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
Must adjustments
General aim is to create a more balanced wine, especially if there has been a compromise in achieving optimum ripeness of sugars, acids, tannins and flavours.
Generally made after must clarification for white wines, but can also be made after fermentation
Enrichment
Common practices for winemakers in cooler climates to enrich the must before or during fermentation to increase the alcoholic content of the final wine
Refers to a range of practices:
- Adding dry sugar
- Adding grape must
- Adding grape concentrate
- Adding rectified concentrated grape must (RCGM - manufactured flavorless syrup from grapes)
- The process of concentration (reserve osmosis, vacuum extraction and chilling)
Chaptalisation
The common practice of adding dry sugar, named after Jean-Antoine Chaptal
Source of sugar can be from beet or cane sugar
In the EU its allowed within limits in the cooler areas of Europe, warmer areas are not permitted to add sugar, but the can add grape concentrate or RCGM, also within limits
In practice, adding sugar is one when fermentation in underway because the yeasts are already active an can therefore cope better with the additional sugar in the must
Concentrated sugar levels in must by removing water:
Reserve osmosis, vacuum evaporation or cryoextraction (freezing the must, or final wine and removing ice from it)
The first to options are expensive because of the initial outlay on the machines used and therefore are limited to wines that will have a high return on ruiners that produce high volume wines
Cryoextraction tends to cost less and so may be used more widely
Nevertheless, in all cases, the cost must take into account that after these concentration precesses there will be less wine to sell
Reducing alcohol
In warm regions where sugar accumulates quickly, it may be desired to lower the potential alcohol of the wine by adding some water to the grape must
Only legal in some countries or regions (California)
Adding water also dilutes aromas/flavours and acids
Other ways are removing alcohol form the wine (reserve osmosis or spinning cone) but these are very expensive
Acidification
In warm climates, malic acid in grapes tends to drop dramatically as the grapes ripen. If not acidified, it could lack freshness
Typically carried out by the addition of tartaric acid, other options are:
- Citric acid (not permitted in EU)
- Malic acid (less used as it could be turned into lactic acid during malolactic converison)
- Lactic acid (may be used if adjustments need to be made after malolactic conversion, less harsh than other acids)
Takes place before, during or after fermentation. But, typically before fermentation to benefit from the effects of a lower pH and because winemakers believe that the acidity added at this stage integrates better within the profile of the wine as a whole
Within the EU winemakers are not allowed to chaptalize and to acidity musts. To prevent wines being stretched by the two additions
Deacidification
In cool climates where grapes may have to be picked before fully ripe (poor weather), it may be necessary to deacidify the must or wine
Any calculation of the desired level of acidity in the final wine will need to take into account the lowering of acidity brought by malolactic conversion, if carried out
Deacidification is carried out by adding calcium carbonate (chalk) or potassium carbonate, and lowers the acidity by the formation and precipitation of tartrates
A high tech option is ion exchange which requires considerable investment or hiring expensive machinery and the producer will have to check that this option is legal in the intended country of sale
Alcoholic fermentation
The conversion of sugar into ethanol and carbon dioxide carried out by yeast in the absence of oxygen (anaerobically)
This conversion also produces heat, which need to be managed
Yeast
Collective term given to the group of microscopic fungi that convert sugar into alcohol and affect the aroma/flavour characteristics of the wine
Ambient yeast
Also called wild yeast, present in the vineyard and the winery
Include a range of species, including Kloeckera and Candida. Most of which will die out as the alcohol rises 5%
Saccharomyces cerevisiae typically becomes the dominant yeast, even in ‘wild fermentations’
Advantages/disadvantages of ambient yeast
Advantages:
- Can add complexity resulting from the presence of a number of different yeast species producing different aroma compounds
- Free to use
- Unique to place or region, supporting the idea that yeast strain contribute to the concept of terroir driven wines
- May be used as a marketing asset
Disadvantages:
- Fermentation may start slowly, dangerous for the build up of unwanted VA and the growth of spoilage yeast (Brett) and bacteria, which can lead to off-flavors
- Fermentation to dryness may take longer, which is usually not desired in a high volume winery.
- Increased risk of a stuck fermentation leaving the wine in a vulnerable state to spoilage organisms
- Consistent product can not be guaranteed, which can be a drawback for producers looking for consistency over many large vessels or across vintages
Cultured yeast
Also called selected yeast or commercial yeast are yeast strains that are selected in a laboratory and then grown in volumes suitable for sales
Often single strains of Saccharomyces cerevisiae
To use cultured yeast, the must may be cooled down to prevent fermentation by ambient yeast and then the cultured yeast is added which will quickly overwhelm the natural yeast population
Or to add so2 to the must to suppress ambient yeast. A starter batch of fermenting grape must activated with cultured yeast is than added to the tank of must to be fermented
Advantages/disadvantages of cultured yeast
Advantages:
- Produces reliably and fast fermentation to dryness
- Produces low levels of VA, given the speed and there is less danger from spoilage yeast and bacteria
- Also helps to produce a consistent product from one vintage to another
- With a wide range of cultured yeast strains available, a winemakers choice can also affect the style of wine created. Ranging from neutral yeasts for sparkling wines to yeasts which enhance the floral and fruity characteristics of aromatic varieties
Disadvantages:
- Some believe that cultured yeast leads to a certain similarity of fruit expression (industrial wine)
- Using a cultured yeast adds to the costs
Temperatures during alcoholic fermentation
The speed of fermentation is related to the temperature of the must, which in turn affects the style of wine being produced
Winemakers may favor a relatively warm start to fermentation, 25 degrees, and then monitor it regularly and cool or warm the must as required
Fermentations vessels
Stainless steel, concrete, wood
Stainless steel
Modern, easy to clean, comes in large ranges of size and enables a high degree of control over the temperature of the must or wine
Neutral vessels and very good to protect the wine from oxygen, and do not add any flavours
Most common type of vessel used in modern, high volume wineries due to price, hygiene and very high level of mechanization possible (pump-over, temperature control, automatic emptying)
High initial financial investment in thank and comprised control systems
Concrecte
Were an inexpensive option in the last century but they are know coming back into fashion of their high thermal inertia; they maintain an even temperature much more efficiently than stainless steel.
Small, egg-shaped concrete vessels (expensive) are said to set up convection currents that mix the fermenting must and mix the lees during maturation, adding complexity
Wood
Some areas in Europe have retained the use of traditinal large wooden fermentation casks (1000 liter or above Alsace, Italy)
Wood retains heat well but great care has to been taken with hygiene as the pores in the wood can harbor bacteria and spoilage organisms (Brett)
Some winemakers value the small amount of oxygen that fermenting red wine in oak provides
They can be reused many times and so they are inexpensive over the long term. However, they require capital investment when new casks are bought
As well as alcohol, carbon dioxide and heat the process of fermentation also produces (4):
- Volatile acidity (vinegar and nail polish remover smell) in standard fermentation, not enough to be noticeable
- Small amounts of natural produced so2
- Wine aromatics
Aroma precursor; No flavour in the must, but released by the action of yeast and creates aromas in the wine. Like 4MMP which gives aromas of boxwood/gooseberry in Sauvignon Blanc and terpenes which gives muscat its floral, grapey aroma
Aromas created by yeast; Esters, which give many fruity aromas (banana, carbonic maceration, Beaujolais nouveau), undesirable aromas of reductive sulfur compounds like rotten eggs/cabbage and acetaldehyde which gives aromas like bruised apple and paint thinner
- Glycerol with increases the body of the wine
Saccharomyces cerevisiae
Most common species of yeast used in winemaking
- Withstands high acidity and increasingly high alcohol levels of the must as it ferments
- Fairly resistant to so2 compared to other yeast species
- Reliably ferments musts to dryness
There are many strains within the species, which gives rise to the option to choose a strain (selection) for particular outcomes. For example the selection of a strain to boost the aromatic character in Marlborough Sauvignon Blanc
Saccharomyces
Species of yeast used for particular wines, for example for must with high potential alcohol or for re-fermenting sparkling wines
Cool fermentation temp 12-16 degrees
Fresher, fruitier white wines and rose
Cool temp promote the production and retention of fruity aromas and flavours
Mid-range fermentation temp 17-25 degrees
Easy drinking fruity reds to retain fruit aromas and lower tannin extraction
Middle of this range for less fruity white wines and top of this range for barrel-fermented white wines, to reduce the formation of fruity esters
Warm fermentation temp 26-32
Used for powerful red wines
Maximum extraction of colour and tannins, but can result in some loss of fruity aromas
Temp above 35 may slow down and yeasts struggle to survive, whit the risk of a stuck fermentation. Hence, temp needs to be controlled to prevent this from happening
Options for temp control during fermentation
- Temp can be affected by the temp of the cellar and adjusted to some extent by changing that temp
- Ferments can be moved to warmer or cooler rooms, if available and if the vessels are small enough to move
- Fermentation control installed vessels, using water or glycol in jackets that surround the vessels (stainless steel tanks) or inserts that can be put into vessels
- Pumping over (delestage) which releases heat
Malolactic conversion
Often called malolactic fermentation (MLF) is the result of lactic acid bacteria converting malic acid into lactic acid and carbon dioxide, and it produces heat
It typically happens after alcoholic fermentation and occasionally during it
Red wines routinely go through malolactic conversion, it’s a winemakers choice for when wines
Conditions that encourage malolactic conversion
- Temperatures between 18-22
- Moderate pH (3.3-3.5)
- Low total SO2
Historically it often happened spontaneously in the spring following the harvest as temperatures rose in the cellar. Now the process can be started by adding cultured lactic acid bacteria and making sure that the optimum conditions are available
Conditions that inhibit or prevent malolactic conversion
- Temperatures below 15
- Low pH and moderate levels of SO2
If winemakers want to ensure that it it’s less likely to happen, they can add the enzyme lysozyme, which kills lactic acid bacteria. Alternatively, lactic acid bacteria can be filtered out to avoid malolactic conversion taking place
The outcomes of malolactic conversions are:
Reduction in acidity and rise in pH:
Because lactic acid is weaker acid than malic acid, and may be desirable in overly acidic wines (Chardonnay cool climate) but not in wines which are already low in acidity. Overall, it results in softer, smoother styles of wine
Some colour loss in red wines:
Not problematic, except for very pale red wines
Greater microbial stability:
If the wine goes through malolactic conversion this prevent malolactic conversion from happening spontaneously at a later stage (when the wine is in the bottle) when it would be undesirable.
However, if the pH of the wine is high, raising the pH slightly makes the wine more vulnerable to spoilage organisms an may create a wine that is not refreshing because the acidity will have been decreased
Modification of the flavor:
A slight loss of fruit character may occur with the addition of buttery notes (white wines) and the process will also increase volatile acidity (nail polish remover, paint thinner)
Removal of alcohol
May be desired to produce a low alcohol wine or a wine without alcohol
Reserve osmosis
A form of cross-flow filtration that removes a flavorless permeate of alcohol and water, which can be distilled to remove the alcohol and is then bleed back to recreate the wine
Most common high-tech option. The equipment can be bought ore rented but is generally costly
Spinning cone
A device that first extracts volatile aroma compounds from wine and then removes the alcohol
The flavour compounds are than blended back into the wine of the desired alcohol level
This technology is only financially viable for large volumes of wine
Adjusting the colour of the wine
Winemakers may wish to reduce unwanted colour tints, for example by fining the wine or to enhance colour intensity by adding small amounts of the grape derived colouring agent, MegaPurple
Not permitted in al regions (for example Ribera del Duero)
