• Wine is a kind of undistilled alcoholic beverage mainly prepared from fruit juice. (mainly from grapes).
• The process of preparation of wine is known as vinification and the branch of science that deals with study of wine is known as enology (American) or oenology (British).
• There are different types of wine on different basis.
• Besides fruit and berries, non-toxic plants (flowers) etc can also be used for wine production.
• Since, basic constituent of wine is alcohol, other substrates are also added in it.
• It contains 3-22% of alcohol.

Microbiology: Grape juice (27% sugar) is fermented by various strains of Saccharomyces cerevisiae.

Wine production:

• Wine is basically the transformation of sugars of grapes of yeast under anaerobic condition into ethanol, CO₂ and small amounts of byproducts such as D-glucose.

What are the basic steps of wine making?

• Step I: Harvesting of fruits:
  • Appropriate variety of fruits and berries are harvested.
  • They must contain high amount of fermentable sugars.
  • Grapes usually contain 5-25% total soluble sugar (Total soluble sugar).
• Step II: Crushing and extraction:
  • Thus, obtained fruits are crushed and extracted mechanically.
  • This process releases juice and a little bit pigment.
  • The whole mass is known as Must.
  • For white wine preparation, the skin is removed. The harvested fruits are de-steamed for white wine preparation which is not required for red wine preparation.
  • In case of red wine, the steam gives vegetable aroma due to presence of 2 methoxy-3-isopropyl pyrazine.
  • Color is also extracted from steam.
  • In case of red wine, the Must should be fermented.
• Step III: Optimization:
  • The must is optimized for two parameters, TSS and pH.
  • The TSS is generally optimized between 17-22% and pH in between 3-4, depending on yeast strains to be used.
  • KNS (potassium metabisulphite) may or may not be added at this stage which is an antimicrobial compound against Acetobacter spp. and competitive yeast.
  • It also acts as anti-oxidant and antifungal agent.
• Step IV: Primary fermentation:
  • The optimized Must is inoculated with 2-10% of inoculum and fermentation is carried out under optimum temperature.
  • Red wine preparation= 22-27^oC for 3-5 days
  • White wine preparation= 10-21^oC for 7-14 days
  • During the fermentation, the content is mixed twice a day by punching the floating skin for proper aeration.
  • It also helps in color extraction.
  • This fermentation allows rapid multiplication of yeast cell as well as sugar fermentation to ethanol, when the TSS is decreased nearly about 9-10% then primary fermentation is terminated.
• Step V: Pressing:
  • The skin of must is taken out and pressed in order to release juice and alcohol.
  • The liquid is again transferred into tank.
  • In case of white wine, pressing is carried out before fermentation.
  • During pressing color of fruits and berries is extracted.
• Step VI: Heat and cold sterilization:
  • The main aim of this technique is to remove the tartarate crystals (wine diamonds or wine crystals).
  • In cold sterilization method, the fermented must is cooled to nearly freezing and kept for one to two weeks.
  • During this period, the crystals gets separated or stirred in the wall of fermenter and clear liquid is collected on secondary fermented tank.
  • In heat stabilization technique, it is gently heated in between 50-60^oC for an hour and kept overnight.
  • The proteins get decanted.
  • The clear contents are pumped out and remaining turbid substance adsorbed on to bentonite.
• Step VII: Secondary fermentation:
  • It is carried out in stainless steel or oak barrel or concrete tank lined with plastic.
  • The stabilized, sterilized wine is now kept at 15-20^oC for 3-6 months under strict anaerobic condition usually in case of sweet wine, the fermentation is terminated when sugar content is reduced to 4-6%.
  • During secondary fermentation, aroma is developed.
  • The aroma in wine is categorized into 3 types:
    • Primary aroma —-> contributed by fruits or berries
    • Secondary aroma —–> developed during secondary fermentation
    • Tertiary aroma ——-> developed during bottled ageing
  • The aroma compound may be volatile or non-volatile.
  • It is developed due to chemical reactions among acids (malic acid, citric acid etc), sugars, alcohols and phenolic compounds.
  • The main compound responsible for aroma is methoxyparazine , monoterpenes, nor-isoprenoids, thiols, esters etc. among which ester is the principal one.
  • Esters are produced by reaction between alcohols and acids which is very slow.
  • It takes nearly one year for secondary fermentation
  • Before secondary fermentation malo-lactic fermentation occurs.
  • Malic acid (sharp sour) —–Lactic acid bacteria (LAB)—-> Lactic acid
• Step VIII: Laboratory testing:
  • After secondary fermentation, certain laboratory tests are conducted which includes bricks reading, bricks pH, titrable acidity, residual sugars, free or available sulfur, total sulfur, volatile acidity and alcohol percentage.
• Step IX: Blending and fining:
  • It is the most crucial to produce good quality of wine giving special taste and aroma.
  • In blending process, spices, extracts of aromatic plants, essential oils, fruit juices and other things are added in appropriate proportion.
  • Blending is kept trade secret in winery (wine industry).
  • In fining process, tannins and microscopic particles are removed in order to make clear wine.
  • For this purpose, wine is treated with gelatin, potassium caseinate, egg albumin, lysozymes, skimmed milk powder etc. or it is filtered through membrane filter or diatomaceous earth cellulose filter.
  • Finally, wine is clarified in order to remove pectin which is achieved with the use of pectinase enzyme.
• Step X: Preservation:
  • Pasteurization technique and use of KMS (Potassium metabisulphite) are mainly used for preservation.
  • It kills sugar utilizing micro-organisms.
• Step XI: Bottling:
  • Finally, wine is aseptically filled in bottle and bottle is corked, which is usually made with oak.
  • Finally, the outside cork is sealed.
  • The bottled wine can be directly consumed or preserved.

Distillation of wine:

• These are the alcoholic beverages/drinks obtained by the distillation of wine or fermented cereals.
• It may be aged or unaged (i.e. the distilled liquor).
• Distilled liquor is commonly called spirits.
• They consist of more than 40% ethanol.
• There are various types of distilled liquor. The primary types are:
• Whisky (Barley and others) —-> aged
• Brandy (Wine distillation) —–> aged
• Rum (fermented molasses) —–> aged
• Vodka (fermented cereals) —–> not aged
• Gin (distillation of fermented cereals) —–> unaged but flavored

Wine production process

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