General Winemaking Options Flashcards
Oxygen in must and wine
Responsible for a number of reactions that can impact style and quality. It is not very reactive with the must and wine, but reactions it is involved in create products that react with other compounds. These are oxidation reactions. Timing and amount are critical
Generally threatening for production of fresh fruity wines. Many of the compounds that give these aromas (like thiols) break down in the presence of oxygen. Products of oxidation reactions can be unwanted like acetaldehyde (oxidation of ethanol).
Color of white wines can turn darker with oxidation and so white wines need greater protection. Phenolics in red wines have anti-oxidative effect so can absorb more oxygen before effects are perceptible
Protecting wines from oxygen is called reductive or protective winemaking.
Limiting the impact of oxygen
Avoiding ullage in vessels. Ullage is head space of air b/n wine and top of container. Ensure vessels are filled to the top. Non air tight vessels like oak need regular topping up
Use of inert gases. Nitrogen, CO2, argon can be used to flush oxygen out of vessels, pipes, and machinery. Also can fill up head spaces.
Use SO2 which has strong anti oxidative effects
Impermeable containers like stainless steel and thick concrete. Glass bottles with screwcap
Cool constant temperatures slow the rate of oxidation
Positives of Oxygen Exposure
Required at start of fermentation to promote growth of yeast
In some cases, lack of oxygen can result in reductive off flavors
In some white wines exposure to oxygen pre fermentation can lead to greater oxygen stability (hyper oxidation)
Essential in red wines in the reaction b/n anthocyanins and tannins leading to color stability
Exposure over time can change aromas / flavors for a greater range. fresh fruits become dried, honey, caramel, coffee, leather, mushroom
High level of oxidation is vital in some wines like Oloroso Sherry, Madeira, Tawny Port
Increasing Oxygen exposure
Cap management techniques in red wine fermentation that splash or spray the must or wine
use of small wooden barrels that comtain a small volume of wine compared to the oxygen that enters through bung hole and staves
Increasing number of rackings or amount of lees stirring during aging or any procedure that opens the vessel or moves the wine
allowing ullage in containers and not using inert gases
Techniques that pump oxygen into the must like hyperoxidation or wine like micro oxygenation
Sulfur Dioxide Properties
Anti-oxidant: SO2 reacts with oxygen very slowly, it reduces the effect of oxygen by reacting with products of oxidation reactions so they cannot oxidize further compounds in a wine. Inhibits oxidative enzymes.
Anti-microbial: inhibits development of microbes like yeast and bacteria. Different strains have diff tolerance levels.
SO2 Application
Gas: Sulfur Dioxide; Liquid potassium metabisulfite; Solid potassium bisulfite
Small amount (10mg/L or less) is naturally produced during fermentation.
Max levels are defined locally as it is toxic. EU 150mg/L SO2 max for red and 200 for white; sweet more, organic less (none in US)
If wine is over 10mg/L must be labelled
Generally added soon after grapes are picked/or reach the winery. Various points during winemaking and at bottling.
SO2 Reactions
When added to must or wine, it dissolves and some reacts with compounds in the liquid. This is called bound SO2 and it is ineffective againsts oxidation and microbes.
The portion not bound is free SO2. The vast majority of free SO2 exists in a relatively inactive form and a small proportion as molecular SO2 which is most effective against oxidation and microbes.
pH level of must or wine has a key effect on the efficacy of SO2 in that a greater proportion of free SO2 is in the molecular form at lower pH levels. Ergo greater SO2 must be added to wines with hierh pH to protect them against oxidation and microbes.
timing and size of SO2 also influences effectiveness. Adding a larger amount at crushing, end of malo, and bottling is more effective than smaller throughout
Judicious use is beneficial and often necessary, but too much can dull the wine (and go over legal limits). Good hygiene, limited oxygen, and cool temps can reduce amount of SO2 needed to protect.
Transportation to winery
Transportation time grapes are vulnerable to oxidation, ambient yeasts, and aceitc acid bacteria (turn alcohol to acetic acid; vinegar)
These threats rise with higher temperatures. Black grapes are less vulnerable because contain more phenolic compounds with anti oxidative properties.
To minize
Harvest / transport at night when cooler or at sunrise
Add SO2 at time of harvest
Reduce temps through cold storage
Sanitizing harvest equipment: bins,
Small crates to minimize crushing
Grape Reception
Chilling
Sorting
Destemming
Crushing
Chilling
If grapes are warm upon arrival may be chilled
Warm temps increase rate of oxidation so chilling can help preserve fruity aromas. And reduce threat of spoilage bacteria
Usually in a refrigeration unit, taking time and money
Heat exchanger can be used to chill (or heat) if grapes are more fluid (machine picked, destemmed and crushed). can work very quickly
Both incur money and energy
Sorting
French Triage
Depends on: ripeness and health of fruit, intendef final quality and price, whether any sorting in the vineyard, and state of grapes (if bottom of bins crushed it will be too liquid)
More sorting higher the cost; labor, time, less yield
Judgements need to be made on level that is justifiable in relation to return expected from sales.
Poor years and cool climates may need more to remove moldy and unripe grapes. Very good years may need none.
MOG: Material other than grapes need to be removed.
Inexpensive grapes may have none at all
Quality sorting options: remove before picking or harvest; hand table, vibrating belt,
optical sorting (high tech high cost; uses digital imaging and software to scan individ grape). Machine scans a 100 grape reference sample chosen by producer. Full load processes and any grapes or MOG that do not match the sample are discarded. Can be done in a harvesting machine or at winery. Premium and super premium.
Destemming
Hand harvested grapes for most whites and many reds are destemmed (machine harvested are already)
Stems contain tannins, which can be extracted if left in contact iwth the wine. Not wanted in whites and are additional to skin and seed tannins in red wines which may or may not be desireable.
If they are not ripe they can add unwanted green flavors or bitterness.
Not destemmed for: whole bunch fermentation wines (many pinot noirs), carbonic maceration, whole bunch pressing whites
Crushing
The application of sufficient pressure to break the skins and release the juice to make it available for fermentation.
Must be gentle enough to not crush the seeds which would add bitterness. Was traditionally done with human feet.
Many wineries combine with a crusher-destemmer
the mixture coming from this machine is often called must
Pressing
In white wine almost always done before fermentation. In red grapes are crushed then fermented then pressed after desired time on skins
Soft pressing important. white; maximize release of juice without extracting tannins from skins and seeds and avoid excessive solids. Reds not extract too much tannin and bitterness from skins and seeds that are now softened from being in the must for some time.
Pneumatic Press: Most popular, called air-bag press. cylindrical cage with a bladder that runs down side or middle. Bladder inflates and gently presses the grapes against the sides of the cage. can be programmed to diff amts of pressure, flushed with inert gas.
Basket Press: traditional still used by some, aka vertical or champagne press. Basket filled with grapes and pressure from above. Juice runs through gaps in the side and collected by a tray at bottom where a pipe transfers it. Not sealed and cannot be flushed, some think they are gentler, hold a smaller load and more labor intensive, usually smaller wineries and prem wines.
Others: horizontal screw press: similar to basket but horizontal and less gentle; continuous screw press which continually feeds and less gentle.
Solids leftover called pomace
Must Enhancements
Enrichment
Acidification
Deacidification
Reducing alcohol
Adding tannin
Enrichment
Adding sugar before fermentation to increase the alcohol content of the wine
Dry sugar, grape must, grape concentratie, RCGP (flavorless syrup made from grapes). or concentrating the must (reverse osmosis, vacuum extraction, chilling).
Chaptilisation (jean Antoine Chaptal( is adding beat or cane sugar. In EU allowed within limits in cooler parts. Warmer areas cannot add sugar but can RCGM or grape concentrate within limits. added when fermentation under way so yeast can cope
Removing water from must: reverse osmosis, vacuum evaporation, cryoextraction (freezing must or wine and removing ice). First two require expensive machinery. Cryo less so. All reduce yields
Reducing Alcohol
In warm areas alcohol can rise quickly
Add water - only legal in some countries (California)
Dillutes flavors and aromas
Acidification
Routine in most warmer parts of the world
Carried out by addition of tartaric acid, but other options are citric acid (not permitted in EU); malic acid (less used as can be converted by MLF), lactic acid (used after MLF tastes less harsh)
Before, during, after fermentation, but usually before to benefit from effects of lower pH and belief that it integrates better.
However, total acidity and pH can be impacted by many processes (MLF, tartrate srabilization) so must take into account when acidifying
in EU controlled by zones. cannot champtilize and acidify same wine
Deacidification
Typically in cool climates when grapes had to be picked before fully ripe (threat of disease or weather).
Need to account for lowering of acidity due to potential MLF and tartrate stability.
Add calcium carbonate (chalk) or potassium carbonate. lowers acidity by formation and precipitation of tartrates.
High tech option is deacidification by ion exchange. Considerable investment or hiring expensive machinery. Not legal in all countries and regulated in the EU
Adding Tannins
Powdered tannins can be added to help clarify musts, stablilize color and improve mouthfeel.
Before fermentation or maturation
Alcoholic Fermentation
Conversion of sugar into ethanol (aka ethyl alcohol)and CO2 carried out by yeast in the absence of oxygen (anaerobically). Also produces heat.
Yeast
Microscopic fungi that convert sugar into alcohol and affect aroma of the wine.
Initially need oxygen to multiply quickly but then in anaerobic respiration they switch to fermentation. Nitrogen is needed or yeast stress and produce sulfur compounds or stuck fermentation. Diammonium phosphate (DAP) or thiamine (vitamine B1) can be added as yeast nutrients.
Convert sugar into alcohol in the right temperature range, access to nutrients (nitrogen), lack of oxygen.
Produce: alcohol, CO2, heat and: volatile acidity (vinegar and nail polish remover); small amounts of SO2, aromatics from aroma precursors and created by yeasts, glycerol.
Saccharomyces cerevisiae most common; can withstand high acidity and increasing high alcohol and so reliably ferments musts to dryness. Fairly resistant to SO2.
Ambient or cultured
Ambient Yeasr
aka wild yeast; present in the vineyard and winery. range of species (Kloeckera, Candida) most of which die out once alcohol is >5%.
Typically Saccharomyces cerevisiae quickly becomes dominant in wild fermenation .
Advantages: add complexity from number of yeast strains, costs nothing, can be unique to a place, use for marketing
Disadvantages: fermentation may start slowly, which is dangerous for build up of unwanted volatile acid and growth of spoilage organisms like Brettanomyces and bacteria;
Fermentation to dryness may take longer, which may not be good in a high vol winery,
increased risk of stuck fermentation which makes it vulnerable to spoilage organisms;
consistency cannot be guaranteed; a drawback for those seeking year on year consistency
Cultured yeast
ala selected or commercial yeast are selected and grown in a laboratory and then grown in to volumes for sale
often single strains of Saccharomyces cerevisiae
To use, must may be cooled down to prevent other strains from beginning to ferment. cultured added which quickly overwhelm other strains. Or add SO2 to suppress ambient and then starter batch added.
Advantages: reliable fast fermentation to dryness; low levels of volatile aciity and with speed and reliability less likelihood of spoilage organisms and bacteria; consistency; can choose a strain for desired characteristics (neutral for sparkling or one to boost aromatics)
Disadvantages: potential similarity of wines, adds cost
Temperature
The temperature of fermentation impacts the speed of fermentation and the final style.
May start relatively warm (25C) to get going and then modify.
Cool (12 - 16): fresh, fruity whites and roses; promote production and retention of esters that give fruity flavors
Mid-Range (17 - 25C): easy drinking fruity red wines to retain fruit aromas and for low tannin extract; mid of this range for fuller bodied non fruity whites, top end for barrel fermented whites.
Warm (26 - 32): red wines with pronounced flavor concentration and high tannin; max extraction of color and tannin, but may result in loss of some fruit flavors.
Above 35 fermentation may slow or stop as yeast struggle to survive.
Influencing temperature: natural conditions of cellar; today most have control within the vessels. Water or glycerin jackets or inserts monitored by computer. pump over can also reduce heat
Fermentation Vessels
Stainless Steel: Modern standard; easy to clean, large range of sizes, high control over temp. Neutral and protect from Oxygen and do not add flavors. Lots of mechanization opps (auto pump over, temp, emptying). Substantial initial investment and computers to monitor.
Concrete: Used a lot in the last century and now coming back into style due to high thermal inertia: maintain even temps better than steel. Smaller egg shaped vessels are very expensive but said to set up convection currents that mix the fermenting must and the lees during maturation.
Wood: Some areas retained large wooden fermentation casks (Alsace, Germany). Wood retains heat well and some value the small amount of oxygen that fermenting red wine in oak provides. But those pores can harbor bacteria and spoilage organisms.
Can be used multiple times but require significant initial investment. White wines may be fermented in small wood (harder for red due to cap management).
Others: Plastic (light, versatile, small batch) but permeable to oxygen and harder to temp control. Terracotta historically (amphorae, qveri, tinaja)
Malolactic Conversion
aka Malolactic fermentation; MLF
Lactic acid bacteria convert malic acid into lactic acid and CO2 and heat. Typically after alcoholic fermentation and occasionally during.
Certain conditions encourage: 18-22C temps, moderate pH (3.3 - 3.5); low total SO2. Historically happened spontaneously in spring as temps rose in cellar. Now controlled by inoculating with cultured lactic acid bacteria and ensuring optimum conditions.
Certain conditions inhibit; temps below 15, low pH, moderate SO2. Can also add enzyme lysozyme which kills the bacteria or filter them out.
Red wines routinely go through, it’s a choice for white.
Outcomes are:
Reduction in acidity and rise in pH: lactic acid is a weaker acid than malic. this may help in overly acidic wines but not in wines with overall weak acid. can make a softer smoother wine.
Some color loss in red wine: typ not a problem except in very pale wines.
Greater microbial stability: If goes through MLF during or after alcoholic fermentation this then prevents MLF from spontaneously happening later (i.e. when in bottle). However if the pH is high, raising the pH through MLF makes the wine more susceptible to spoilage organisms.
Modification of flavor: slight loss of fruit character, and addition of buttery notes and increase of volatile acidity.
Some do MLF in barrels for both red and white vs in tanks so you can stir the lees at the same time and promote better flavor integration.
Post Fermentation Adjustments
Acidity, pH, tannin can be adjusted as in pre-fermentation. But they should be small to not upset the balance of wine
Removal of alcohol
Reverse Osmosis: cross flow filtration that removes a flavorless permeate of alcohol and water which can be distilled to remove the alcohol. the watery permeate is then added back. Equipment is expensive but can be rented or bought.
Spinning Cone: Device that first extracts volatile aroma compounds from wine and then removes the alcohol. Aroma compounds are then blended back in. Only financially viable for large volumes of wine. Within EU these two means are legal but within limits
Color: reduce unwanted color tints by fining; or intensify high volume reds by adding a grape derived color agent (MegaPurple). Not permitted in some regions (i.e. Ribera del Duero).
