General Winemaking Options Flashcards
How can the effect of oxygen on ‘wine’ or ‘must’ be limited?
Avoiding ullage in vessels. 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.
Use of ‘inert’ 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.
Addition of sulfur dioxide.
Use of impermeable containers. Stainless steel and thick concrete vessels are impermeable to oxygen, whereas wooden vessels allow gentle ingress of oxygen. The use of glass bottles with screwcap can also minimise exposure to oxygen during storage in bottle.
Cool, constant temperatures. Cool temperatures slow the rate of oxidation reactions; hence the reason for maturing wines in relatively cool cellars or picking grapes early in the morning so that the fruit is not warm.
How can oxygen exposure be increased during fermentation and ageing?
Use of cap management techniques in red wine fermentation that spray or splash the must/wine
Use of small wooden barrels that can only contain a small volume of wine relative to the ingress of oxygen through the bung holes and staves.
Increasing the number 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
Use of techniques that involve pumping oxygen through the must (e.g. hyperoxidation) or wine (e.g. micro-oxygenation).
Explain Sulfur Dioxide as an Anti-Oxidant and as an Anti-Microbial preservative?
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.
What are the three forms SO2 have in wine or must?
When SO2 is added to must or wine, it dissolves and some of it reacts with compounds in the liquid. This proportion is called ‘bound SO2’ and it is ineffective 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.
Which form of SO2 in wine or must has the most effectiveness as an anti-oxidant/anti-microbial? How does pH levels effect this?
When SO2 is added to must or wine, it dissolves and some of it reacts with compounds in the liquid. This proportion is called ‘bound SO2’ and it is ineffective 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. 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
What practices does enrichment refer to?
Adding of dry sugar (cane or beet sugar, also known as chaptalisation) RCGM (rectified concentrated grape must) Grape must, grape concentrate. Either before or during fermentation to increase the alcoholic content of the final wine.
Give two examples of the coolest and warmest regions in Europe with regards to allowed enrichment?
Coolest zones include Germany (excluding Baden) and the UK. They must show a minimum of 8% natty potential alcohol and can enrich by 3% leading to a maximum alcohol level in the final wine of 11.5% (12% in red wine)
The warmest zones include most of Portugal, southern Spain, southern Italy, Greece. They must show a minimum natty potential alcohol of 9% and can enrich by 1.5% with a maximum alcohol level in final wine of 13.5%
How can sugar levels in Grape Must be concentrated using technology?
Reverse Osmosis, vacuum extraction and chilling.
Removing water: reverse osmosis, vacuum evaporation or cryoextraction (freezing the must, or even the final wine, and removing ice from it). The first two of these options are expensive because of the initial outlay on the machines used and therefore are limited to wines that will have a high return or wineries that produce high volumes of wine. Cryoextraction tends to cost less and so may be used more widely. In all cases, the costs must take into account that after these concentration processes there will be less wine to sell.
How can potential alcohol be lowered and what is the flow on effect of this?
By adding water to the grape must. This is only legal within some countries or regions (e.g. in California water may be used within the addition of other wine processing additives). However, adding water also dilutes the grapes’ aromas/flavours and acids.
Why do winemakers consider acidification?
In warm climates without any cooling influences, the malic acid in grapes tends to drop dramatically as the grapes ripen. If the wine is not acidified, it could lack freshness. Acidification can also be used to lower pH. Acidification is routine in most warmer parts of the world for inexpensive and mid-priced wines and many premium wines.
How do you carry out acidification?
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). 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. However, total acidity and pH are affected during the various winemaking processes, including malolactic conversion (if allowed to occur) and tartrate stabilisation. Therefore, the winemaker must take this into account when deciding the amount of acid to add.
When would you carry out de-acidification and how?
In cool climates where grapes may have to be picked before they are fully ripe (e.g. due to the threat of poor weather), it may be necessary to deacidify the must or 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. Deacidification is carried out by adding calcium carbonate (chalk) or potassium carbonate, and it lowers acidity by the formation and precipitation of tartrates. A high-tech option is deacidification by ion exchange. This last option requires considerable investment or hiring expensive machinery.
Explain pressing
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.
How does Pneumatic pressing work?
Also called ‘air bag presses’. 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. 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. Pneumatic presses are common in wine regions around the world in medium to large-scale wineries that can afford the initial investment.
How does basket pressing work?
Also called ‘vertical presses’ or ‘champagne presses’. 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. Some winemakers believe these to be gentler than pneumatic presses. However, they generally hold a smaller press load, are much more labour intensive and are therefore most suited to small wineries making premium wines.
