Grape wine is perhaps the most common fruit juice alcohol. Because of the commercialisation of the product for industry, the process is well known and documented.
The production of grape wine is quite straight forward and can be carried out at the small-scale, without the need for very expensive or specialised equipment. It does, however, require a basic understanding of the processes involved, tightly controlled fermentation conditions to ensure a high quality product and a strict adherence to cleanliness and hygiene to prevent contamination of the wine by spoilage bacteria.
Essentially, wine production involves the following basic steps;
- crushing the grapes to extract the juice
- alcoholic fermentation
- bulk storage and maturation of the wine in a cellar
- clarification and packaging.
There are really two distinctive types of wine made from grapes – red wine and white wine. The main difference in the two types is the variety of grape used as raw material and the removal of grape skins in the production of white wine. Grapes contain a number of chemical compounds that all contribute to the flavour and colour of wine. Tannins are one group of compounds that give the wine a bitterness and astringency. The tannins are found in the grape skins, therefore red wines tend to be more astringent than white wines.
Ingredients[edit | edit source]
Grapes Sugar Wine yeast Boiled water
Equipment needed[edit | edit source]
Large plastic bucket with a lid Thermometer Fermentation vessel that can be closed with an air lock Funnel Syphon tube Sterilising solution (sodium metabisulphite) Wine bottles and corks Corking machine Hydrometer (optional)
Principles of wine making[edit | edit source]
Wine making uses the following basic principles:
- The sugars present in the fruit (and any sugar that is added to the fruit) are fermented by yeast that is added to the mixture. There are natural yeasts present on the skins of fruits, but these are usually not sufficient to carry out the fermentation on their own.
- When sugar is fermented by yeast, it is converted into alcohol (ethanol) and carbon dioxide gas is released. You will see bubbles of carbon dioxide gas in the air lock while the fermentation is active. You know the fermentation is over when no more gas is produced.
- The fermentation has to take place without oxygen (it is an anaerobic fermentation). If oxygen gets into the system during the fermentation, the alcohol will be converted into acid (this is what happens when you make vinegar, which is acetic acid). Wine that has spoiled because it has been exposed to the air may taste very acidic.
- There are lots of bacteria and yeasts around in the air and on the surface of the fruits. They all have the potential to spoil the wine. It is extremely important that these bacteria do not start to grow in the fermenting grape juice. Particular care must be taken with the cleanliness of the equipment and personal hygiene.
- All equipment must be sterilised with a solution of sodium or potassium metabisulphite before it is used.
Production of red grape wine[edit | edit source]
Red grape wine is an alcoholic fruit drink of between 10 and 14% alcoholic strength that is made from the fruit of the grape plant (Vitis vinifera). The colour ranges from a light red to a deep dark red depending on the grape variety and the length of fermentation and maturation. There are many varieties of grape used including Cabernet Sauvignon, Grenache, Nebbiolo, Pinot Noir, and Torrontes. The skins of the grape are included in the production of red wine, to allow for the extraction of colour and tannins, which contribute to the flavour.
Production of white grape wine[edit | edit source]
White grape wine is an alcoholic fruit drink of between 10 and 14% alcoholic strength that is made from the fruit of the grape plant (Vitis vinifera).. The grape varieties used for making white wine include the following: Airen, Chardonnay, Palomino, Sauvignon Blanc and Ugni Blanc. White wine has a pale yellow colour. The skins are removed from the grapes before fermentation begins.
The fermentation process is very similar for both types of wine:
Raw material preparation[edit | edit source]
Select healthy, ripe, undamaged grapes. The fruit should taste sweet, ripe and slightly tart. Make sure they are ripe by squashing two handfuls, straining the juice and measuring the sugar level with a refractometer if you have one available. The total soluble sugars should be about 22° Brix, which is equivalent to a specific gravity of 1.0982 or 11% potential alcohol. Remove the grapes from the stems (stems make the wine taste bitter). Discard any that are rotten or unripe. Wash them well in clean water to remove dust. Crush the grapes to yield the juice plus skins, which is known as must. Traditionally grapes are crushed in large open vessels by people walking on them with bare feet. This really is not very hygienic and is not recommended. It is preferable to use a sterilised potato masher or very clean hands.
Sterilise the equipment[edit | edit source]
It is essential to sterilise all the equipment before use. Wash the equipment in boiling water. Use a solution of sodium or potassium metabisulphite to clean the fermentation vessel and the bottles for storage. Add 3 tablespoons of potassium metabisulphite to 4.5 litres of water and mix well. Rinse the bottles well with boiled water afterwards to get rid of any residual sulphite.
Processing[edit | edit source]
Red wine
Transfer the crushed grapes plus skins to a large fermentation vessel, such as a plastic bucket with a lid. Seal the lid, place in a warm room (21-24°C) and leave to ferment for between 24 hours and three weeks. The ethanol produced during this initial fermentation helps with the extraction of pigment from the skins. The longer the fermentation, the darker the wine.
Remove the skins and transfer the partially fermented wine to a separate tank to complete the fermentation. Add yeast to the fermenting grape must, close the top of the fermentation vessel with an airlock that contains water, place in a warm place (21-24°C) and leave to ferment until all the sugar has been converted to alcohol or the alcohol content of the wine has reached a high enough level. You know this has happened when the bubbles stop appearing in the water in the air lock. You can measure the specific gravity of the wine with a hydrometer. This gives an indication of the amount of alcohol that is present.
White wine
Strain the extracted grape juice into a fermentation bucket. Add the wine yeast, seal the fermentation vessel and leave in a warm place (12-18°C) for 7 to 14 days to ferment. The low temperature and slow fermentation encourages the retention of volatile compounds which give the wine flavour.
Adjusting the Juice[edit | edit source]
Controlling the acidity, sugar content and temperature of the juice (must) are all critical to producing good quality wine. The acid content can be measured using a titration kit. The ideal acid content is 6 to 7 grams per litre for dry reds and 6.5 to 7.5 grams per litre for dry whites. If the acidity is to low, add tartaric acid (in very small amounts) until the acidity reaches the desired level.
The sugar level should be about 22° Brix for both red and white wines. If it is lower than this, increase it by adding a sugar syrup to the juice. Make the sugar syrup by dissolving one cup sugar into one-third cup of water. Bring it to a boil in a saucepan and immediately remove from the heat. Cool before adding in small amounts, one tablespoon at a time, until the desired degrees Brix is reached. To lower the sugar level, simply dilute the must or juice with water.
The temperature of the must should be adjusted to provide optimum conditions for the yeast to grow. The optimum temperature of the juice is about 22-24°C for red wines and 12-18°C for white wines. If the juice is colder than this, warm it by gentle heating, but do not boil as this affects the flavour of the wine.
Racking the Wine[edit | edit source]
"Racking" means transferring the fermenting wine away from the sediment at the bottom of the bucket. Use a clear plastic tube to siphon off the wine into a sterilised fermentation jug. Do not disturb the sediment at the base of the bucket – it is important to have a clear wine without cloudiness or debris. Seal the top of the fermentation jug with a sterilised bung and a fermentation airlock. Leave to ferment until no more carbon dioxide gas can be seen escaping via the air lock (this means that all the available sugar has been converted into alcohol, or the yeast has died and the fermentation is complete).
Bottling the Batch[edit | edit source]
After fermentation, the wine is bottled by siphoning it off into clean, sterilised bottles. Do not fill the bottles to the top (leave about 5cm of head space) to allow room for fermentation in the bottle if it happens. Insert a cork into the bottle using a hand corking machine.
Some wines can be drunk immediately, however most develop distinctive flavours and aromas by leaving them to age for a while. The bottles should be laid on their sides during ageing to keep the cork wet. If the cork dries out, it may allow air into the wine, which causes it to oxidise and spoil.
Flow diagram
Dry Red Table Wine
Ingredients (for 4.5l of wine) 9kg ripe red grapes 1 campden tablet (or 0.33g of potassium metabisulphite powder) Tartaric acid, if necessary Granulated sugar, if necessary 1 packet wine yeast (like Prise de Mousse or Montrachet)
- Harvest the grapes once they have reached 22-24 percent sugar (22- 24° Brix). Wash well to remove dust. Remove stalks.
- Sanitize all equipment by washing well with a solution of potassium metabisulphite (3tbs per 4.5 litres of water). Place the grape clusters into a nylon straining bag and place the bag into the bottom of the food-grade bucket. Using very clean hands or a sterilsed tool such as a potato masher, firmly crush the grapes inside the bag. Crush the campden tablet (or measure out 1 teaspoon of sulphite crystals) and sprinkle over the must in the nylon bag. This is to control the growth of natural yeasts and bacteria that may be present on the skins of the grapes. Cover the bucket with cheesecloth and let it sit for one hour.
- Measure the temperature of the must. It should be between 22-24°C. Take a sample of the juice in the bucket and measure the level of acid with a titration kit. If it's not between 6- 7 grams per litre then adjust with tartaric acid.
- Check the level of total sugars (° Brix or specific gravity) of the must. If should be about 22° Brix (1.0982 SG). If it is lower than this, add a little bit of sugar dissolved in water. If the °Brix is higher than this, dilute the must with boiled water until it is the correct concentration.
- Dissolve the yeast in 500ml warm (27-30°C) water and let it stand until bubbly (it should take no more than 10 minutes). When it is bubbling, pour the yeast solution directly onto the must inside the nylon bag. Agitate the bag up and down a few times to mix the yeast. Cover the bucket with cheesecloth, set in a warm place (20-25°C) and check that fermentation has begun in at least 24 hours. Monitor the temperature and the progression of the fermentation regularly. It may be necessary to wrap a blanket around the fermenting bucket to maintain the optimum temperature for fermentation. Keep the skins under the juice at all times and mix twice daily.
- Once the must has reached "dryness" (at least 0.5° Brix or 0.998 SG), lift the nylon straining bag out of the pail and squeeze any remaining liquid into the pail.
- Cover the pail loosely and let the wine settle for 24 hours. Rack off the sediment into a sanitized 4.5litre jug, topping up with a little boiled, cooled water to entirely fill the container. Fit with a sterilised bung and fermentation lock. Keep the container topped with grape juice or any dry red wine of a similar style. After 10 days, rack the wine into another sanitized 4.5litre jug. Top up with dry red wine of a similar style.
- After six months, siphon the clarified, settled wine off the sediment and into clean, sanitized bottles. Cork with the hand-corker.
- Store bottles in cool, dark place and wait at least six months before drinking.
10. Red wine is fermented with the pulp and skins. This "cap" will rise to the top, so you need to "punch it down" frequently with a sanitized utensil
References and further reading[edit | edit source]
- Small-scale Food Processing: A directory of equipment and methods, 2nd Edition. Azam-Ali, S, Judge, E, Fellows, P and Battcock, M (2003) ITDG Publications, London.
- Elaboración de Vino: Proyecto San Martín, A. Puerta, ITDG-Perú/CEPCO, 2000 (In Spanish)
- Vino de Frutas: serie procesamiento de alimentos 6, ITDG-Perú, 1998 (In Spanish)
- Toddy & Palm Wine, (Practical Action Technical Brief)
- Home Wine Making http://www.homewinemaking.co.uk/
Equipment suppliers[edit | edit source]
This is a selective list of suppliers of equipment and does not imply endorsement by Practical Action.
General suppliers of brewing equipment
Youngs Home Brew - Wholesale suppliers of brewing equipment Cross Street, Bradley Bilston. West Midlands WV14 8DL. United Kingdom Tel: + 44 (0) 1902 353352 Fax: + 44 (0) 1902 354852 Email: enquiries@youngshomebrew.co.uk http://www.youngshomebrew.co.uk/
EasyBrew 4 Enterprise Park 86 Parsonage Barn Lane Ringwood Hampshire BH24 1PZ Tel: 01425 479972 Fax: 01425 479972 Email: info@easybrew.co.uk Web Site: www.easybrew.co.uk
Brew it Yourself Unit 4 Parkside, Potters Way, Temple Farm, Southend On Sea, Essex. SS2 5SJ. Tel: +44 (0) 1702 614422 Email: orders@esuasion.co.uk http://www.brew-it-yourself.co.uk/
Refractometers and pH meters
Fisher Scientific UK Ltd Bishop Meadow Road Loughborough LE11 5RG UK Tel: +44 1509 231166 Fax: +44 1509 231893 Email: fisher@fisher.co.uk Web: www.fisher.co.uk
International Ripening Company 1185 Pnieridge Road Norfoplk Virginia 23502-2095 USA Tel: +1 757 855 3094 Fax: +1 757 855 4155 Email: info@QAsupplies.com Web: www.qasupplies.com
Gardners Corporation 158 Golf Links New Delhi 110003 India Tel: +91 11 23344287/23363640 Fax: +91 11 23717179
Practical Action The Schumacher Centre for Technology and Development Bourton-on-Dunsmore Rugby, Warwickshire, CV23 9QZ United Kingdom Tel: +44 (0)1926 634400 Fax: +44 (0)1926 634401 Email: inforserv@practicalaction.org.uk Website: http://www.practicalaction.org/
This document was produced by Dr. S Azam Ali for Practical Action in March 2008. Dr. S Azam-Ali is a consultant in food processing and nutrition with over 15 years experience of working with small-scale processors in developing countries.
