13. General Winemaking Options Flashcards
(112 cards)
1
Q
Why is oxygen contact generally limited for white wines, particularly fresh, fruity wines?
A
- Many of the aroma compounds that give these wines their fruity style, for example the thiols found in Sauvignon Blanc, break down in the presence of oxygen, and this can lead to a loss of fruitiness.
- The products of oxidation reactions may contribute unwanted aromas to the wine; for example, acetaldehyde (from the oxidation of ethanol) can give a nutty, apple aroma.
- The colour of white wines can turn darker, becoming gold and then brown with increased oxidation
2
Q
Why can red wines tolerate higher levels of oxygen contact than white wines?
A
Phenolic compounds in red wines have an anti-oxidative effect, which means that they can absorb more oxygen before such effects are perceptible.
3
Q
What can a winemaker do to limit the oxygen exposure on the must or wine?
A
- Avoid ullage in vessels
- Use of inert (chemically inactive) gases
- Addition of sulfar dioxide
- Use of impearmable containers (stainless steel or concrete instead of wood).
- Maintain cool, constant temperatures
4
Q
What is ullage, and how can it be avoided?
A
Ullage is the headspace of air between the wine and the top of the container. It can be avoided by ensuring vessels are filled up to the top. In vessels that are not completely airtight, such as those made of wood, there may be a gradual loss of liquid through evaporation. Therefore, these vessels should be topped up regularly with more wine to avoid ullage.
5
Q
What inert gases are used to limit oxygen contact of must and wine? Outline the process.
A
Gases such as nitrogen, carbon dioxide and argon can be used to flush out oxygen from vessels, pipes and machinery (such as presses) because these gases do not react with compounds in the wine. Inert gases 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.
6
Q
Why might a winemaker want to expose must and wine to a small amount of oxygen?
A
- Oxygen is required at the start of fermentation to ensure a healthy population of yeast; a lack of oxygen can lead to reductive flavours.
- In white wines, some oxygen exposure is thought to lead to higher oxygen stability in wine, leading to better ageing 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, desirable depending on the style of wine being produced.
7
Q
How can oxygen exposure of the wine and must be increased?
A
- Use of cap management techniques
- Use of small wooden barrels that can only contain a small volume of wine relative to the amount of oxygen that enters through the bung holes and stave
- Increase the amount of rackings or amount of lees stirring during ageing; any procedures that require the bung of a barrel or lid of a vessel to be removed and the wine to be moved will increase oxygen exposure
- Allowing ullage in wine containers without the use of inert gases in the headspace
- Use of techniques that involve pumping oxygen through the must (e.g. hyperoxidation) or
wine (e.g. micro-oxygenation)
8
Q
What are the risks of exposing must/wine to oxygen?
A
Oxygen can favour the growth of spoilage organisms, such as acetic acid bacteria and Brettanomyces, especially if other conditions are favourable (e.g. grape must or wine with residual sugar). Therefore, wines exposed to oxygen must be carefully monitored for these microbes and their associated faults.
9
Q
What are the two properties of sulfar dioxide?
A
- Anti-oxidant – SO2 only reacts with oxygen itself very slowly; it reduces the effects of oxidation by reacting with the products of oxidation reactions, so they cannot oxidise further compounds in the wine. It also inhibits oxidative enzymes.
- Anti-microbial – It inhibits the development of microbes such as yeast and bacteria. Different species of yeast and bacteria can vary in their tolerance to SO2.
10
Q
In what forms can sulfar dioxide be applied to must/wine?
A
SO2 can be applied in various forms: gas, liquid or solid, as sulfur dioxide, potassium metabisulfite or potassium bisulfite.
11
Q
How much sulfar dioxide is naturally produced during fermentation?
A
Around 10mg/l or less
12
Q
What are the permitted SO2 levels in Australia?
A
250mg/l; for wines with less than 35g/l RS
300mg.l; for wines with more than 35g/l RS
13
Q
What are the permitted levels of SO2 in the EU?
A
Red wine; 150mg/l (100 for organic)
White wine; 200mg/l (150 for organic)
Sparkling; 235g/l (205 for organic)
Botrytis/late harvest; 300mg/l (270 for organic).
These levels can increase depending on RS
14
Q
What are the permitted SO2 levels in the USA?
A
350mg/l
SO2 additions are not permitted for organic wines
15
Q
Is sulfar dioxide toxic to humans?
A
The concentrations of SO2 found in wine are far below toxic levels; however, even at these very low levels some people can experience an allergic reaction. If a wine contains over 10 mg/L of SO2, the label must state that the wine contains sulfites.
16
Q
What is the difference between bound SO2 and free SO2?
A
When SO2 is added to must or wine, it dissolves and some of it reacts with compounds in the liquid. This is bound SO2 and is ineffective against against oxidation and microbes.
The proportion that is not bound is called ‘free SO2’. The vast majority of the free SO2 exists in
a relatively inactive form and a small proportion exists as molecular SO2, which is the most effective against oxidation and microbes.
17
Q
What factors influence the effectiveness of SO2?
A
- The pH level of the 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. This means that a greater amount of SO2 needs to be added to musts and wines with relatively high pH to protect them from oxidation and microbes.
- The timing and size of SO2 additions also influences the effectiveness of the added SO2. Adding a larger amount when the grapes are crushed, at the end of malolactic conversion and at bottling is considered as more effective than adding smaller amounts throughout the winemaking process.
18
Q
Why might a producer want to limit the use of SO2 in the winery?
A
- Legal restrictions
- High levels of SO2 can dull wine aromas/flavours and sometimes cause the wine to taste harsh.
19
Q
What steps can a winemaker take to limit the need for SO2?
A
- Good winery hygiene and effective grape sorting can limit the amount of harmful microbes in the wine and the winery
- Limiting oxygen exposure and keeping grapes, must or wine at cool temperatures can reduce the amount of SO2 needed to protect from oxidation and spoilage organisms.
20
Q
What are the threats when transporting grapes to the winery?
A
At this stage, they are vulnerable to oxidation and to ambient yeasts and acetic acid bacteria (which turn alcohol to acetic acid, i.e. vinegar). All of these threats to quality rise with higher temperatures.
21
Q
What measures can be taken to minimise the threats of oxidation and microbial infection when transporting grapes to the winery?
A
- Harvesting and transporting grapes at night when temperatures are lower or harvesting at sunrise if harvesting by hand
- Addition of SO2 for its anti-oxidant and anti-microbial properties at the time of harvesting
- Reduction of the grapes’ temperature by putting them in a cold storage room once received at the winery
- Sanitising harvesting equipment/bins (reduces chance of microbial infection only)
- Collecting and transporting the grapes in small crates to minimise crushing (this may depend on the method of harvesting).
22
Q
What are the two options of transport to the winery for hand-harvested grapes?
A
Hand-harvested grapes are typically put in small crates that the pickers can carry. Depending on the scale of operation, the options are;
- To transport the grapes in small crates to the winery. This may be for quality purposes or simply because of small-scale grape growing. Small crates mean minimal crushing of grapes and therefore reduce oxidation of the juice and threat from spoilage organisms.
- The small crates are tipped into larger hoppers (large bins) for transport to the winery. Without protective measures, this would involve some crushing of grapes and therefore oxidation and increased threat from spoilage organisms. Some grape growers will add SO2, generally in the form of potassium metabisulfite, at this point to minimise this
23
Q
How might grapes be moved around the winery upon their arrival?
A
Where large volumes of grapes are to be moved on reception, then a conveyor belt or a screw conveyor will be used, the former being gentler with higher quality potential. Smaller volumes of hand-harvested grapes can be moved around manually, often with a pallet truck or forklift.
24
Q
Why might a winemaker choose to chill the grapes upon their arrival to the winery?
A
Warm temperatures increase the rate of oxidation and therefore chilling can help preserve fruity aromas. Chilling also helps to reduce the threat from spoilage organisms.
25
What can a winemaker use to chill grapes on their arrival to the winery?
* Refridgeration unit; suitable for whole bunches, takes time
* Heat exchanger; Suitable if grapes are in a more fluid format (machine picked, destemmed, possibly crushed). Much quicker.
26
What is triage?
Sorting
27
What factors determine the level of sorting that is required on grape reception?
* The ripeness and health of the fruit arriving at the winery
* The intended final wine quality and price
* Whether any sorting has been carried out in the vineyard (e.g. by skilled hand-pickers)
* The physical state of the grapes (if grapes arrive in large containers, the bottom grapes will have crushed and released juice; this is too liquid to sort).
28
What do winemakers look for when sorting on grape reception?
* Matter other than grapes (MOG) need to be removed
* Mouldy and underripe grapes (particularly in poor years and/or cool climates).
29
Why might producers of high volume, inexpensive wines avoid sorting grapes on their reception?
The more sorting that is carried out, the higher the cost. This is both due to the labour and time needed for meticulous hand sorting and because greater scrutiny often results in less yield.
30
What are the sorting options for producers of quality wines?
* Removing unwanted grapes/bunches before picking or during hand-harvesting
* Sorting by hand on a table or a moving or vibrating belt (the latter also removes MOG); this can take place before or after destemming, or occasionally both before and after destemming
* Optical sorting, which is a high-tech, high-cost option that uses digital imaging and software technology to scan individual grapes.
31
How does optical sorting technology work?
The machine scans a 100-grape sample chosen by the grape grower as a reference. The full load of grapes to be sorted is then passed through the machine and it rejects individual grapes that do not conform to the sample and any MOG. This can be done either in a harvesting machine or at reception in the winery. Due to the cost of the machine and high level of selection, this option is typically only used for premium and super-premium wines.
32
How does a destemmer work?
Destemmers generally work by a series of blades within a rotating drum that remove the grapes from the stems.
33
When is destemming conducted?
Hand-harvested grapes for most white wines and many red wines are destemmed on arrival at the winery using a destemming machine.
Machine-harvested grapes are already destemmed because the grapes are shaken from their stems during harvesting.
34
# hen
When might a producer choose to **not** destem grapes?
* Red wine fermentations that use some whole bunches (e.g. with Pinot Noir in Burgundy and many other Pinot-producing regions)
* Carbonic maceration (e.g. with Gamay in Beaujolais)
* Whole bunch pressing for some white wines (e.g. common for high-quality sparkling wine).
35
What is meant by crushing in winemaking?
Crushing grapes is the application of sufficient pressure to the grapes to break the skins and release the juice, making it available for fermentation.
It is important that the pressure applied is gentle enough not to crush the seeds, which would add bitterness.
Traditionally, crushing was done by the pressure of human feet.
36
What is must?
The mixture of grape juice, pulp, skins and seeds that comes from the crusher is commonly termed ‘must’. For white wines, must may also refer to the grape juice that is fermented (pressing and clarification means pulp, skins and seeds have been removed). Hence, in winemaking, ‘must’ typically refers to the substance that is being fermented.
37
What is meant by 'pressing' grapes?
The separation of the juice or wine from the skins and seeds
38
When does pressing typically occur for white and red winemaking?
In white winemaking, the grapes are almost always pressed to extract the juice from the grapes and to separate the skins from the juice before fermentation.
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.
39
What is the aim of pressing for white wines?
For white wines, the aim is to crush and press the berries to maximise the release of juice but without extracting tannins from skins and seeds and to avoid excessive amounts of solids.
40
What is the aim of pressing for red wines?
For red wines where pressing is typically after fermentation has been completed, care must be taken not to extract excessive tannin and bitterness from skins and seeds that have been softened by being in the must for periods typically between five days and three weeks (for maceration).
41
How does a pneumatic press work?
The press is made up of a cylindrical cage with a bladder that runs down the side or middle of it. Grapes are loaded into the tank (on one side of the bladder). The other side of the cage is filled with air and, as the bladder inflates, the grapes are gradually pushed against grates on the side of the cage, separating the juice or wine from the skins.
42
What are the advantages of a pneumatic press?
The advantages of the pneumatic press are that it can be programmed to exert different amounts of pressure (light pressure for less extraction, harder pressure for greater extraction, which can provide different blending components if needed) and that it can be flushed with inert gas before use to protect the juice or wine from oxidation.
43
Which is more common throughout the world; pneumatic press or basket press?
Pneumatic press
44
What is another name for pneumatic press?
Air bag press
45
What is another name for basket press?
Vertical press
Champagne press
46
How does a basket press work?
A ‘basket’ is filled with grapes and pressure is applied from 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. Basket presses are not sealed vessels, and therefore cannot be flushed with inert gases to avoid oxygen exposure.
47
Why might a winemaker choose a basket press rather than a pneumatic press?
Many winemakers believe basket presses are more gentle than pneumatic presses.
48
What are the main disadvantages of basket presses?
They generally hold a smaller press load, are much more labour intensive and are therefore most suited to small wineries making premium wines.
49
What kind of winemaking equipment is this?
Pneumatic press
50
What kind of winemaking equipment is this?
Basket press
51
What is batch pressing?
A volume of grapes is loaded into the press, they are pressed, the skins are removed, the press may be cleaned and the next batch is then loaded. This can take a lot of time.
52
What presses require batch pressing?
Penumatic, basket and horiztonal screw press
53
How does a horizontal screw press differ from a basket press?
The horizontal screw press is similar to a basket press mounted horizontally above a rectangular draining tray. It is less gentle than many other types of press and therefore less popular.
54
What are the main advantages and disadvantages of a continuous press?
The continuous press allows grapes to be continually loaded into the press (without needing batch pressing) as it works by using a screw mechanism; this allows for quicker pressing of large volumes of grapes.
However, it is also less gentle than pneumatic and basket presses and therefore best suited to producing high volumes of inexpensive wines. Consequently, they tend only to be used to produce some inexpensive, high-volume wines.
55
Name the four most common presses used around the world.
Pneumatic
Basket
Horizontal screw
Continuous
56
Why might a winemaker apply **less** pressure during pressing?
What are the disadvantages of doing this?
Applying less pressure will extract less tannin and colour from the skins, but will result in a smaller volume of juice and/or wine. There can therefore be a compromise between the quality of the juice and wine and volume of wine that can be made.
57
Why might a winemaker choose a longer press cycle for pressing?
A longer press cycle extends the contact between the skins and the juice or wine (in the case of red winemaking), which extracts more aroma/flavour and tannin.
58
What is enrichment?
It is common practice for winemakers in cooler climates to enrich the must either before or during fermentation **to increase the alcoholic content of the final wine**.
The general EU term ‘enrichment’ refers to a range of practices: adding dry sugar, grape must, grape concentrate or rectified concentrated grape must (RCGM and the processes of concentration (reverse osmosis, vacuum extraction, chilling).
59
What is chaptilisation?
Adding dry sugar to enrich the must either before or during fermentation to increase the alcoholic content of the final wine.
The souce of the sugar can be beet or cane sugar.
60
Is enrichment permitted in the EU?
Chaptilisation is permitted in cooler regions of the EU.
Warmer areas (broadly Southern Europe) are not permitted to add sugar, but they can add grape concentrate or RCGM, again within limits.
Wine regions within the EU are split into different zones that determine the level of enrichment (as well as acidification and deacidification) that is permitted.
61
What is the permitted enrichment level for EU zone A (Germany, excluding Baden Baden)?
Min. natural potential alcohol: 8%
Maximum enrichment: +3%
Maximum alcohol level in final wine (if enriched): 11.5% for white wines
12% for red wines
62
What is the permitted enrichment level for EU zone Cllb (Most of Portugal, southern Spain, parts of southern Italy and Greece)?
Minimum natural potential alcohol: 9%
Maximum enrichment:1.5%
Maximum alchol level in fine wine (if enriched) 13.5%
63
When is sugar for enrichment typically added to the must/wine?
In practice, adding sugar is done when fermentation is underway because the yeasts are already active and can therefore cope better with the additional sugar in the must.
64
Name the three methods of enrichment by concentration.
* Reverse osmosis
* Vacuum evaporation
* Cyroextraction (tends to cost less and so may be used more widely).
65
What is cyroextraction?
Freezing the must, or even the final wine, and removing ice from it
66
How is acidification carried out?
Acidification is typically carried out by the addition of tartaric acid, the acid characteristic of grapes. Other options are:
* citric acid (though not permitted in the EU for acidification)
* malic acid (less used as it could be turned into lactic acid by malolactic conversion)
* lactic acid (may be used if adjustments need to be made after malolactic conversion; it tends to taste less harsh than the other acids).
67
When would a winemaker carry out acidification?
Acidification can take place before, during or after fermentation. However, winemakers typically prefer to acidify before fermentation starts to benefit from the effects of a lower pH and because they believe that the acidity added at this stage integrates better within the profile of the wine as a whole.
68
Is acidification permitted in the EU?
In the EU, the amount of permitted acidification is controlled within the bands of countries organised according to climate.
In the coolest zone, only deacidification is allowed. In the warmest zone, acidification is allowed.
69
What are the permitted acidification adjustment levels for zoneCl (which includes Bordeaux, Spain’s cool north Atlantic coast and Italy’s Trentino-Alto Adige)?
Winemakers can deacidify or acidify according to the season (−1 to +2.5 g/L).
70
What are the permitted acidification adjustment levels for zoneCllb (Most of Portugal, southern Spain, parts southern Italy and Greece)?
0 to +2.5 g/L
71
What are the methods a winemaker can use to deacidity wine?
Deacidification is carried out by adding calcium carbonate (chalk) or potassium carbonate, and it lowers acidity by the formation and precipitation of tartrates.
high-tech option is deacidification by ion exchange. This last option requires considerable investment or hiring expensive machinery.
72
What must a winemaker consider before deacidifying wine?
* Any calculation of the desired final level of acidity will need to take account of the lowering of acidity brought about by malolactic conversion.
* The producer will need to check that this option is legal in the intended country of sale.
* Producers in the EU will need to ensure that they only deacidify within the legal limits set by EU law.
73
How and why might a producer add tannin to must?
Powdered tannins may be added to help to clarify musts and, in the case of red wines, to help to stabilise the colour of musts and improve mouthfeel.
Tannins may either be added to the must before fermentation or to the wine before maturation.
74
What adjustments can a producer make to the must/wine?
* Enrichment
* Reducing alcohol
* Acidification
* Deacidification
* Adding tannin
75
What is alcoholic fermentation and how is it carried out?
Alcoholic fermentation is the conversion of sugar into ethanol (also known as ethyl alcohol) and carbon dioxide carried out by yeast in the absence of oxygen (‘anaerobically’). This conversion also produces heat, which has to be managed.
76
What are yeasts?
Yeast is the collective term given to the group of microscopic fungi that convert sugar into alcohol and affect the aroma/flavour characteristics of wines.
77
Does yeast require oxygen for alcoholic fermentation?
Initially, yeast need oxygen to multiply quickly, but once any oxygen is used up by the yeast (in aerobic respiration), they switch to fermentation.
78
What conditions will yeast successfully convert sugars into alcohol in alcoholic fermentation?
* A viable temperature range
* Access to yeast nutrients, especially nitrogen
* The absence of oxygen (after the initial growth of yeast populations).
79
What does the alcoholic fermentation process produce?
* Alcohol, carbon dioxide and heat
* Volatile acidity
* Small amounts of SO2
* Wine aromatics;
* Glycerol
80
What is the most common strain of yeast used in winemaking and why?
Saccharomyces cerevisiae is the most common species of yeast used in winemaking. It can withstand well the high acidity and increasing alcohol level of the must as it ferments and, hence, it reliably ferments musts to dryness. It is also fairly resistant to SO2 in comparison to other yeast species.
81
What are ambient yeasts?
Ambient yeast (also called wild yeast) is present in the vineyard and the winery. It will include a range of yeast species (e.g. Kloeckera and Candida), most of which will die out as the alcohol rises past 5%. Typically, Saccharomyces cerevisiae quickly becomes the dominant yeast, even in ‘wild fermentations’.
82
What are the advantages of using ambient yeasts for alcoholic fermentation?
* Ambient yeast can add complexity resulting from the presence of a number of yeast species producing different aroma compounds.
* It costs nothing to use.
* Some studies have shown that the yeast population in a must can be unique to a place or region, especially where widely available cultured yeast has not been used.
* Using ambient yeast may also be used as part of the marketing of the wine.
83
What are the disadvantages of using ambient yeasts for alcoholic fermentation?
* Fermentation may start slowly. This can be dangerous for the build-up of unwanted volatile acidity and the growth of spoilage organisms (such as Brettanomyces) and bacteria, potentially leading to off-flavours.
* Fermentation to dryness may take longer, which may not be desirable in a high volume winery. There is also increased risk of a stuck fermentation (fermentation ceases or slows) leaving the wine in a vulnerable state to spoilage organisms.
* A consistent product cannot be guaranteed, which can be a drawback, especially for producers looking for consistency over many large vessels or across vintages.
84
What are cultured yeasts?
Cultured yeast (also sometimes called selected yeast or commercial yeast) are yeast strains that are selected in a laboratory and then grown in volumes suitable for sale. Commercially available cultured yeasts are often single strains of Saccharomyces cerevisiae.
85
How are cultured yeasts added for alcoholic fermentation?
To use cultured yeast, the must may be cooled down to prevent fermentation by ambient yeast and then the cultured yeast added, which quickly overwhelm the natural yeast population.
Another option is to add SO2 to the must to suppress ambient yeasts. A starter batch, made up of fermenting grape must which has been activated with the cultured yeast, is then added to the tank of must to be fermented.
86
What are the advantages of using cultured yeasts for alcoholic fermentation?
* Cultured yeast produces reliable, fast fermentation to dryness.
* Cultured yeast produces low levels of volatile acidity and, given its speed and reliability, there is less danger from spoilage organisms and bacteria.
* Cultured yeast also helps to produce a consistent product from one vintage to another.
* With a large selection of cultured yeast strains available commercially, the winemaker’s choice can also affect the style of wine created. For example, the winemaker may choose to use a neutral yeast for a sparkling wine base or a strain of yeast to boost the aromatic character in Sauvignon Blanc).
87
In what scenarios might the yeast strain Saccharomyces bayanus be used?
Saccharomyces bayanus is sometimes used for must with high potential alcohol or for re-fermenting sparkling wine.
88
What are the disadvantages of using cultured yeasts for alcoholic fermentation?
* Some believe that using cultured yeast leads to a certain similarity of fruit expression (and hence the charge of ‘industrial wine’).
* Using cultured yeast adds the cost of using a commercial product.
89
What can be added as yeast nutrients for alcoholic fermentation?
Nitrogen (essential)
Diammonium phosphate (known as DAP)
Thiamine (vitamin B1)
90
What are the risks if nitrogen levels are low during alcoholic fermentation?
Low levels of nitrogen can stress the yeast causing them to produce undesirable sulfur compounds (giving a rotten egg smell) or even to stop fermenting (resulting in a stuck fermentation).
91
Are warmer or cooler temperatures typically desired for the start of alcoholic fermentation?
Winemakers may prefer a relatively warm start to fermentation (e.g. 25°C) to get the yeast population established, and then monitor it regularly and cool or warm the must as required.
92
What fermentation temperatures are ideal in the production of fresh, fruiter styles of white and rosé wines? Why?
Cool temperatures between 12-16°C
Cool temperatures promote the production and retention of esters that give fruity aromas and flavours
93
What styles of wines are typically fermented at mid-range temperatures?
Mid-range: 17-25°C
* Easy-drinking fruity red wines to retain fruit aromas and for low tannin extraction
* Middle of this temperature range for less fruity white wines
* Top of this range for barrel-fermented white wines
94
What style of wines are typically fermented at warm temperatures? Why?
Warm: 26-32°C
Used for red wines with pronounced flavour concentration and high tannins
Maximum extraction of colour and tannins, but can result in some loss of fruity flavours
95
What are the risks of alcoholc fermentation occuring at high temperatures (above 35°C)?
Above 35°C the fermentation may slow down and stop as yeasts struggle to survive, with risk of a stuck fermentation. Hence, the temperature must be controlled to prevent this from happening.
96
What are a winemakers options for temperature control during alcoholic fermentation?
* Fermentation temperature can be influenced by the temperature of the cellar: sluggish ferments can be moved to a warmer room and over-heating ferments to a cooler one
* Temperature control is typically a feature installed in many vessels; these use either water or glycol in jackets that surround vessels (typically stainless steels tanks) or in inserts that can be put into vessels.
* Temperatures can also be reduced by pumping over/délestage, which releases heat.
97
What are the advantages of stainless steel vessels for fermentation?
* Easy to clean
* Comes in a range of sizes
* Enables a high degree of control over the temperature of the must or wine
* These are neutral vessels and so are very good at protecting the wine from oxygen
* They also do not add any flavours.
* Moderately priced
* Very high level of mechanisation possible (automatic pump-over, temperature control, automatic emptying, etc.)
98
Why are concrete vessels regaining popularity for alcoholic fermentation?
Because of their high thermal inertia: they maintain an even temperature much more efficiently than stainless steel.
99
Why might a producer choose to use wooden vessels for alcoholic fermentation?
* Wood retains heat well (if this is desired).
* Some winemakers value the small amount of oxygen ingress that fermenting red wine in oak provides.
* Can be used multiple times, so inexpensive over the long term
100
What are the disadvantages of using wooden vessels for alcoholic fermentation?
* Great care has to be taken with hygiene as the pores in wood can harbour bacteria and spoilage organisms.
* Require capital investment when new large oak casks are bought.
101
What are the advantages and disadvantages of using plastic vessels for alcoholic fermentation?
Plastic vessels are light, versatile and useful for small-batch fermentations. However, plastic is permeable to oxygen and it can be difficult to control the temperature in plastic vessels.
102
Name some examples of terracotta pots used for alcoholic fermention.
Amphora, qvevri (Georgia) and tinaja (Spain).
103
What is malolactic fermentation?
Malolactic conversion, often called malolactic fermentation (MLF, ‘malo’), is the result of lactic acid bacteria converting malic acid into lactic acid and carbon dioxide, and it produces heat.
104
When does malolactic conversion typically occur?
It typically happens after alcoholic fermentation and occasionally during it.
105
What conditions enocurage the onset of malolactic conversion?
18–22°C, a moderate pH (3.3–3.5) and low total SO2.
Historically, it often happened spontaneously in the spring following harvest as temperatures rose in the cellar. Now the process can be started by adding (‘inoculating with’) cultured lactic acid bacteria and making sure that the optimum conditions are available.
106
What conditions inhibit or prevent malolactic conversion?
Temperature below 15°C (59°F), a low pH and moderate levels of SO2.
If winemakers want to ensure that it is less likely to happen, they can add the enzyme lysozyme, which kills lactic acid bacteria, or move any batch of wine going through malolactic conversion to another part of the winery to avoid the spread of lactic acid bacteria. Alternatively, lactic acid bacteria can be filtered out to avoid malolactic conversion taking place.
107
What are the outcomes of malolactic conversion?
* **Reduction in acidity and rise in pH** – This is because lactic acid is a weaker acid than malic acid. This may be desirable in overly acidic wines but not in wines that are already relatively low in acidity.
* **Some colour loss in red wines**
* **Greater microbial stability** – If the wine goes through malolactic conversion during or after alcoholic fermentation, this then prevents malolactic conversion from spontaneously happening later when it would be undesirable. However, in cases where the pH of the wine is high, raising the pH slightly makes the wine more vulnerable to spoilage organisms.
* **Modification of the flavour** – A slight loss of fruit character may occur with the addition of buttery notes (notably in white wine).
* The process will also **increase volatile acidity**.
108
Why do some winemakers choose to conduct malolactic conversion in barrels for both white and red wines rather than in larger batches in tanks?
The advantages are the ability to be able to stir the lees at the same time and promote better integration of the flavours.
This method does require more work.
109
Why might a winemaker prefer to promote malolactic conversion at the same time as alcoholic fermentation?
Some studies have shown that this can increase fruity characteristics (or alternatively reduces the loss of fruit character from the final wines) and shortens production times, saving money as wines can be finished and sold earlier.
110
What post-fermentation adjustments can be made?
* Acidity, PH and tannin
* Removal of alcohol
* Colour
111
What is MegaPurple?
A grape-derived colouring agent used to enhance colour intensity for high-volume red wines.
This is not permitted within the legislation of some regions (e.g. Ribera del Duero).
112
What is the most simplest method of removing alcohol from wine?
he simplest solution for marginal adjustment (where permitted) is to add water to the must. However, adding water also reduces the intensity of flavour.
