Wine production using fruit juice

/Wine production using fruit juice
Wine production using fruit juice2018-06-06T16:04:52+00:00

Wine production using fruit juice

Wine production using fruit juice

Introduction

Wine is an alcoholic beverage, made of fermented fruit juice, usually from grapes. The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients. Grape wine is produced by fermenting crushed grapes using various types of yeast. Yeast consumes the sugars in the grapes and converts them into alcohol. Different varieties of grapes and strains of yeasts produce different types of wine. Wines made from other fruits, such as apples and berries, are normally named after the fruit from which they are produced (for example, apple wine orelderberry wine) and are generically called fruit wine or country wine. During fermentation, yeast interacts with sugars in the juice to create ethanol, commonly known as ethyl alcohol, and carbon dioxide (as a by-product). In winemaking, the temperature and speed of fermentation are important considerations as well as the levels of oxygen present in the must at the start of the fermentation. In winemaking, there are different processes that fall under the title of “Fermentation” but might not follow the same procedure commonly associated with wine fermentation.

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.

Principles of winemaking

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.
  • 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 sterilized with a solution of sodium or potassium metabisulphite before it is used

Requirements

  1. Reagents/Supplies
  2. Fruits (apple or grapes)
  3. Potassium metabisulphite
  4. S. cerevesiae culture

Procedure

Production of red grape wine

Red grape wine is an alcoholic fruit drink of between 10 and 14% alcoholic strength that is made from grapes. The colour ranges from a light red to a deep dark red depending on the grape variety and the length of fermentation and maturation. 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

White grape wine is an alcoholic fruit drink of between 10 and 14% alcoholic strength.  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

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

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 afterward to get rid of any residual sulphite.

Processing

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 airlock. 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

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 liter 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

“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 sterilized 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. 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

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 oxidize and spoil.

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