Wine
- 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.
| Color | Red(pigmented) White (not pigmented) |
| Sugar content | Sweet wine – some sugars are left during fermentation and recovery Dry wine- all sugars fermented into alcohol |
| Alcohol content | Table wine- 3-10% alcohol Fortified wine- 19-22% alcohol (since yeast cannot accumulate late alcohol, whisky is added) Dessert wine = Fortified sweet wine with 22% alcohol |
| Carbonation or CO2 content | Still wine: no CO2 is produced during fermentation. Sparkling wine: with CO2 production. E.g. champagne |
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= 22-27oC for 3-5 days
- White wine preparation= 10-21oC 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 50-60oC 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 15-20oC 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