VINIFICATION 🍇 Flashcards
Main components in the wine
- Water
- Alcohol
- Acids
- Wine aromatics
- Residual sugar
- Glycerol
- Phenolics
Approximate percentage of water in the wine
85%
Major types of alcohol in the wine
Ethanol and higher alcohols.
Ethanol
Formed during fermentation, also known as ethyl alcohol, it’s the predominant alcohol in wine, slightly sweet smell. A sensation of sweetness, bitterness, and oral warmth. It contributes to the fullness of the body and the mouthfeel. Aromas.
Consequences of high levels of alcohol in the wine
↑ alcohol (> 14.5 abv) ⇨ ↓ wine aromas volatility ↑ bitterness ⇨ fruit concentration is needed to balance
Major acids in the wine
Tartaric and malic come from the grape (2/3 of the total acidity in a warm climate).
Lactic and acetic are produced in fermentation or malo conversion.
What acids improve
Acidity improves the structure of the wine, refreshing, in balance with fruit concentration and residual sugar. High acid leaner wine, too high tart taste, no acid flabby taste.
Perception of acidity is related to the residual of sugar (German Riesling).
Range of total acidity
The sum of all the acids is in the range of 5.5-8.5 g/l.
Range of pH
The logarithmic scale of measurement for the concentration of the effective acidity of a solution is in the range of 3-4.
Consequences of low pH in the wine
↑ microbiological stability of wine ↑ effectiveness of SO2 ↑ ageing ability ↑ bright red colour (red wine)
Types of wine aromatic compounds
- Aromas from the grapes.
- Aromas created by fermentation due to the presence of aroma precursors in grape must.
- Aromas originating from fermentation and its by-products.
- Aromas from other sources.
Aromas from the grapes - what they are, examples
Aromatic compounds that are found in the grapes.
Methoxypyrazines and rotundone.
Methoxypyrazines
Aromatic compounds that are found in the grapes. Common in Sauvignon Blanc, grassy and green pepper aroma.
Rotundone
Aromatic compounds that are found in the grapes. Common in Syrah and Grüner Veltliner, pepper aroma.
Aromas created by fermentation due to the presence of aroma precursors in grape must - what they are, examples
Compounds that are not in themselves aromatic but are building blocks which become aromatic during fermentation.
Thiols and terpenes.
Thiols
Aromas created by fermentation due to the presence of aroma precursors in grape must. Released during fermentation, 4MMP gives the box tree aromas in Sauvignon Blanc (break down in presence of oxygen), for example.
Terpenes
Aromas created by fermentation due to the presence of aroma precursors in grape must. Released during fermentation, fruity and floral aromas, linalool and geraniol give grapey aromas in Muscat, for example.
Aromas originating from fermentation and its by-products - what they are, examples
Not present in the grape, but created from fermentation and its by-products (lees).
Esters, acetaldehyde, and diacetyl.
Yeast can produce reductive sulfur compounds during fermentation and lees ageing.
Esters
Aromas compounds formed by the reaction of certain acids and alcohols, the majority created through the action of yeasts in the fermentation process, fresh and fruity aromas (aroma profile of young wines), unstable and breakdown a few months after fermentation, isoamyl acetate gives banana aroma if high concentration, for example.
Acetaldehyde
Aromas compounds due to oxidation of ethanol, it masks fresh fruit aromas, stale smell (regarded as a fault in most wines), an important component of the distinctive smell of Fino Sherry.
Diacetyl
Aromas compounds produced during fermentation (malo conversion), buttery aroma.
Aromas from other sources - what they are, examples
Aromas compounds derived from other sources. Intense scientific research to detect the origin, interaction between aromatic and non-aromatic compounds.
Vanillin and eucalyptol.
Vanillin
Aromatic compound that can be derived by wine ageing in new oak barrel.
Eucalyptol
Aromatic compound that can be volatized from eucalyptus trees by heat and absorbed in the waxy layer of the grape skins in nearby vines.
What residual sugars improve
Sweetness and body.
EU classification for sugars in still wines
- Dry/Sec/Trocken – < 4 g/l or < 9 g/l with the difference of acidity not more than 2 g;
- Medium dry/Demi-Sec/Halbtrocken – between 4-12 g/l or < 18g/l with the difference of acidity not more than 10 g;
- Medium or Medium sweet/Moelleux/Lieblich - between 12-45 g/l;
- Sweet/Doux/Süss - > 45 g/l.
Glycerol
3rd abundant part of wine (dry wines).
It derives from the sugar in grapes. High levels in wines made from botrytis-affected grapes (Tokaji) or by carbonic maceration (Beaujolais).
It gives smoothness to the texture and the perception of the fullness of the body. Sweet taste.
Phenolics - what they are, examples
Group of compounds that are in the skins, stems, and seeds.
Anthocyanins and tannins.
Anthocyanins
Colour pigments responsible for the red colour of red and rosé wines. Not very stable as single molecules (they need to combine with tannins by oxygen), colour can be altered or lost during winemaking process (lees ageing or addition of SO2). They are soluble in both the must and wine.
Key points for conventional winemaking
- Louis Pasteur identified bacteria and yeasts in 1860 to convert grape must into wine.
- Principles of:
1. temperature control;
2. use of additives and/or processing aids of many types (sugar, SO2, cultured yeast, fining agents);
3. manipulations (from simple pressing and filtration to high technology). - Manipulations and the use of additive are dictated by the style, price point required, health and ripeness of the grapes, preferences of the winemaker.
Key points for organic winemaking
- Wines with certified organically-grown grapes and restricted rules during winemaking process.
- Ecocert gives a list of allowed and not allowed operations.
- The rules vary across countries with regard to the addition of SO2. Regulated amount in EU, no addition in the USA (“wines made from organic grapes” category allows the addition of SO2).
- Certification increase the cost, issued either by associations (Organic Winegrowers New Zealand), or determined at country level (US Department of Agriculture) or by the EU.
Key points for biodynamic winemaking
- Wines with biodynamically grown grapes.
- Demeter is the main certifying association. Each country has a different standard. In the UK, natural yeasts are encouraged, but organic or, if unavailable, commercial yeasts can be used. In the USA, natural yeasts must be used, but certain classes of commercial yeast can be used if a ferment has stuck and then only on a case-by-case basis.
- Biodynamic wines are more expressive of terroir (for the winemakers).
- Certification increase the cost.
Key points for natural winemaking
- Winemakers reject many modern interventions in favour of artisan practices from the past (nothing added, nothing removed).
- Wines with the fewest possible manipulations, ambient yeasts, minimum quantity of SO2.
- No certifying body, but some associations publish their approach/standards (ViniVeri and L’Association des Vins Naturel).
- No restrictions on the grapes.
- Small batch and mid to premium prices.
- Natural wines are more expressive of terroir (for the winemakers).
Meaning of reductive/protective winemaking
The practice of minimising oxygen exposure during the winemaking processes.
How to limit the effects of oxygen in winemaking
- avoiding ullage in vessels (vessels have to be filled up to the top, evaporation in wooden vessels);
- use of inert gases (nitrogen, carbon dioxide, argon);
- addition of sulfur dioxide;
- use of impermeable containers (stainless steel and thick concrete vessels are impermeable to oxygen, wooden vessels allow gentle ingress of oxygen, screwcap can minimise exposure to oxygen);
- cool and constant temperatures (cool temperatures slow the rate of oxidation reactions).
Ullage - what it is
The headspace of air between the wine and the top of the container.
Examples of inert gases
Nitrogen, carbon dioxide, argon.
Hyperoxidation - what it is, pros/cons
Exposition of the must to large quantities of oxygen before fermentation. Compounds oxidise and turn the must brown (precipitation during fermentation and the wine returns to its normal colour).
The main aim is to produce wines that are more stable against oxidation after fermentation. It removes bitter compounds, can destroy some of the most volatile aroma compounds (no for aromatic grape varieties), better suited to neutral grape varieties such as Chardonnay (can destroy thiols and methoxypyrazines of Sauvignon Blanc).
No high costs for the equipment, but more labour.
How to increase oxygen exposure
- cap management techniques for red wines;
- small wooden barrels;
- increase the number of rackings or amount of lees stirring during ageing;
- allowing ullage without inert gases;
- pumping oxygen through the must.
Relationship between oxygen and yeast
Oxygen is required at the start of fermentation to promote the growth of a healthy yeast population.
Consequences of too many oxidation reactions
No good for the production of fresh and fruity wines. Aroma compounds that give fruity style break down in the presence of oxygen (thiols). Oxidation reactions can produce unwanted aromas (acetaldehyde), darker colour (red wines have phenolic compounds, so they have to absorb more oxygen).
Oxidation reactions - what they are
The reactions oxygen does take part in create products that then go on to react with many must and wine compounds.
Unwanted effects due to oxygen exposure
It can provide a more favourable environment for spoilage microbes (acetic acid bacteria and Brettanomyces).
Main functions of sulfur dioxide
- Anti-oxidant – it reacts with the products of oxidation reactions and it inhibits oxidative enzymes.
- Anti-microbial – no yeast and bacteria (different tolerance).
EU limits for sulfur dioxide
160 mg/l red wines
210 mg/l white wines
The minimum amount of sulfur dioxide to declare on the label
10 mg/l
When is sulfur dioxide usually added during the winemaking process?
Added usually after picking or when the grapes reach the winery, at bottling.
Bound SO2
When SO2 is added to must or wine, it dissolves and reacts with compounds; ineffective against oxidation and microbes.
Free SO2
It’s unbound to compounds; effective against oxidation and microbes.
The most effective moments to add sulfur dioxide
When the grapes are crushed, after malo, and at bottling.
Consequences of high levels of SO2
High levels of SO2 are toxic and they can dull wine aromas/flavours and sometimes cause the wine to taste harsh.
Which forms can have SO2
Gas, liquid or solid – sulfur dioxide, potassium metabisulfite or potassium bisulfite.
Ways of transport the grapes after hand harvest
Grapes are in small crates:
- grapes stay in small crates (high quality, small-scale grape growing, minimal crushing, limited oxidation and microbial spoilage);
- grapes are tipped into larger hoppers such as large bins (possibility of crushing, adding of SO2 in the form of potassium metabisulfite).
Way of transport the grapes after machine harvest
Usually larger estates. Grapes are destemmed, transport in large containers, release of juice, adding of SO2.
How to preserve grapes during transportation from vineyard to cellar
- night harvest;
- addition of SO2;
- cold storage;
- sanitising harvesting equipment/bins.
Key operations during the grape reception
- Chilling.
- Sorting.
- Destemming.
- Crushing.
Chilling - what it is, pros/cons
During grape reception phase by a refrigeration unit, heat exchanger if fluid. Warm temperatures increase the oxidation and microbial spoilage, costs for equipment and energy, useful to preserve fruity aromas, takes time.
Sorting - what it is, pros/cons
During grape reception phase by table and optical sorting, otherwise during harvest. It depends on the ripeness and health of the fruit arriving at the winery, the intended final wine quality and price, carried out in the vineyard, physical state of the grapes; cost is related to the vintage.
Destemming - what it is, pros/cons
During grape reception phase. It’s common except for red wine fermentations with whole bunch (Pinot Noir in Burgundy or Sonoma), carbonic maceration (Gamay in Beaujolais), whole bunch pressing for some white wine (high-quality sparkling wine); series of blades within a rotating drum that remove the grapes from the stems or harvest by machine; stems contain tannins.
Crushing - what it is, pros/cons
During grape reception phase. Application of sufficient pressure to the grapes to break the skins and release the juice, making it available for fermentation; gentle, combo destemming-crushing.
Must - what it is
It’s the mixture of grape juice, pulp, skins, seeds that comes from the crusher.
MOG
Matter other than grapes, during sorting, such as leaves, twigs, insects.
Pressing - what it is, types
It’s the separation of the juice or wine from the skins and seeds. In red winemaking, the grapes are typically crushed before fermentation and pressed after the desired number of days on the skins or at the end of fermentation. Four types: - Pneumatic press. - Basket press. - Horizontal screw press. - Continuous press.
Types of presses
- Pneumatic presses.
- Basket press.
- Horizontal screw press.
- Continuous press.
Pneumatic press - what it is, pros/cons
The most popular type (air bag presses). Cylindrical cage with a bladder that runs down the side or middle of it, grapes are loaded into the tank, the other side is filled with air and, as the bladder inflates, the grapes are pushed against grates, separating the juice from the skins. Programmable, possibility of inert gas, initial investment (medium to large-scale wineries).
Basket press - what it is, pros/cons
A basket is filled with grapes and pressure is applied from above, the juice runs through gaps in the side of the basket and is collected by a tray at the bottom of the press. Small press load, more labour, no possibility of inert gas.
Horizontal screw press - what it is, pros/cons
Similar to basket mounted horizontally above a rectangular draining tray. Less gentle, batch processing (clean after pressing).
Continuous press - what it is, pros/cons
Continue loading (screw mechanism), less gentle, for cheap wines.
Major must adjustments
- Enrichment.
- Reducing alcohol.
- Acidification.
- Deacidification.
Enrichment - what it is, pros/cons
Must adjustment. More sugar to have more alcohol: adding dry sugar (chaptalisation), grape must, RCGM, removing water like reverse osmosis (expensive, for high volumes), vacuum extraction (expensive, for high volumes), cryoextraction (freezing the must/wine and removing ice from it, less cost). In the EU chaptalisation is allowed within limits in the cooler parts of Europe. Warmer areas can add grape concentrate or RCGM (limits).
Potential alcohol
The amount of alcohol that would be created by fermenting all the naturally-occurring sugar in the must into alcohol.
The best time in which sugar is added into the must
When fermentation is underway because the yeasts are already active and can therefore cope better with the additional sugar in the must.
Reducing alcohol - what it is, pros/cons
Must adjustment. Adding water to the grape must in warm or hot regions, aromas/flavours are diluted (law, California). Possibility to remove alcohol from the wine in post-fermentation adjustments.
Acidification - what it is, pros/cons
Must adjustment. Only in the warmest areas by addition of tartaric acid, citric acid (no EU), malic acid (not common), lactic acid (after malo). Before (preferred, better integration), during or after fermentation. Adjustments are related to the climate (deacidification in the coolest zone, acidification in the warmest, both in the moderate-climate zone). In the EU, no possibility to chaptalize and acidify must at the same time.
The best time to apply acidification
Before fermentation to benefit from the effects of a lower pH and better integration. Otherwise during or after fermentation. Some winemaking operations (malo or tartrate stabilisation) affect total acidity and pH.
Deacidification - what it is, pros/cons
Must adjustment. Only in the coolest areas (grapes are picked not fully ripen) by calcium carbonate (chalk) or potassium carbonate, ion exchange (cost). Formation and precipitation of tartrates.
Alcoholic fermentation - what it is
Conversion of the sugar into ethanol and carbon dioxide carried out by yeast in the absence of oxygen. This conversion produces also heat.
Yeasts - what they are, right conditions, consequences of their action
Group of microscopic fungi that convert sugar into alcohol and affect aroma/flavour. Initially, yeast needs oxygen to multiply quickly, then they switch to fermentation.
Right conditions: viable temperature range, yeast nutrients (nitrogen otherwise stuck ferment and rotten egg smells, diammonium phosphate or thiamine), no oxygen.
Consequences: production of alcohol, carbon dioxide, heat, volatile acidity, SO2, wine aromatics (from aroma precursors such as thiols and many terpenes, created by yeast such as esters), glycerol. Some species or strains may also produce detectable levels of undesirable reductive sulfur compounds and acetaldehyde.
Saccharomyces cerevisiae
It’s the most common yeast, good for high acidity and high alcohol, resistant to SO2, musts to dryness.
Saccharomyces bayanus
Used for must with high potential alcohol or for re-fermenting sparkling wine.
Main types of yeasts
Ambient yeast and cultured yeast.
Ambient yeast - what it is, pros/cons
Also called wild yeast, present in the vineyard and in the winery, range of yeast species (Kloechera and Candida), most of which will die out as the alcohol rises past 5%.
✅ add complexity, free, terroir idea, marketing
❌ slow start of fermentation (volatile acidity, spoilage yeasts, bacteria, off-flavours), long fermentation or even stuck, no consistent product
Cultured yeast - what it is, pros/cons
Also called selected or commercial yeast, selected in a laboratory and then grown in volumes suitable for sale, often single strains of Saccharomyces cerevisiae, cool down the must or add SO2 to kill wild yeast before adding cultured yeast.
✅ fast fermentation, low levels of volatile, less danger from spoilage yeasts and bacteria, consistent product, large choice to influence the style
❌ industrial wine, cost
The temperature at which there is the possibility to have stuck fermentation
Above 35°C.
Range of temperatures fermentation and relative consequences in the wine style
- Cool (12-16°C) – retention of fruity aroma and flavour; ideal for fresher, fruiter white wines and rosé.
- Mid-range (17-25°C) – less fruity white wines, barrel-fermented white wines, low tannin extraction, easy-drinking fruity red wines.
- Warm (26-32°C) – maximum extraction of tannins and colour, loss of fruity aromas; ideal for powerful red wines.
Factors that temperature influences during fermentation
It determines the speed of fermentation and defines the wine style.
Ways to manage the temperature during fermentation
Temperature control by specific vessels or pumping over/délestage (release heat).
Types of fermentation vessels
- Stainless steel.
- Concrete.
- Wood.
- Plastic.
- Terracotta.
Stainless steel vessel for fermentation - pros/cons
Easy to clean, different sizes, temperature control, oxygen protection, possibility of mechanisation, initial cost.
Concrete vessel for fermentation - pros/cons
Inexpensive in the last century (large scale), high thermal inertia, auto currents (egg), expensive (egg-shaped).
Wood vessel for fermentation - pros/cons
Retains heat well, oxygen exchange, hard to clean, initially expensive, then inexpensive over the long term.
Plastic vessel for fermentation - pros/cons
Light, versatile, useful for small-batch fermentations, permeable to oxygen, no temperature control.
Terracotta vessel for fermentation - pros/cons
Historic use, small-scale production.
Malo fermentation - what it is, when it happens, how to encourage, how to inhibit, effects, where it happens
From malic acid to lactic acid and carbon dioxide (heat).
When: After alcoholic fermentation and occasionally during it (increase fruit characteristics and reduce production costs).
How to encourage: 18-22°C, moderate pH (3.3-3.5), low SO2, adding cultured lactic acid bacteria.
How to inhibit: <15°C, low pH, moderate SO2, use of enzyme lysozyme, move the wine to another part of the winery to avoid the spread of lactic acid bacteria, filtration of lactic acid bacteria.
Effects:
- reduction in acidity and rise in pH – lactic acid is weaker than malic acid, softer and smoother wine;
- some colour loss in red wines – problem for very pale red wines;
- greater microbial stability – prevention that malo spontaneously happens;
- modification of the flavour – buttery notes and increment of volatile acidity.
Where: usually malo in barrels, so ability to be able to stir the lees at the same time and better integration of the flavours, a lot of work (different temperatures).
How to encourage malo fermentation
18-22°C, moderate pH (3.3-3.5), low SO2, adding cultured lactic acid bacteria.
How to inhibit malo fermentation
<15°C, low pH, moderate SO2, use of enzyme lysozyme, move the wine to another part of the winery to avoid the spread of lactic acid bacteria, filtration of lactic acid bacteria.
Effects of malo fermentation
- reduction in acidity and rise in pH – lactic acid is weaker than malic acid, softer and smoother wine;
- some colour loss in red wines – problem for very pale red wines;
- greater microbial stability – prevention that malo spontaneously happens;
- modification of the flavour – buttery notes and increment of volatile acidity.
Post-fermentation adjustments
- Acidity.
- pH.
- Removal of alcohol.
- Colour.
Removal of alcohol (post-fermentation adjustments) - what it is, types
It’s applied to produce a reduced alcohol wine or to adjust the level of alcohol marginally. Adding water is the simplest solution (law) but reduce the intensity of flavour.
- Reverse osmosis – cross-flow filtration that removes a flavourless permeate of alcohol and water, which can be distilled to remove the alcohol. The permeate is then blended back to recreate the wine. Cost (rented or bought).
- Spinning cone – extraction of volatile aroma compounds and then alcohol removal. The flavour components are then blended back of the desired alcohol level. Only for large volumes of wine.
Reverse osmosis - what it is, pros/cons
Removal of alcohol (post-fermentation adjustments). Cross-flow filtration that removes a flavourless permeate of alcohol and water, which can be distilled to remove the alcohol. The permeate is then blended back to recreate the wine. Cost (rented or bought).
Spinning cone - what it is, pros/cons
Removal of alcohol (post-fermentation adjustments). Extraction of volatile aroma compounds and then alcohol removal. The flavour components are then blended back of the desired alcohol level. Only for large volumes of wine.
Colour (post-fermentation adjustments) - what it is
Reduction by fining the wine or enhancing by adding very small amounts of the grape-derived colouring agent (MegaPurple). Not allowed in some regions (Douro Valley).
Elements that influence the style and quality of wine during the maturation process
Oxygen, new wood, and yeast lees.
Effects of oxygen during the maturation process
- A gradual reduction in many primary aromas and development of tertiary aromas. If the wine has a structure suitable for extended ageing, quality may improve otherwise reduction.
- Influence on the colour. White wines become darker. Greater colour stability and intensity for young red wines (anthocyanins bind with tannins, which protect anthocyanins from being adsorbed by yeast lees or bleached by SO2 additions – Pinot Noir becomes paler and browner).
- Softening of tannins in red wines.
Factors that influence the speed of oxidation
The amount of oxygen exposure, the compounds in the wine and temperature (warm increases the speed).
How the oxygenation happens by the wooden vessels
Wooden vessels are the traditional method of gaining slow and gradual exposure to oxygen. Some oxygen is released from the pores in the vessels (first month) and a very small amount continues to pass through the gaps between the staves and the bung hole. Maximum exposure during any transfer of wine (racking, lees stirring, topping up). Some wine is lost during the maturation process, water and alcohol impregnate the wood, they turn to vapour and diffuse to the air outside the vessel, concentration of other components. Large surface area to volume ratio for small vessels, so more wine is lost, more topping up, more oxygen exposure.
Micro-oxygenation - what it is, pros/cons
A cheaper alternative of oxygenation process, gentle and quicker exposure than wooden vessels, use of stainless steel tanks. Used to increase colour stability and intensity, soften tannins, improve texture, and reduce herbaceous flavours. More control, possibility to integrate the influence of the oak with chips or staves. Initially, for inexpensive and mid-priced wine, now also premium and super-premium.
Temperatures of storing the wines
Storing at 8-12°C for white wines and 12-16°C for red wines. Warm temperatures speed up the ageing and create undesirable reactions in terms of wine quality.
Wine factors influenced by wooden vessels
Wooden vessel influences the wine by oxygenation and various extractable compounds (tannins and aroma compounds) that depend on the age of the vessel, the size of the vessel, the type of the wood, and the production of the vessel.
Barrique
Wooden vessel, 225 l, small volume of liquid compared to the surface area of the vessel, greater extraction from the wood and exposure to oxygen, slow return on investment, labour intensive (check the wine in more vessels), expensive, used for mid-price, premium or super-premium wines.
