D1: General winemaking options Flashcards
Oxygen is responsible for a number of reactions that occur between the compounds in grape must or wine and for this reason can have a significant effect on wine style and quality.
Although oxygen itself is not very reactive with many compounds in must and wine
The reaction it does take part in create products that then go on to react with many must and wine compounds
— these reactions are oxidation reactions
- the timing and amount of oxygen exposure is key, making the difference between positive or negative effect
- an understanding role of oxygen is essential
why isoxygen a general threath for the production of fresh fruity winestyles ?
1) many of the aroma compounds that give these wines their fruity character, (eg thiols in sauv b) break down in the presence of oxygen
- – this can lead to a loss of fruitiness
2) The products of oxidation may contribute to unwanted aromas to the wine: ex: acetaldehyde (from the oxidation of ethanol)
- – can give the nutty apple aroma
What does oxidation do with the color of the wine ?
1) White wines: turn darker, becoming gold and then brown with increased oxidation
* therefore white wines tend to need greter protection
2) phenolic compounds in red wines have an anti-oxidative effect, which means that they can absorb more oxygen before such effects are perceptible
How is the practice of minimising oxygen often called ?
Reductive or protective winemaking
How can the effect of oxygen to the must of wine be limited ?
1) avoiding ullage in vessels:
- - ullage is the headspace of air between the wine and the top of the container
- it can be avoided by:
* ensuring vessels are filled to the top
* if using wooden barrels there may be a gradual loss of liquid through evaporation
- - therefore, these vessels should be topped up regularly with more wine to avoid ullage
2) Use of inert gases: nitrogen, carbon dioxide and argon can be used to flush out oxygen from vessels, pipes and machinery (presses)
- - these gases do not react with compounds in the wine
- - can also be used to fill up the empty headspace of any containers where the wine does not reach the top to prevent oxygen coming into contact with the wine
3) add of so2
4) use of impermeable containers: stainless steel r thick concrete vessels are impermeable to oxygen
- - glass bottles with screw cap also minimise exposure to oxygen during storage in bottle
5) cool constant temp: slows the rate of oxidation reactions
- - hence the reason for maturing wines in cooler conditions
- - or picking grapes in the night or early in the morning so that the fruit is not warm
How can controlled oxidation be positive for the wine ?
1) oxygen is required at the start of fermentation of all wines to promote growth of a healthy yeast population and, in some cases
- – lack of oxygen in winemaking or storage can lead to reductive off flavours (fault)
2) in production of white wines: exposure to oxygen before fermentation is thought to lead to greater oxidation stability of the wine
- — increases age potential (hyperoxidation)
3) red wines: oxygen is essential in the reaction of anthocyans and tannins
- – this leads to greater color stability
what can oxygen do to the aromas of the wine over time ?
1) it can give a greater range and diversity of characteristics:
* fresh fruit becomes dried fruit and notes such as honey, nuts, caramel, coffee, leather and mushrooms
2) a high level of oxidation is vital in some wine styles, such as olorosso sherry, madeira and tawny port
3) less extreme oxidation also contributes to the complexity of many matured white and red wines
How can oxygen exposure be increased ?
1) use of cap management techniques in red wines fermentation that spray or splash the must/ wine
2) use of small wooden barrels that only contains a small volume of wine relative to the ingress of oxygen through the bung, holes and staves
3) increasing the number of rackings or amount of lees stirring during ageing:
- - any procedures where the bung or the lid of the barrel or vessel need to be removed and the wine to be moved
* increases the oxygen exposure
4) allowing ullage in wine containers without use of inert gases
5) pumping over
Oxygen can favour the growth of spoilage microbes, such as:
1) acetic acid bacteria
2) brettanomyces
– especially if other conditions are favourable ( grape must or wine with residual sugar
- therefore wines exposed to oxygen must be carefully monitored for these microbes and their associated faults
Sulfur dioxide is a preservative (voorbehoedend) and it acts like:
1) Anti oxidant:
- only reacts with oxygen itself very slow
- - it reduces the effect of oxidation by reacting with the product of oxidation reactions
- — so they cannot oxidise further compounds in the wine
* it also inhibits (remt) oxidative enzymes
2) anti microbial:
- - inhibits the development of microbes such as yeast and bacteria
- — different species of yeast and bacteria can vary in their tolerance to so2
so2 can be applied in many forms:
gas liquid or solid:
— as sulfur dioxide, potassium metabisulfite or potassium bisulfite
what about the amounts of so2 ?
1) small amount is naturally produced during ferm (10mg/l or less)
2) max concentrations are defined by local laws as it is a toxic substance
ex: eu 160mg/l is the max permitted for red wines and 210 mg/l max for white
* sweet wines are permitted to contain higher levels
3) the max permitted levels are lower for organic wines than non organic (usa so2 is forbidden for organic wines)
4) The concentrationof so2 found in wines are far below toxic levels
however some people experience an allergic reaction even at this low levels
5) if a wine contains over 10 mg/l, the label must state that the wine contains sulfites
When adding so2 ?
1) generally soon after the grapes are picked and or reach the winery
2) it may be added at various points during the winemaking process and usually at bottling
What kind of forms does so2 haves ?
1) when added to must or wine it dissolves and some of it reacts with the compounds in the liquid
- – this proportion is called bound so 2
* ineffective agains oxidation and microbes
2) the proportion that is not bound is called free so 2:
- - the vast majority of free so2 is in a relatively inactive form
- —- small proportion exist as molecular so2 which is the most effective against microbes and oxygen
What about the ph level and so2 ?
1) the ph level of must or wine has a key effect on the efficiacy of so 2
- - a greater proportion of so2 is in the molecular form at lower ph levels
* this means a greater amount of so2 need to be added at higher ph level to protect them from oxidation and microbes
And what about timing and size of so2 additions ?
Adding a larger amount when the grapes are crushed, ad the end of malolactic conversion and at bottling is considered more effective than adding smaller amounts throughout the winemaking process
Judicious add of so2 are benfical and often necessary to produce unfaulty wines that remain unfaulty once packaged. however where possible quality conscious winemakers will aim to limit add of so2 both because of the legal restrictions listed above and because:
high levels of so2 can dull (saai) aromas and sometimes cause the wine to taste harsh
How can you reduce microbial invasion in winery and reducing the amount of additional so2 ?
1) good winery hygiene and effective grape sorting can limit the amount of harmful microbes in the wine and winery
2) limiting oxygen exposure and keeping grapes/must/wine at coll temp can also reduce the amount of so2 needed to protect from oxidation and microbial spoilage
what are the options to transport the harvesed grapes to the winery ?
1) small crates: quality purpose or small scale grapegrowing
- - small crates means minimal crushing of grapes and therefore limiting oxidation and microbial spoilage
- small crates are tipped into larger hoppers (large bins) for transport
- without protective measures this would involve some crushing of the grapes and therefore oxidation and potentially microbial spoilage
- — some grapegrower will add so2 at this moment and in the form of Potassium metabisulfite
2) machine hharvested fruit has already been destemmed and is therefore transported as grapes in larger containers with some release of the juice again microbial spoilage and oxidation
- – so adding so2 at this moment (especially for the larger estates)
Once grapes have been picked they are vulnurable to oxidation and to ambient yeasts and acetic acid bacteria (turns alc into vinegar)
all of these threats to quality, rises with higher temp
but black grapes are less vulnurable to oxidation because they contain more phenolic compounds that have anti oxidative properties
measures can be taken to minimise these threats:
- harvesting grapes at night with lower temp or harvesting at rising sunlight if harvesting by hand
- add of so2 at harvesting
- reducing grape temp by putting them in cool storage room once received at the winery
- sanitising harvesting equipments
What are the steps at the face of grape reception ?
1) chilling (eventually
2) sorting
3) destemming
4) crushing
On arrival from the harvested grapes to the winery, a number of options are possible:
it will depend on the volume, hand or machine, health and quality of the grapes
1) large volumes: a conveyor belt or screw belt (transportbanden) will be used, the former being gentler with higher quality potential
2) smaller volumes of handharvested grapes can be carried in manually or with a forklift
- - the grapes are conveyed either to the sorting phase or to the destemmer/crusher
What are the chilling options ?
1) chilling of whole bunches usually takes place in a refrigeration unit
- - chilling takes time
* this can be benefical if the sorting tables and presses and other equipment are already in use
2) heat exchanger: if the grapes are in a more fluid form
- – can also heat in cool climate and cool in warme climate
- —– more present if machine harvested than the grapes are more fluid
- both of these options incur cost in terms of equipment and energy
so where possible harvesting at night or in the early morning will keep the grapes cool and avoid these costs
What are the factors depending sorting ?
1) ripeness and health of the fruit arriving at the winery
2) intended final wine and quality and price
3) any sorting already in vineyard
4) physical state of grapes (if grape arrives in big containers the grapes at the bottom will be crushed and released juice — this is too liquid to sort)
The more sorting that is carried out, the higher the cost this is both due:
1) the labour requirement and time taken for meticulous (nauwkeurig) hand sorting and because greater scrutiny often result in lower yields
– the level of sorting need to be fit in the choise of expected sale of wine
- in poor years and and in cool climates a greater of level of sorting may simply be required to remove mouldy and under ripe grapes
- in good years grapes will be received in allmost perfect condition and less triage is needed (MOG often still needed)
- grapes for inexpensive wines may not be sorted at all (cost, machinery or labour)
what are the range of sorting options for quality wines ?
1) removing unwanted bunches or grapes before picking or during hand harvesting
2) sorting by hnd on a table or a moving or vibraion belt ( latter also removes mog) can take place before or after destemmin (sometimes both
3) optical sorting (high tech), uses digital imaging and software technology to scan individual grapes
- - machine scans a 100 grape samples chosen by the grapegrower
- - rejects grapes that not conform to the sample and the mog
* this can be done in a harvesting machine or at receptionat the winery
- – grand cru estates bordeaux
what can you tell me about destemming ?
1) Hand harvested grapes for most white and many red wines are destemmed on arrival at the winery
2) machine harvested grapes are already destemmed becuse the grapes are shaken from their stems during harvesting
3) destemmers generally work by a series of blades within a rotating drum that remove the grapes from the stems
Why destemming ?
1) stems contains tannins, which can be extracted if the stems are left in contact with the wine
- - these tannins are unwanted in white wines
- – are additional to skin/seed tannins in red wines
* so can be desirable in some wines
2) if stems not ripe they can convey unwaned green flavours and bitter tannins to the wine
Grapes are not destemmed for wines made in certain ways: ex:
1) red wine ferm that use some whole bunches (pinot noir burgundy or sonoma)
2) carbonic maceration (gamay beaujolais)
3) whole bunch pressing for some white wines (commonly for high quality sparkling wine)
The crushing stage:
1) happens at the beginning of the winemaking process
2) it is the application of sufficient pressure to the grapes to break the skins and release the juice (making it available for ferm)
– it is not to be confused with pressing (which is the separation of the juice from the skins and seeds
3) it is important that the pressure applied is gentle enough not to crush the seed, shich would add bitterness
* traditionally pressure was done by human feet
4) many wineries combines these two last processes with a combined destemmer- crusher machine
- - using this machine means that sorting can only be done at the level of whole bunches
