen by filling airtight winery equipment with carbon dioxide or nitrogen whilst the grapes await processing/winemaking.
What are inert vessels?
Airtight vessels:
• Stainless steel vessels - easy to clean, can be of any shape and size. Can incorporate temperature control mechanisms in the form of sleeves (outside) or coils (inside) that carry hot or cold liquid.
• Cement lined with epoxy resin - less easy to clean. Used prior to stainless. The thick concrete helps regulate temperature without expensive equipment.
What does matured aerobically mean?
• Wines that were stored in oak vessels. Small amounts of oxygen interacts with the wine to soften tannins and add complexity.
What has greater oxidative effect, small or large oak vessels?
• Small vessels like a barrique, have greater oxidative effect as they present a proportionately larger surface area of wood to the wine. (wines are rarely kept in barriques for more than 2 years)
What are the 2 effects of Sulfur dioxide (SO2) in wine?
• Antioxidant - protects the grape juice wine wine from oxygen.
• Antiseptic - SO2 is toxic to the many strains of yeast and bacteria that can cause unwanted flavors. (the principal yeast used in fermentation can tolerate SO2 unlike the rest of the yeast species)
What effect does oak vessel have on a wine and what is a particular challenge?
• Softens the wines natural tannins.
• The oak tannins gives structure and textural complexity.
• Can develop tertiary aromas.
• Hygiene can be a particular challenge in terms of moulds, bacteria and yeast. (wine can be ruined by tainted wood)
What are 4 factors to consider when selecting an oak vessel?
• Species and origin of oak (European or American)
• Size (ranges from 225l to 2000l)
• Production (the level of toasting of the actual vessel)
• Age (by the time the vessel is on its fourth usage it imparts little to no tannins and flavor)
What are these size of oak barrel called?
1. 225 litre
1.228 litre
- Barrel / Barrique
- Piece
What’s a cheaper alternate to oak?
• Staves or wood chips in an inert vessel. (oxygen can be added by small controlled quantities.)
What is free run juice?
• Comes from the crushing of the grapes as they arrive at the winery. Note, this happens before pressing & fermentation.
How does a pneumatic press work?
• An inflatable rubber tube, within a perforated, horizontal, stainless steel cylinder. Applies pressure over a larger area in a controllable way. Oxygen can be kept to a minimum.
What’s another word for grape juice?
• Must
What is must weight?
• The level of sugar in the must (grape juice).
When can a wine maker choose to add RCGM?
• Before or during fermentation. Rectified Concentrated Grape Must is a colorless, odorless and syrupy liquid that gets added when the naturally occurring must weight (sugar) is insufficient.
Note - this will enhance the alcohol as there will be more sugar for the yeast to convert. This is only allowed in certain parts of the world.
- What can be done if the acid level has fallen too far during ripening?
- Haven’t fallen sufficiently?
- Acidification - normally in the form of powdery tartaric acid. In Europes it’s only permitted in warm regions. A common treatment in warm and hot regions in the rest of the world.
- Deacidification - excess acid is naturalized by an alkaline substance. Common in cooler climates.
What is alcoholic fermentation and what are the by products?
• The conversion of sugar into alcohol and CO2 through the action of yeast.
• Heat and flavor compounds.
Which yeast species is responsible for alcoholic fermentation and why?
• Saccaromyces cerevisiae - because of its tolerance to alcohol and SO2.
What temperature is too cold & too hot for alcoholic fermentation?
• Anything below 5C or anything above 35C
- What is used to kill yeast in order to stop fermentation?
- What is done to remove yeast?
- SO2 or by adding grape spirit.
- Filtration after chilling the fermentation down to below 5C.
- What is true for commercially cultured yeast?
- What is true for ambient yeast (already existing on the grapes)
- Consistently perform and produce attractive flavors. Suitable for high volume production.
- Increases the complexability. May vary between batches and the winemaker can’t control exactly which strains is present.
- When does malolactic fermentation take place and what does it convert? Also known as MLC & MLF.
- How do you encourage & avoid MLC to take place?
- After alcoholic fermentation. Converts the tart malic acid to softer lactic acid.
- Encourage by raising the temperature and not adding SO2. Avoided by storage at cool temperature, adding SO2 or by filtering out the bacteria.
