D13: General Winemaking Options Flashcards
Describe oxygen’s impact in winemaking
1) responsible for reactions that occur between compounds in grape must or wine
2) significantly impacts style and quality
3) reactions create products which then react with must and wine compounds (oxidative reactions)
4) timing and amount of oxygen exposure has impact on whether it is positive or negative
5) can favour growth of SPOILAGE MICROBES (e.g. ACETIC ACID BACTERIA or BRETTANOMYCES) so need to ensure that wines are monitored for microbes and faults
What is an oxidative reaction?
reactions create products which then react with many must and wine compounds
What are the negative impacts of oxygen exposure
1) threatens production of fresh fruity wines
2) give unwanted aromas
3) cause discolouration
Negatives of Oxygen Exposure:
1) threatens production of fresh fruity wines
Aroma compounds which give fruitiness break down in presence of oxygen and leads to loss of fruitiness
EXAMPLE: THIOLS (Sauv B)
Negatives of Oxygen Exposure:
2) give unwanted aromas
Products of oxidation contribute to unwanted aromas
EXAMPLE: ACETALDEHYDE (from oxidation of ethanol)
gives nutty, apple aroma
Negatives of Oxygen Exposure:
3) cause discolouration
Oxidation causes white wines to turn darker, becoming gold, then brown with increased oxidation
What compounds have an anti-oxidative effect?
PHENOLIC
Phenolic compounds in red wine have anti-oxidative effect so can absorb more oxygen before such effects are perceptible
What five things can you do to limit oxygen’s effect on the must or wine?
- avoid ullage
- use inert gases
- add SO2
- use impermeable containers
- cool constant temps
Limiting Oxygen’s Effect: avoid ullage
- headspace of air between wine and top of container
- avoided by ensuring vessels are filled to top (especially those containers at risk of higher levels of evap)
- need to top up vessels regularly
Limiting Oxygen’s Effect: using inert gases
- Nitrogen, CO2 and Argon can be used to flush out oxygen from vessels, pipes and machinery
- these gases don’t react with compounds in wine
- can fill empty headspace in containers
Limiting Oxygen’s Effect: using impermeable containers
- stainless steel
- concrete
- impermeable to oxygen
- screwcap glass bottles minimise exposure during bottle storage
Limiting Oxygen’s Effect: cool constant temps
- slow rate of oxidation reactions
What are the positive impacts of oxygen exposure?
- required to start fermentation of ALL wines so as to promote growth of healthy yeast population
- lack of enough oxygen in winemaking or storage can lead to reductive off-flavours
- in some whites, exposure to oxygen pre-ferm can lead to greater oxidation stability in wine, increasing age potential
- in reds, essential in reaction between ANTHOCYANINS and TANNINS for colour stability
- good for changes in aromas/flavours in wine over time (more dried, nutty, honeyed characters)
- vital in some styles e.g. sherry, madeira, tawny port
What five techniques can you use to increase oxygen exposure?
- cap management techniques
- using small wooden barrels
- small volume of wine relative to intake of oxygen through bung hole and staves
- Increased racking/lees stirring
- increased oxygen exposure every time bung of barrel or lid is removed
- allowing ullage
- techniques involving pumping oxygen through must or wine
- HYPEROXIDATION (pumping o2 through must)
- MICRO-OXYGENATION (pumping o2 through wine)
What is the role of sulfur dioxide in winemaking?
- Preservative universally used in winemaking
Anti-oxidant
- SO2 only reacts with oxygen very slowly
- reduces effects of oxidation by reacting with products of oxidation reactions so they cannot oxidise further compounds in the wine
- inhibits oxidative enzymes
Anti-microbial
- inhibits development of microbes (e.g. yeast and bacteria)
- vary in tolerance levels to SO2
In what form is SO2 used in winemaking?
- can be gas, liquid or solid
- sulfur dioxide, potassium metabisulfite or potassium bisulfite
- small amount of SO2 produced naturally during fermentation
What are the concentration levels for SO2 in winemaking?
- max concentration levels defined by local laws as it is a toxic substance
- max permitted levels lower for organic wines
- natural wine producers may choose to not add any additional SO2
- even small amounts of SO2 can cause allergic reactions
- if over 10 mg/L, the label MUST state that wine contains sulfites
For the EU the levels are:
- 160 mg/L (red)
- 210 mg/L (white)
- sweet wines can be higher
When is SO2 added to wine?
- usually added once grapes are picked, or have reached winery
- can be added during winemaking and usually at bottling
- when added, it dissolves
- can react with compounds in liquid
What is ‘bound SO2’?
- reacts with compounds in liquid
- ineffective against oxidation and microbes
What is ‘free SO2’?
- relatively inactive
- small proportion exists as molecular SO2 and most effective against oxidation and microbes
What impact does pH have on SO2?
- key effect on efficacy of SO2
- greater proportion of free SO2 is in molecular form at lower pH levels
- therefore greater amount of SO2 needs to be added to musts and wines with higher pH to protect them from oxidation and microbes
What impact does the timing and size of SO2 dose have?
- Adding larger amount when grapes are crushed, at end of MLC and at bottling seen as more effective than smaller doses throughout winemaking process
What are the negative impacts of SO2?
- can dull wine aromas/flavours and can cause wines to taste harsh
What role does management have on SO2 used in winemaking?
- Good winery hygiene and effective grape sorting can limit harmful microbes
- limiting oxygen exposure and keeping cool temps can reduce amount of SO2 needed to protect from oxidation and microbial spoilage
What are the three transportation options to the winery and what are the pros and cons of each?
“Small crates
- could be done for quality purposes or due to size of operation “
“- minimal crushing of grapes
- therefore limited oxidation and microbial spillage “
“Large Hoppers
- small crates tipped into larger hoppers for transport to winery “
“- would involve some crushing of grapes and oxidation and potential microbial spoilage
- some growers will add SO2/Potassium Metabisulfite to minimise this “
"Machine Harvested - already destemmed - transported in large containers " "- some release of juice, oxidation etc - some growers may had SO2 - mainly seen in much larger estates "
What are the risks once the grapes are picked, and how can you minimise it?
”- Once picked, grapes at risk of oxidation, to ambient yeast and acetic acid bacteria
- threat increases at higher temps
- black grapes less at risk “
“Minimise threat by:
- harvest at night or at sunrise so temps are lower
- add SO2 at time of harvest
- put grapes in cold storage when arrive at winery
- sanitise harvest equipment and bins
“
Grape reception for large volume
- conveyor belt (gentler and higher quality)
- screw conveyor
- then moved to sorting phase or destemmer/crusher
Grape reception for small volume
- moved manually with pallet truck/forklift
Why might you chill grapes following grape reception and what would be the positives and negatives (8)
- may want to chill grapes before crushing and pressing if too warm
- warm temps increase rate of oxidation
- chilling preserves fruity aromas
- reduces risk of microbial spoilage
- takes place in refrigeration unit
- can take time which slows whole process of grape processing
- can use HEAT EXCHANGER if grapes are already in more fluid format and work very quickly
- incur costs in terms of equipment and energy
Describe ‘sorting’ and the options behind it
- AKA in french as TRIAGE
- level of sorting and how it takes places depends on several factors
- more sorting = higher cost, so therefore is it worth it in terms of style of wine being made
- poor years or cool climates made need additional sorting to remove mouldy, unripe grapes
- MOG: material other than grapes - still need removing
- inexpensive wines probably wouldn’t be sorted (due to costs)
Factors:
- ripeness and health of fruit
- quality of final wine
- any vineyard sorting
- physical state of grapes
What sorting options do you have for quality wines?
- remove unwanted grapes/bunches before picking or during hand-harvesting
Sorting by hand on table or moving/vibrating belt which can take place before or after detemming
“Optical sorting - uses digital imaging and software tech to scan individual grapes
- scans 100-grape sample chosen by grower as reference
- full-load of grapes then put through sorter and it rejects ones which aren’t up to scratch
- typical option for very high quality grapes (e.g. Bordeaux Grand Cru Classe) “
What is ‘optical sorting’?
- uses digital imaging and software tech to scan individual grapes
- scans 100-grape sample chosen by grower as reference
- full-load of grapes then put through sorter and it rejects ones which aren’t up to scratch
- typical option for very high quality grapes (e.g. Bordeaux Grand Cru Classe)
Destemming
”- hand-harvested grapes for red and white are destemmed on arrival
- series of blades within a rotating drum that removes grapes from stems
- very common in wineries around the world
- stems contain tannins which can be extracted if left in contact with wine and are not wanted in white wines.
- can convey unwanted green flavours and bitter tannins to wine “
