General Winemaking Options (1) Flashcards
How does oxygen react with compounds in wine/must?
-oxidation reactions
-timing and amount is key
-generally threatening for fresh, fruit wines (ex: thiols in sb)
-could contribute unwanted aromas (ex: acetaldehyde or the oxidation of ethanol, nutty, bruised apple)
-favors the growth of spoilage organisms (ex: acetic acid or brettanomyces)
-white wines turn brown
-the phenolic compounds in red wine have an antioxidant effect, absorbing more oxygen before perceptible
How to limit oxygen exposure
1) avoiding ullage in vessels
2) use of inert gases (nitrogen, CO2, argon)
3) SO2
4) use of impermeable containers
5) cool, constant temperatures
When is controlled oxygen exposure a positive?
- oxygen is required at the start of fermentation for yeast to multiply
- lack of enough oxygen in winemaking or storage can lead to reductive off-flavor
- whites: exposure to oxygen before fermentation can lead to greater oxidation stability thus age ability
- reds: oxygen is essential in the reaction between anthocyanins and tannin that leads to color stability
- fresh fruits become dried, honey, caramel, coffee, leather, mushroom
- vital for some styles such as Oloroso Sherry, Madeira, and Tawny Port—
How to increase oxygen exposure?
- cap management techniques that spray or splash
- small wooden barrels
- increasing rackings and lees stirring as the bung hole must be removed
- allowing ullage
- use of techniques that pump oxygen through the must/wine (micro-oxygenation)
Why is sulphur dioxide used?
- its a preservative
- anti-oxidant: reacts with oxygen very slowly but reduces the effects of oxidation by reacting with the products of oxidation reactions so they cannot oxidize other compounds in the wine, also inhibits oxidative enzymes
- anti-microbial: inhibits the development of microbes like yeast and bacteria (varying tolerance)
How is SO2 applied?
Gas, liquid, solid, sulfur dioxide, potassium metabisulfite, or potassium bisulfite
A small amount of SO2 is also created during fermentation (up to 10 g/L)
SO2 levels
- maximum levels are defined by local laws as a toxic substance
- EU= 150 mg/L reds, 200 mg/L whites, sweets are higher
- US= wines with over 10 mg/L must state on label
When is SO2 added?
1) soon after grapes are picked or reach the winery
2) at crushing
3) after malo (bc lower acid)
4) right before bottling
Explain SO2 being added to must or wine.
- It dissolves and some of it reacts with compounds in the liquid, called ‘bound SO2’ and is ineffective against oxidation and microbes. The portion not bound is ‘free SO2’ and the vast majority is inactive but a small portion exists as molecular SO2 which is the most effective against oxidation and microbes.
- a greater proportion of free SO2 is inactive the molecular form at lower pH levels
- timing and size matter. A larger addition when grapes are crushed and at the end of malo are most effective
SO2 pros and cons
Pros:
- protects wine from faults
- anti-oxidant and anti-microbial
Cons:
- legal restrictions
- high levels can dull aromas and flavors
Threats during transportation to winery and how to reduce.
Grapes are vulnerable to oxidation, ambient yeasts, and acetic acid bacteria.
1) harvest and transport at night, when temperatures are lower
2) add SO2
3) reduce temp via refrigeration
4) sanitize equipment/bins
5) use small crates to minimize crushing rather than tippping them into larger hoppers/bins
(Machine harvesting destemmed and largely liquid)
Aspects of Grape Reception at the Winery
1) chilling
2) sorting
3) destemming
Depends on whether they have been hand or machine harvested, the health and quality of the grapes, and the volume.
Grape Reception options
Large Volumes- a conveyor belt or a screw conveyor belt are used (former is gentler)
Small Volumes- grapes can be moved manually, often with a forklift
Chilling
Warm temperatures increase the rate of oxidation (loss of fruit) and threat of spoilage so winemakers may choose chill the grapes. Picking at night or early morning can help avoid these costs.
Whole Bunches - must be refrigerated, takes time
Heat Exchanger - must be in a semi-liquid form, very fast
What does Sorting depend on?
1) the ripeness and health of the fruit
2) the intended final quality and price
3) whether any sorting was done in the vineyard
4) the physical state of the grapes
Cost of sorting
More sorting = higher cost due to the need for labour and time needed for meticulous hand sorting and lowers yields. A judgement must be made as to the level of sorting justified for the price its going to be sold.
In bad vintages more sorting will be required, in very good years may barely be needed. MOG must be sorted out at least except in the most inexpensive wines.
Sorting options for quality wine
1) remove unwanted grapes or bunches before picking or during harvest
2) sorting by hand on a table/moving belt/vibrating belt (before or after destemming)
3) optical sorting machines (high-tech, high-cost option that uses digital imaging and software technology to scan individual grapes. It scans a 100 grape sample chosen by the winemaker and rejects anything that doesn’t fit.
Destemming
Most whites and many reds are destemmed upon arrival (if hand-harvested). Destemmers work by a series of blades within a rotating drum that remove the grapes from the stems.
When is destemming not an option?
1) whole bunch fermentations for reds
2) carbonic maceration
3) whole bunch pressing for whites and reds
Crushing
The application of sufficient pressure to break the skins of the grape and release the juice. It is important that it be gentle as to not crush the seeds and add bitterness, traditionally done by feet. The mixture of grape juice, pulp, and skins is called the must, but for whites the must may refer to the fermenting grape juice.
Some wineries have destemmed-cruncher machines, only viable for whole bunches.
Pressing (red vs white)
Whites: almost always pressed to extract the juice from the grapes and to separate the skins from the juice before fermentation, soft pressing to maximize juice without extracting tannins/solids
Reds: Pressed after desired number of days on the skins or at the end of fermentation, soft pressing to avoid excess bitterness from the skins and seeds that have been softened by being in the must
Types of presses
1) Pneumatic press
2) Basket press
3) Horizontal screw press
4) Continuous press
Pneumatic Press
(compare and contrast)
- most popular, also called ‘air bag presses’
- made of a cylindrical cage with a bladder running down the center, grapes are loaded on one side of the bladder, as the bladder inflates the grapes are pushed against the grates on the side, separating the juice from the skins
- common in medium to large scale wineries that can afford the initial investment
Pros: can be programmed for more or less pressure, can be flushed with inert gas, temp control
Cons: $$$
Basket Press
(compare and contrast)
- also called ‘vertical / champagne presses’
- a basket is filled with grapes and pressure is applied from above, the juice/wine runs through gaps or holes in the side of the basket and collected by a tray at the bottom of the press, a pipe then transfers the juice or wine to another vessel
- most suited to small wineries
Pros: the most gentle
Cons: cannot avoid oxygen exposure, only small batch increasing labour
Horizontal Screw Press
(compare and contrast)
- similar to a basket press but mounted horizontally above a rectangular draining tray
- suited for small wineries
Cons: not gentle, cannot avoid oxygen exposure, small batch increasing labor
Continuous Press
(compare and contrast)
- allows grapes to be continually loaded into the press as it works by using a screw mechanism
- large volumes of inexpensive wine
Pros: allows for quicker pressings of large volumes of grapes
Cons: not gentle
Must Adjustment options
(must = pre-fermentation)
1) enrichment
2) reducing alcohol
3) acidification
4) deacidification
5) adding tannins
Adjustments before fermentation are thought to result with better integration.
Enrichment
1) adding dry sugars aka chaptalisation named after Jean-Antoine Chaptal, generally beet or cane sugar, allowed in cooler climates in the EU
2) grape must
3) grape concentrate
4) RCGM (manufactured, flavorless syrup from grapes)
5) concentration (reverse osmosis, vacuum evaporation, or the less expensive cryoextraction)
-
Reducing Alcohol
Dilution, more in other sections of the books
Acidification
- routine in warm regions for inexpensive to mid-priced wines to increase acidity and lower pH
- can be done at any point but is usually done before fermentation starts to benefit from a lower pH and have better integration
- winemaking processes (malo, tartrate stabilization) can effect total acidity and pH so the winemaker must take this into account
- controlled by the EU in bands of climate
1) tartaric acid is typical
2) citric acid in not permitted in the EU
3) malic acid could be turned to lactic
4) lactic acid is generally used after malt because it tends to taste less harsh
Enrichment examples
Zone A (Germany except Baden, UK)
8% min alcohol potential, +3% max enrichment, max 11.5-12% final alcohol
(Zone B, CI, CII, CIIIa)
Zone CIIIb (Portugal, S Spain, S Italy, Greece)
9% min alcohol potential, +1.5% max enrichment, max 13.5% final alcohol
Acid adjustment examples
Zone A (Germany except Baden, UK)
-1 to 0 g/L tartaric
Zones CI (Bordeaux, Spains Atlantic coast, Trentino-Alto Adige)
-1 to 2.5 g/L tartaric
Zone CIIIb (most of Portugal, S Spain, S Italy, S Greece)
0 to +2.5 g/L tartaric
Deacidification
- cool climates
- will need to account for the lowering of acidity brought on by malo
- carried out by adding calcium carbonate (chalk) or potassium carbonate, it lowers acidity by the formation and precipitation of tartrates
- OR the expensive high-tech option ion exchange
Adding Tannins
- powdered tannins may be added to help clarify musts, stabilize the color of musts, and improve mouthfeel
- may be before fermentation or before maturation
