13. General Winemaking Options Flashcards
Why is oxygen contact generally limited for white wines, particularly fresh, fruity wines?
- Many of the aroma compounds that give these wines their fruity style, for example the thiols found in Sauvignon Blanc, break down in the presence of oxygen, and this can lead to a loss of fruitiness.
- The products of oxidation reactions may contribute unwanted aromas to the wine; for example, acetaldehyde (from the oxidation of ethanol) can give a nutty, apple aroma.
- The colour of white wines can turn darker, becoming gold and then brown with increased oxidation
Why can red wines tolerate higher levels of oxygen contact than white wines?
Phenolic compounds in red wines have an anti-oxidative effect, which means that they can absorb more oxygen before such effects are perceptible.
What can a winemaker do to limit the oxygen exposure on the must or wine?
- Avoid ullage in vessels
- Use of inert (chemically inactive) gases
- Addition of sulfar dioxide
- Use of impearmable containers (stainless steel or concrete instead of wood).
- Maintain cool, constant temperatures
What is ullage, and how can it be avoided?
Ullage is the headspace of air between the wine and the top of the container. It can be avoided by ensuring vessels are filled up to the top. In vessels that are not completely airtight, such as those made of wood, there may be a gradual loss of liquid through evaporation. Therefore, these vessels should be topped up regularly with more wine to avoid ullage.
What inert gases are used to limit oxygen contact of must and wine? Outline the process.
Gases such as nitrogen, carbon dioxide and argon can be used to flush out oxygen from vessels, pipes and machinery (such as presses) because these gases do not react with compounds in the wine. Inert gases can also be used to fill the empty headspace of any containers where the wine does not reach the top to prevent oxygen coming into contact with the wine.
Why might a winemaker want to expose must and wine to a small amount of oxygen?
- Oxygen is required at the start of fermentation to ensure a healthy population of yeast; a lack of oxygen can lead to reductive flavours.
- In white wines, some oxygen exposure is thought to lead to higher oxygen stability in wine, leading to better ageing potential.
- In red wines, oxygen is essential in the reaction between anthocyanins and tannins that leads to greater colour stability
- Exposure to oxygen over time also leads to changes in the aromas/flavours of wine, desirable depending on the style of wine being produced.
How can oxygen exposure of the wine and must be increased?
- Use of cap management techniques
- Use of small wooden barrels that can only contain a small volume of wine relative to the amount of oxygen that enters through the bung holes and stave
- Increase the amount of rackings or amount of lees stirring during ageing; any procedures that require the bung of a barrel or lid of a vessel to be removed and the wine to be moved will increase oxygen exposure
- Allowing ullage in wine containers without the use of inert gases in the headspace
- Use of techniques that involve pumping oxygen through the must (e.g. hyperoxidation) or
wine (e.g. micro-oxygenation)
What are the risks of exposing must/wine to oxygen?
Oxygen can favour the growth of spoilage organisms, such as acetic acid bacteria and Brettanomyces, especially if other conditions are favourable (e.g. grape must or wine with residual sugar). Therefore, wines exposed to oxygen must be carefully monitored for these microbes and their associated faults.
What are the two properties of sulfar dioxide?
- Anti-oxidant – SO2 only reacts with oxygen itself very slowly; it reduces the effects of oxidation by reacting with the products of oxidation reactions, so they cannot oxidise further compounds in the wine. It also inhibits oxidative enzymes.
- Anti-microbial – It inhibits the development of microbes such as yeast and bacteria. Different species of yeast and bacteria can vary in their tolerance to SO2.
In what forms can sulfar dioxide be applied to must/wine?
SO2 can be applied in various forms: gas, liquid or solid, as sulfur dioxide, potassium metabisulfite or potassium bisulfite.
How much sulfar dioxide is naturally produced during fermentation?
Around 10mg/l or less
What are the permitted SO2 levels in Australia?
250mg/l; for wines with less than 35g/l RS
300mg.l; for wines with more than 35g/l RS
What are the permitted levels of SO2 in the EU?
Red wine; 150mg/l (100 for organic)
White wine; 200mg/l (150 for organic)
Sparkling; 235g/l (205 for organic)
Botrytis/late harvest; 300mg/l (270 for organic).
These levels can increase depending on RS
What are the permitted SO2 levels in the USA?
350mg/l
SO2 additions are not permitted for organic wines
Is sulfar dioxide toxic to humans?
The concentrations of SO2 found in wine are far below toxic levels; however, even at these very low levels some people can experience an allergic reaction. If a wine contains over 10 mg/L of SO2, the label must state that the wine contains sulfites.
What is the difference between bound SO2 and free SO2?
When SO2 is added to must or wine, it dissolves and some of it reacts with compounds in the liquid. This is bound SO2 and is ineffective against against oxidation and microbes.
The proportion that is not bound is called ‘free SO2’. The vast majority of the free SO2 exists in
a relatively inactive form and a small proportion exists as molecular SO2, which is the most effective against oxidation and microbes.
What factors influence the effectiveness of SO2?
- The pH level of the must or wine has a key effect on the efficacy of SO2 in that a greater proportion of free SO2 is in the molecular form at lower pH levels. This means that a greater amount of SO2 needs to be added to musts and wines with relatively high pH to protect them from oxidation and microbes.
- The timing and size of SO2 additions also influences the effectiveness of the added SO2. Adding a larger amount when the grapes are crushed, at the end of malolactic conversion and at bottling is considered as more effective than adding smaller amounts throughout the winemaking process.
Why might a producer want to limit the use of SO2 in the winery?
- Legal restrictions
- High levels of SO2 can dull wine aromas/flavours and sometimes cause the wine to taste harsh.
What steps can a winemaker take to limit the need for SO2?
- Good winery hygiene and effective grape sorting can limit the amount of harmful microbes in the wine and the winery
- Limiting oxygen exposure and keeping grapes, must or wine at cool temperatures can reduce the amount of SO2 needed to protect from oxidation and spoilage organisms.
What are the threats when transporting grapes to the winery?
At this stage, they are vulnerable to oxidation and to ambient yeasts and acetic acid bacteria (which turn alcohol to acetic acid, i.e. vinegar). All of these threats to quality rise with higher temperatures.
What measures can be taken to minimise the threats of oxidation and microbial infection when transporting grapes to the winery?
- Harvesting and transporting grapes at night when temperatures are lower or harvesting at sunrise if harvesting by hand
- Addition of SO2 for its anti-oxidant and anti-microbial properties at the time of harvesting
- Reduction of the grapes’ temperature by putting them in a cold storage room once received at the winery
- Sanitising harvesting equipment/bins (reduces chance of microbial infection only)
- Collecting and transporting the grapes in small crates to minimise crushing (this may depend on the method of harvesting).
What are the two options of transport to the winery for hand-harvested grapes?
Hand-harvested grapes are typically put in small crates that the pickers can carry. Depending on the scale of operation, the options are;
- To transport the grapes in small crates to the winery. This may be for quality purposes or simply because of small-scale grape growing. Small crates mean minimal crushing of grapes and therefore reduce oxidation of the juice and threat from spoilage organisms.
- The small crates are tipped into larger hoppers (large bins) for transport to the winery. Without protective measures, this would involve some crushing of grapes and therefore oxidation and increased threat from spoilage organisms. Some grape growers will add SO2, generally in the form of potassium metabisulfite, at this point to minimise this
How might grapes be moved around the winery upon their arrival?
Where large volumes of grapes are to be moved on reception, then a conveyor belt or a screw conveyor will be used, the former being gentler with higher quality potential. Smaller volumes of hand-harvested grapes can be moved around manually, often with a pallet truck or forklift.
Why might a winemaker choose to chill the grapes upon their arrival to the winery?
Warm temperatures increase the rate of oxidation and therefore chilling can help preserve fruity aromas. Chilling also helps to reduce the threat from spoilage organisms.
What can a winemaker use to chill grapes on their arrival to the winery?
- Refridgeration unit; suitable for whole bunches, takes time
- Heat exchanger; Suitable if grapes are in a more fluid format (machine picked, destemmed, possibly crushed). Much quicker.
What is triage?
Sorting
What factors determine the level of sorting that is required on grape reception?
- The ripeness and health of the fruit arriving at the winery
- The intended final wine quality and price
- Whether any sorting has been carried out in the vineyard (e.g. by skilled hand-pickers)
- The physical state of the grapes (if grapes arrive in large containers, the bottom grapes will have crushed and released juice; this is too liquid to sort).
What do winemakers look for when sorting on grape reception?
- Matter other than grapes (MOG) need to be removed
- Mouldy and underripe grapes (particularly in poor years and/or cool climates).
Why might producers of high volume, inexpensive wines avoid sorting grapes on their reception?
The more sorting that is carried out, the higher the cost. This is both due to the labour and time needed for meticulous hand sorting and because greater scrutiny often results in less yield.
What are the sorting options for producers of quality wines?
- Removing unwanted grapes/bunches before picking or during hand-harvesting
- Sorting by hand on a table or a moving or vibrating belt (the latter also removes MOG); this can take place before or after destemming, or occasionally both before and after destemming
- Optical sorting, which is a high-tech, high-cost option that uses digital imaging and software technology to scan individual grapes.
How does optical sorting technology work?
The machine scans a 100-grape sample chosen by the grape grower as a reference. The full load of grapes to be sorted is then passed through the machine and it rejects individual grapes that do not conform to the sample and any MOG. This can be done either in a harvesting machine or at reception in the winery. Due to the cost of the machine and high level of selection, this option is typically only used for premium and super-premium wines.
How does a destemmer work?
Destemmers generally work by a series of blades within a rotating drum that remove the grapes from the stems.
When is destemming conducted?
Hand-harvested grapes for most white wines and many red wines are destemmed on arrival at the winery using a destemming machine.
Machine-harvested grapes are already destemmed because the grapes are shaken from their stems during harvesting.
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When might a producer choose to not destem grapes?
- Red wine fermentations that use some whole bunches (e.g. with Pinot Noir in Burgundy and many other Pinot-producing regions)
- Carbonic maceration (e.g. with Gamay in Beaujolais)
- Whole bunch pressing for some white wines (e.g. common for high-quality sparkling wine).
What is meant by crushing in winemaking?
Crushing grapes is the application of sufficient pressure to the grapes to break the skins and release the juice, making it available for fermentation.
It is important that the pressure applied is gentle enough not to crush the seeds, which would add bitterness.
Traditionally, crushing was done by the pressure of human feet.
What is must?
The mixture of grape juice, pulp, skins and seeds that comes from the crusher is commonly termed ‘must’. For white wines, must may also refer to the grape juice that is fermented (pressing and clarification means pulp, skins and seeds have been removed). Hence, in winemaking, ‘must’ typically refers to the substance that is being fermented.
What is meant by ‘pressing’ grapes?
The separation of the juice or wine from the skins and seeds
When does pressing typically occur for white and red winemaking?
In white winemaking, the grapes are almost always pressed to extract the juice from the grapes and to separate the skins from the juice before fermentation.
In red winemaking, the grapes are typically crushed before fermentation and pressed after the desired number of days on the skins or at the end of fermentation.
What is the aim of pressing for white wines?
For white wines, the aim is to crush and press the berries to maximise the release of juice but without extracting tannins from skins and seeds and to avoid excessive amounts of solids.
What is the aim of pressing for red wines?
For red wines where pressing is typically after fermentation has been completed, care must be taken not to extract excessive tannin and bitterness from skins and seeds that have been softened by being in the must for periods typically between five days and three weeks (for maceration).
How does a pneumatic press work?
The press is made up of a cylindrical cage with a bladder that runs down the side or middle of it. Grapes are loaded into the tank (on one side of the bladder). The other side of the cage is filled with air and, as the bladder inflates, the grapes are gradually pushed against grates on the side of the cage, separating the juice or wine from the skins.
What are the advantages of a pneumatic press?
The advantages of the pneumatic press are that it can be programmed to exert different amounts of pressure (light pressure for less extraction, harder pressure for greater extraction, which can provide different blending components if needed) and that it can be flushed with inert gas before use to protect the juice or wine from oxidation.
Which is more common throughout the world; pneumatic press or basket press?
Pneumatic press
What is another name for pneumatic press?
Air bag press
What kind of winemaking equipment is this?
Pneumatic press
What kind of winemaking equipment is this?
Basket press
