General winemaking options Flashcards
The role of oxygen and sulfur dioxide in winemaking
These two gases play fundamental roles in winemaking and maturation from grape reception until after the wine is packed
Whetter and how the winemaker chooses to use or avoid these gases will have a significant effect on the style and quality of the wine
Timing and amount of oxygen exposure is key, making the difference between positive or negative effects
Oxygen can favor the growth of spoilage microbes, such as acetic acid bacteria (VA) and Brettanomyces, wines need to be carefully monitored for these microbes and there associated faults
Reductive or protective winemaking
The practice of minimizing oxygen exposure during the winemaking process
The effect of oxygen on the must or wine can be limited by (5):
Avoiding ullage:
Ullage is the headspace of air between the wine and the top of the container. Avoided by filling up the vessels to the top. Vessels that are not completely air tight (wood) may lose some liquid through air evaporation. These vessels should be topped up regularly with more wine to avoid ullage.
Use of inert gases:
Nitrogen, carbon dioxide and argon can bu used to flush out oxygen from vessels, pipes and machinery. Because these gases do not interact with compound in the wine, it 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.
Addition of sulfur dioxide
Use of impermeable containers:
Stainless steel and thick concrete vessels are impermeable to oxygen. The use of glass bottles with screw cap can also minimize exposure to oxygen during storage in bottle.
Cool constant temperatures:
Slow the rate of oxidation reactions; hence the reason for maturing wines in relatively cool cellars and picking grapes early in the morning so that the fruit is not warm.
Benefits of controlled exposer to oxygen:
Oxygen is required at the start of fermentation of all wines to promote growth of a healthy yeast population. A lack of oxygen in winemaking can lead to reductive off-flavors
In some cases. Exposure to oxygen before fermentation is thought to lead to greater oxidation stability in the wine, increasing aging 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, which can give a greater range and diversity of characteristics. Fresh fruit becomes dry fruit, notes of honey, caramel, leather and toffee can also develop.
Oxidation reactions in winemaking
Oxygen is generally a threat for the production of fresh and fruity wines. Many aroma compounds that give these wines their fruity style, for example Thiols (Sauvignon Blanc), break down in the presence of oxygen, leading to a loss of fruitiness
Also, the products of oxidation reactions may contribute to unwanted aromas in the wine: acetaldehyde, from the oxidation of ethanol) gan give nutty, apple aroma. The colour of white wines can also turn darker, brown and therefore need greater protection
Oxygen exposure can be increased by (5):
Use of cap management techniques in red wine fermentation that spray of splash the must/wine over the cap
use of small wooden barrels that can only contain a small volume of wine relative to the ingress of oxygen through the vessel
Increasing the number of rankings or amount of lees stirring during aging
Allowing ullage in wine containers with the use of inert gases
Use of techniques that involve pumping oxygen through the must or wine (hyperoxidation)
Sulfor dioxide
Is a preservative (conserveermiddel) almost universally used in winemaking and has the following properties:
Anti-oxidant:
It reduces the effects of oxidation by reacting with the products of oxidation reactions, so they cannot oxidise further compounds in the wine
Anti-microbial:
It slows down the development of microbes such as yeast and bacteria
Good winery hygiene and effective grape sorting and limiting oxygen exposure, keeping grapes/must/wine and cool temperatures can reduce the amount of SO2 needed to protect the must and wine from oxidation and microbial spoilage
A small amount of SO2 (10 mg/l) or less is naturally produced during fermentation
Maximium concentration levels of SO2
EU:
- Max 160 mg/l for red wines
- Max 210 mg/l for white wines
Maximum permitted levels for organic wines are lower than for non-organic wines
In the USA SO2 additions are not allowed for organic wines
In general, producers of natural wines may choose to avoid the use of SO2 or only use a very small amount
The concentrations of SO2 in wines are far below toxic levels, however some people can experience allergic reactions. If the wine contains over 10 mg/l the label must state that the wine contains sulfites
The transport of hand harvest fruit to the winery
Transporting grapes in small crates:
- Quality purpose or small scale grape growing
- Small crates mean minimal crushing of grapes and therefore limited oxidation and microbial spoilage
Transporting small crates tipped into large bins:
- Involves some crushing of the grapes, potential oxidation and microbial spoilage
- Some growers will add some so2 to minimize oxidation and microbial spoilage
The transport of machine harvest fruit to the winery
- Machine harvest fruit has already been destemmed and is therefore transposes as grapes in larger containers, with some release of juice
- Also here, some grape growers may choose to add some so2 at this point, typically larger estates
Measure that can be taken to minimize the risk of oxidation and microbial spoilage at harvest time
- Harvesting grapes at night when temperatures are lower, or at sunrise for hand harvesting
- Addition of so2 for its anti-oxidant and anti-microbial properties ate the time of harvesting
- Reduction of the grapes temperatures by putting them in a cold storage room once received at the winery
- Sanitizing harvest equipment/bins
Handlings after grape reception at the winery (4)
Chilling
Sorting
Destemming
Crushing
Chilling
- The winemaker may chill warm grapes (picked in the sunny afternoon) at low temperatures before crushing and pressing
- Warm temp increase the rose of oxidation, chilling helps to preserve fruity aromas
- Usually takes place in a refrigeration unit but a heat exchanger can also be used to chill (or heat) the grapes
- Both refrigerators as heat exchangers add to the costs in terms of equipment and energy. Where possible harvesting at night or early in the morning to avoid these costs
Sorting
The level of grape sorting (triage) that is required depends on a number of factors:
- Ripeness and health of the grapes
- The intended final wine quality and price
- Weather any sorting has been carried out in the vineyard (skilled hand pickers)
- Physical state of the grapes
The more sorting, the higher the cost:
- Labour requirement and time take for hand sorting
- Greater selection often results in less yields
A judgement has to be made as the level of sorting justifies in relation to the return expected from the sales of the wine
In cooler vintages, greater selection may simply be required to remove underripe or mouldy grapes (which adds to the cost)
In warm years, with nearly perfect fruit conditions, MOG may still need to be removed
Grapes for inexpensive wines may not be sorted at all
Sorting options for quality wines
- Removing unwanted grapes/bunches before picking or during hand harvesting
- Sorting by hand on a table or a moving or vibrating belt (which also removes MOG) before of after destemming
- Optical sorting, a high tech, high cost option that used digital imaging and software technology to scan individual grapes and removes them. Typical for high value grapes, for example Grand Cru Classe estates in Bordeaux
Destemming
Most white and many red hand harvested grapes are destemmed upon arrival at the winery
Destemmers work by a series of blades within a rotating drum that remove the grapes from the stems. Grapes fall out through the holes in the drum
Stems contain tannins, which can be extracted if the stems are left in contact whit the wine. These are not wanted in white wines but can be desired in some red wines. Although, if not ope, the can give unwanted green flavors and bitter tannins to the wine
Grapes are not destemmed for wined made in certain ways, examples are:
Red wine fermentations that use whole bunches, for example Pinot Noir in Burgundy or Sonoma
Wines made by carbonic maceration, for example Gamay in Beaujolais
Whole bunch pressing for some white wines, common for high-quality sparkling wines
Crushing
Crushing is the application of sufficient pressure to the grapes to break the skins and realize the juice, making it available for fermentation.
Its important that the pressure is applied gentle enough not to crush the seeds, which would add bitterness
Traditionally done by feet
The mixture of grape juice, pulp, skins, seeds that comes from the crusher is termed ‘must’
Crushing is not to be confused with pressing, which is the separation of the juice air wine form the skins and seeds
Pressing
In white winemaking grapes are almost always pressed to extract the juice from the grapes and to operate the skins from the juice before fermentation
In red winemaking grapes are typically crushed before fermentation and pressed after the desired number of days on the skins or at the end of fermentation
Pneumatic presses
Most popular press around the world, also called air bag press
Made up of a cylindrical cage with a bladder that runs owns the side or middle of it. Grapes are loaded into the tank on one side of the bladder. The other side is filled with air, and the bladder inflates, the grapes are pushed against grates on the side of the cage, separating the juice or wine from the skins
Advantages;
- Can be programmed to exert different amounts of pressure (light, less extraction / harder, greater extraction)
- Can be flushed with inert gas before use to protect the juice or wine form oxidations
They are common in wine regions around the world in medium to large-scale wineries that can afford the initial investment
Basket press
More traditional, also called vertical presses or champagne presses
A basket is filled with grapes and pressure is applied form above. The juice or wine runs through gaps or holes in the side of the basket and is collected by a tray at the bottom of the press. A pipe transfers the juice or wine to another vessel.
The vessels are not sealed, and therefor cannot be flushed with inert gases to avoid oxygen exposure
Some winemakers believe these to be gentler than pneumatic presses but they generally hold a smaller press load, are more labour intensive and therefore most suited to small wineries making premium wines.
Continuos press
Allows grapes to be continually loaded into the press as it works by using a screw mechanism; allowing quicker pressing of large volume of grapes
However, it is less gentle than pneumatic and basket presses and therefore best suited to produce high volumes of inexpensive wines
