D1-VINI Quiz on Pre-fermentation Clarification to Finishing Flashcards
What are the four main primary forms of must clarification?
- Flotation
- Clarifying agents
- Centrifugation
- Sedimentation
These forms of must clarification aim to reduce the amount of suspended solids within the juice. These solids include particles of grape skin, stem, and pips. If the amount of solids is too high problems can be caused in fermentation, such as increased production of hydrogen sulphide (aromas of rotten eggs). Some solids are required to ensure the yeast has enough nutrients to avoid the fermentation stopping. Therefore, free run juice probably won’t need to be clarified as the juice will not contain a high proportion of solids, but press juice will probably need to be clarified as it will contain a high level of solids.
What is the simplest form of clarification.
Sedimentation
Before sedimentation takes place, the grape juice is commonly chilled to around what temperature?
4
Why is the grape juice commonly chilled before sedimentation?
to reduce the rate of oxidation and microbial spoilage, and avoid a spontaneous fermentation.
How long will sedimentation commonly take?
12-24 hours
The size and shape of the tank dictates how long this rate of clarifying takes; it takes longer in large, tall tanks than in smaller, shorter tanks due to the depth over which the solids need to fall.
How is the process called where the clear juice is transferred to the fermentation tank leaving the sediment of solids at the bottom of the tank?
Racking
What products can be added to juice to speed up the clarification process.
Pectolytic enzymes
Pectins in the juice make it more viscous and therefore more difficult for the juice to settle efficiently. Pectolytic enzymes can greatly speed up settling by breaking down the pectins.
As this is an enzymatic reaction, efficiency of this process is temperature dependent.
Breaking them down in this manner allows a more rapid separation between the liquid juice and solids, but it only aids the clarification of the grape juice, not the wine. Some fining agents, such as bentonite, gelatine and casein, are commonly used to aid clarification of both juice and wine.
How is the process called that involves bubbling gas up through the tank of juice?
Flotation
As the bubbles of gas rise they bring with them the solid particles. The solid particles are then skimmed off the top of the vat.
Flotation speeds up the rate of clarification compared to sedimentation. True or False?
True
What is needed for flotation to be successful?
Fining agents need to be added to the juice for this technique to be successful.
What are the (dis)advantages of centrifuges?
Advantages:
- They clarify the juice quickly.
- They can also be used continuously.
- Centrifuges can be used on wine as well as juice.
Disadvantages:
- They are expensive to buy, and therefore are typically only be used in wineries needing to process large volumes of juice quickly.
- They also increase the juice’s exposure to oxygen unless the machine is flushed with inert gas.
Over-clarification or under-clarification of must can have an adverse impact on the fermentation and the final wine. Briefly describe some of the risks of over/under-clarification.
Risks to the fermentation from over-clarification can lead to a stuck fermentation as there may not be enough nutrients, which come from the solids, for the yeast to survive. The fermentation needs to be carefully monitored and yeast nutrients may need to be added if the fermentation starts to struggle.
Risks to the fermentation from under-clarification can add astringency which may not be desirable in lighter wine styles. It can also give reductive sulphur compounds that are negative for wine quality.
From the wine styles listed below, decide whether they are likely to have a high percentage of solids left after must clarification.
- Inexpensive Pinot Grigio
- Premium, full-bodied, savoury Chardonnay
- Inexpensive Gewurztraminer
- PG, Low level of solids left
- CH, High level of solids left
- GT, High level of solids left
Leaving a higher proportion of solids in the must can add complexity and texture to the final wine. Other attractive aromas are also produced during fermentation. Entry-level wines like some Pinot Grigios would not be suitable though given that the range of aromas present would already be minimal, and the winemaker would want to avoid masking them.
A winemaker may choose to use the technique of hyperoxidation on the juice before fermentation. The compounds in the grape juice that oxidise most readily are targeted.
Which results can usually be observed in the juice post-hyperoxidation?
Some volatile aroma compounds are destroyed.
Bitter compounds are softened.
The juice turns more brown.
Can produce more stable wines against oxidation after fermentation. The theory being, as the compounds in the juice oxidise they turn the juice brown; during fermentation the compounds precipitate, returning the wine to its normal colour.
Can also help to remove bitter compounds.
Can destroy some of the most volatile aroma compounds and therefore is typically better suited to neutral grape varieties such as Chardonnay
Can reduce the levels of methoxypyrazines found in Sauvignon Blanc, and therefore would not be carried out if a pronounced, herbaceous style of this wine was desired.
Which form of fermentation vessel is most appropriate for each of the following wines:
- Mid-priced Chardonnay
- Sauvignon Blanc
- Super-premium Chardonnay
- Either vessel
- SS vessel
- Small new oak barrel
Oak barrels are expensive so are often reserved for the production of premium wines. Chardonnay is a reasonably neutral grape variety which often benefits from time in oak, mid-priced wines might spend a proportion of time in oak and the rest in stainless steel to keep costs down. Sauvignon Blanc is an aromatic grape variety - winemakers will often want to preserve the volatile aroma compounds which are better preserved when fermented at a controlled, cool temperature. Also, given that stainless steel is inert, the fresh and fruity aromas of Sauvignon Blanc won’t be masked by the oak.
Sauvignon Blanc - Stainless steel: Sauvignon Blanc is aromatic and depending on the wine style, the flavours need to be preserved throughout the wine making process. Stainless steel is inert and does not impart flavour into the wine. It is also important that the temperature can be maintained at the desired level which is more easily achieved in stainless steel tanks by either inbuilt temperature control or fitting some cooling device to the tank.
Premium Chardonnay - Small oak barrels: It is understood that wines that have been fermented in oak have a deeper colour and fuller body due to the oxidative environment. The wine produced has more integrated oak-derived aromas due to the action of the yeasts. It can also give the winemaker some more options for blending i.e the time spent in new oak, barrel ferment part of the juice, etc.into a new barrel.
Mid-priced Chardonnay - Either (or both) it might be fermented in both to save on cost of only using small new oak barrels and then blended later. It could be fermented in stainless steel and oak chips added to the vessel to give aromas of oak.
