Wine

WINE MAKING

VITICULTURE:
The study or science of grapes and grape rowing

ENOLOGY: The study or science of wine and winemaking

– Grain  Beer ( 3-12 % alcohol )

– Fruit   Wine ( 11-15 % alcohol, 22% fortified”sherry,port” )

Definition of wine:

Produced by normal alcoholic fermentation of the juice of sound ripe grapes with or without added fortifying grape spirits or alcohol, but without other additions or without the addition or abstraction except as may occur in cellar treatment provided that the product may be ameliorated before during or after fermentation.

Historical background:

  • It is assumed to be consumed before the beginning of recorded history.

  •  Romans advanced the art of wine making.

  • The research of Louis Pasteur revolutionized the wine industry (1840- bacteria is detrimental to wine).

  • Dom Perignon discovered that (1679) when wine is fermented after bottling, the bubbles it creates will remain in the wine so, he is considered as founder of champagne.

Grapes: Vitis vinifera family (European): From Spain to
California 
Vitis lobrusca
family (American): New York, More acid, low sugar, slippy skin) 
Many species, many varieties, differs from year to year and differ due
to; 
Local soil and climate. For harvesting soluble
solids(S.S.) is checked. When
it reaches to highest value (18-21%).
I
t should  be picked immediately 

If the grapes have reached the state of full ripeness and are not harvested immediately, their constituents are concentrated owing to evaporation of water. The grapes become overripe and soft, as a result of which the sugar content increases

  • Further concentration… if the grapes are attacked by the fungus, Botrytis cinerea.

  • Early stage, it causes ‘grey rot,’ …. a deterioration in quality

  • Late stage, … ‘noble rot’ develops, …desirable

  • in special areas, e.g., for the production of Sauterne.( intense and complex flavor)

Ice Wine (Eiswein): 

Clusters frozen on vine after hard freeze, juice pressed from frozen grapes (sugar increased by freeze concentration)

Nature of Microbial Process: 

  • Sugars of grapes ( D-glucose, D-fructose) anaerobic fermentation( yeast)   

                         Alcohol + CO2 + byproducts

  • Yeast: Alcohol tolerance, rate of fermentation, completeness of sugar to ethanol conversion and proportion of desirable by products formation.

  •  Kloeckera apiculata and Candida pulchermia and stellata are naturally exist on the skin of grape and they produce ethanol up to 5 %. After this level Saccharomyces cerevisiae over grown the above microorganisms.

  • Now pure cultures of Saccharomyces cerevisiae var ellipsoideus and var vini are being used. 1% of sugar is used to produce yeast cells, some of the alcohol is evaporated and some alcohol is entrained in CO2 and lost. Normally, ‘spontaneous fermentation’ can scarcely produce more than 17.5% by volume in a wine.

By product:

– Glycerol(2.5-3 %, accumulates during initial stages of fermentation.), One of the most important fermentation by product, which is a major contributory factor in forming the body of the wine.

– acetic acid ( 0.05-0.65 %, produced during early stages of fermentation),

– acetaldehyde ( 0.01-0.04 %, some converted to acetoin and than to 2,3-butanediol ),

– 2.3-butanediol (0.06-0.1 %),

– succinic acid (0.02-0.05 % )

– Higher alcohols (0.01-0.04 %).

– Level of all of these products is strongly influenced by yeast strain and environmental conditions, especially temperature.

Desired properties of a wine yeast;

– should produce alcohol up to 18 %

– should produce 8-12 % alcohol in a reasonable time at low temperatures ( i.e. 4-10 C)

at reasonably high sulfur concentration ( at low rH, redo potential ,it should be able to grow)

– rH = 0 reduction potential of H ion of 1 atm gas hydrogen 

– rH = 42 oxidation potential of oxygen ion of 1 atm oxygen gas

– rH > 25    oxidation

– 15 < rH < 25 medium range

– rH < 15 reduction

– most suitable range for fermentation           is 9 < rH < 15

– 20 < rH < 25 respiration of yeast

–  rH < 9 and rH > 25 inhibits the growth of yeast

– when there is 8-12 % alcohol in the broth, it should re start producing alcohol when extra sugar is added

– should be able to grow on 30 % sugar solution (osmophilic yeast)

– In southern parts of Turkey, yeast should be resistant to alcohol at high temperatures (30-32 C). (when temperature increases, alcohol inhibition increases

Effect of temperature on wine fermentation      

– Alcohol yield, rate of fermentation, concentration and proportions of by products, flavor compound formation  = f ( temperature of fermentation)

– More flavor (aromatic)compound is formed in wine by long, slow, low temperature fermentation than by a rapid, fermentation at temperature close to maximum temperature 

White wines are typically fermented at cooler temperatures than red wines. Cool temperatures (about 15 °C) enhance the production and retention of ‘fruit’ esters synthesized by yeasts, giving the wine a fruity fragrance. This is particularly important for white wines produced from cultivars with little distinctive aroma. Red wines often are fermented at warm
(about 22–25 °C) temperatures to facilitate yeast growth in the presence of grape phenolics, and to promote pigment and flavor extraction from the skins

  • 1 mole glucose, alcohol and CO2     DG= – 56 kcal  ( free energy loss)

  • 2 ATP (14 Kcal) is recovered and remaining is lost as heat. ( 75 % of the energy is lost as heat)

  • Large fermentation tanks cooling is required to keep the temperature constant.

Use of sulfur dioxide;

– Disinfect containers

– Control contamination by m.o.’s. Besides binding to m.o.’s and causing their death (by inhibiting metabolic enzymes containing S-H groups) it also combines readily with carbonyl compounds (i.e. acetaldehyde), unsaturated aliphatic compounds and proteins of the must. Combined form of the sulfur dioxide is much less toxic to m.o.’s and less effective as antioxidant

– protect wine against excessive oxidation during storage and aging (inactivates polyphenoloxidase enzyme so it prevents darkening of wine color

– Small amount of wine potassium bisulfate can be added as SO2 source.

– Large tanks pressurized SO2 is used.

– If acidity of must is high, required amount of SO2 decreases

– Elemental sulfur reduced to hydrogen sulfide and then it reacts with acetaldehyde to form mercaptoethanol which imparts objectionable flavor to wine even at very low levels.( to remove low levels of hydrogen sulfide aerate wine, to remove high levels of hydrogen sulfide treat with SO2 to oxidize hydrogen sulfide to sulfur.)

Yeast nutrition

Yeast needs carbon and energy source, nitrogen, vitamins, minerals. Some times nitrogenous compounds are limited. So addition of ammonium salts (ie (NH4)2HPO4) to sluggish growing yeast can be helpful. Especially it is good to add to inoculums. Wine yeast can ferment hexose sugars but not the pentose sugars

– Self digestion of yeast cells (autolysis, break down of cells) release amino acids and nucleotides so this impart undesirable flavor to wine.

– Autolysis is function of temperature and strain of yeast. Also these released compounds are good food for spoilage bacteria (lactic acid bacteria) therefore sediment yeast should be removed as soon as fermentation is completed.

– But for some cases where high acid wine is desired we may want to have autolysis intentially to support malolactic fermentation

De-acidification of wine

– Organic acids affect the sensory properties of wines, particularly tartness.

– Tartaric and L-malic acids are the major acids in grapes, the former being quantitatively the most important.

– However, grapes grown in cool regions, sometimes contain high levels of L-malic acid, leading to an excessive titratible acidity in the wine produced

Two methods to reduce L-malic acid:

The conversion of malic acid (a dicarboxylic acid) to lactic acid (a mono carboxylic acid) and CO2 during the fermentation is called bacterial malolactic fermentation. Lactobacillus, Pediococcus, Leuconostoc can cause malolactic fermentation. Autolysed yeast will support their growth. The malolactic fermentation most commonly occurs during the middle to late stages of alcoholic fermentation.

– Using certain yeasts (Saccharomyces pombe, malide varans) to convert L-malate to ethanol and CO2 in a mixed fermentation with a strain of wine yeast.

– Some times chemical reduction of acidity using calcium carbonate is also used. This treatment primarily reduces the level of tartaric acid by precipitation as the calcium salt

MAIN
STEPS OF WINE MAKING
 

1) Stemming and crushing: The first operation following the harvesting and transportation of the grapes to the winery is stemming and crushing. ….

– Revolving rollers (Garolla crusher).

– The crushed grapes are then separated from the stems as the grapes pass through a revolving drum perforated with holes which retain stems.

– The resulting crushed grapes ( including seeds and skins)  are then collectively termed as “ grape must” or just “must”

2) Addition of sulfur dioxide:

Added immediately after crushing to inhibit the growth of undesirable yeast and bacteria (50-100 ppm SO2 added). Since 57 % of sulfur is used to produce active SO2 from K2S2O5, conversion should be included in calculations.

3) Addition of sugar : Grapes may not reach their optimum maturity every year. ….. , sugar must be added to the must in order that wine will attain the proper alcohol content.

If grapes contain less than 22 % sugar an appropriate amount of sugar (refined sucrose) is added to bring the must to 22 Brix.

The following formula is used to calculate the amount of sugar to be added to yield a gape must of 22 Brix.

Ws = Wa ( B-A) / (100 –B)   where;

A: Brix of fresh must

B:  Brix of desired must

Wa: weight of the must

Ws: weight of the sugar to be added

Saccharose (sucrose) added to low-sugar musts is likewise fermented  owing to the high content of β-fructofuranosidase (invertase) in yeasts.

4) Color extraction:

– To produce white wine you may use green grape or red grape but be sure that use “cold press” to prevent color extraction from skins.

– To produce red wine you must use red grape and you should apply “hot press” or “fermentation on the skin” processes.

Fermentation on the skin :

Must together with grape skins will be going through alcoholic fermentation and alcohol produced will extract red anthocyanin pigments brings into the solution. The skins tend to float on
the surface of juice and reduce the contact of the skins with fermenting juice.

– The traditional method of securing contact has been to push skins down in to the fermenting liquid.

– In large containers this is very difficult and at present the liquid is pumped from the bottom of the container over the skins.

– When grapes contain mold, a number of polyphenoloxidase enzymes may be present. These cause oxidation of the red anthocyanin pigments to compounds with a brown color.

–  To prevent this there is an increasing practice of heating red grapes to inactivate the enzymes before fermentation. Heating also helps to release the color from the skins

Hot press:

It is often used in making red table wines. The must is heated to 62-63 C, pressed while hot, and then cooled immediately to room temperature. The high temperature of hot pressing extracts the pigments as efficiently as “fermentation on the skin” but some wine makers feel it results in an inferior wine due to undesirable chemical changes and loss of volatiles during the heating process.

Rose’ wine: limited color extraction or mixing red and white wine must

5) Amelioration:

– Adjustment of the must to the right quality before the fermentation.

– In some areas of the world (such as Eastern U S) wine grapes may not always reach maturity before harvest; hence, the grapes may be too acidic. To make quality table wines. (normal acidity ,0.7-0.9 g/100 ml, PH=3.6 )

The most common commercial method to overcome high acidity is amelioration the dilution of the wine by adding water and sugar.

A convenient method of amelioration is to add water in the form 22 brix sugar (sucrose) solution.

Amelioration is not legal in California and in some areas of Europe. (added sugar – water solution can be maximum 35 % of the total)

6) Fermentation: (secondary for red, first for white wine)

– Must is pumped into large fermenting vats (called cooperage). It is a closed vessel where CO2 exit is allowed but not the air in to the vessel.

– It is inoculated with wine yeast and grape sugar is converted to equal parts of alcohol and CO2.

– Complete fermentation, which converts the grape sugar and makes the wine “dry”, takes from a few days to a few weeks.

– Not all the wines are allowed to ferment completely. When some sweetness is desired, the fermentation is stopped while the desired amount of residual grape sugar remains unfermented.

– The temperature must never be allowed to become warmer than 30 C, because higher temperatures cause wine to loose fragrance and tend to stop the fermentation.

– Optimum temperatures for red wine are approximately 15-20 C.

– White wine benefits from a long, cool fermentation which retains the fruity, youthful flavors of the grape.

– So optimum temperature for white wines is 13-18 C.

– During fermentation, SS content of must will decrease first and then stabilizes. (That is the point where all the fermentable sugars are depleted.)

There are three ways of stopping fermentation:

– Racking (siphoning wine without disturbing the yeast which is collected at the bottom) most common one.

After a wine fermented to dryness, it is removed from the lees (dead yeast cells and insoluble material settled to the bottom of the cooperage). By pumping or siphoning the wine to different cooperage. Table wines are racked 2-3 times during production. (Once at the dryness, for tartarate removal and after finning before filtration) For tartarate removal wine is chilled to 0-2 C (4-10 days) to crystallize tartaric acid. And to precipitate it then it is racked to remove tartaric acid crystals.

– Adding alcohol (increasing alcohol concentration over 15 % will prevent yeast growth)

– Pasteurization by heat (not preferred due to excessive flavor loss)

7) Finning and clarification:

– Finning is the clarification of wine by the addition of a substance which reacts the tannins or proteins of the wine or some other added substance to yield a heavy, quick-settling coagulum.

– The finning agent also adsorbs suspended or colloidal material in the wine and, therefore exerts a clarifying action as the precipitate “settles out” of the wine. Agents used; Gelatin -tannin,-casein,-bentonite clay from volcanic ash deposition), -polyclar AT

Pectic enzymes are also used as clarifying agent. Catalyze the chemical breakdown of the pectin’s in wine.

– This pectin’s act as protective colloids holding other constituents in suspension in the wine, giving the wine a cloudy appearance when the enzyme “break down” these pectin’s a clarifying action is achieved.

– In most cases, Pectic enzymes are used while the grapes are “fermented on the skin”, because higher yields during processing can be achieved

– by adding a precisely determined amount of potassium ferrocyanide a series of other metal ions, such as those of copper, zinc, manganese, nickel, and silver, and the extremely toxic metal ions of lead and cadmium, could be precipitated out as
ferrocyanide complexes.

– Whereas centrifugation is only suitable for separating out relatively coarse trub particles, filters can remove even particles down to the molecular range from the wine.

8) Aging

– After filtration, aging generally begins in relatively large upright tanks, which are usually made of stainless steel, redwood or similar neutral materials.

– Another important duty is to keep each cask or barrel filled to the brim. Wine, especially table wine; is perishable and can turn into vinegar when in contact with air. The addition of wine to replace the wine loss by evaporation is called “topping” or “topping up”.

– During aging, wine develops smoothness, mellowness and character.

– The wine clarifies itself, some oxidation occurs as the wine “breathes” through the wood casks and the many complexes natural elements of wine slowly interact, or “marry” for smoothness.

– White seldom require aging more than 6-12 months.

– Red wines mostly aged up to two years.

– As wine mature, many producers complete the aging in smaller containers. Oak is favored by some, but red wood is also much in use. Casks of 1000 gallons, oval-shaped to make the lees deposit in a small space at the bottom, are preferred by many.

– The smaller the container of wood, the greater the ratio of surface through which the wine can “breathe” and take on the flavor characteristics of the container.

9) Blending wines for uniformity:

Many consumers want the same taste, color and fragrance in each bottle under a particular label. However, such uniformity is difficult to guarantee in a product so volatile as wine, because sunshine and moisture vary from year to year and so the grapes from each vineyard vary annually.

There are different times to blend:

a) Blending different grapes while they are being crushed.

b) Young wines are blended soon after fermentation.

c) Many wines of varying ages are blended after they are mature.

10) Bottling wine:

– Bottling occurs when the wine has improved in storage to the level called “ripe for bottling”.

– If wine remains in wooden cooperage too long, it may take on an excessively woody flavor, loose character or especially with white wines, become over-oxidized.

– Wine is only beverage that continues to improve after bottling.

  • Bottle-aging contributes as much improvements in some individual wines as cask aging does before bottling.

  • Closure for wine bottles is corks, screw caps or combinations of both. Metal caps should have inner seals to provide tighter closing and to avoid chemical action of the wine upon the caps.

Seals or capsules are normally wrapped around the necks and mouths of wine bottles to close off leakage, discourage tempering and refilling and to enhance appearance.

Wine quality:

“Why does one bottle of wine cost twice as much as another same sized bottle of the same type of wine?”

– More expensive bottle costs much more to produce, age bottle, ship and sell and that enough consumer exists who appreciate the wine well enough to pay the extra price.

– The grapes used maybe rare, delicate, hard to handle and expensive.

– The wine may have been aged for many years in small casks to develop complexity or there might have been a small quantity of the particular wine and a large enough demand for it to account for its price.

– No other factor of wine quality is so misunderstood as age. Age by itself is an unreliable guide to quality. It should be judged by its other qualities first. If the other qualities please, the age is less important.

– Vintage year (the year grapes grown ) is very important for European wines because quality changes a lot year to year.

– Year, when the grapes fully mature, is important and wines produced in that year is important and expensive.

Classification of wines:

Classification of wines is done with respect to different properties of wines: some of these are as follows,

– Dry wine (no fermentable sugar left in wine)

– Sweet wine (some fermentable sugars exist in wine, either left or added after fermentation)

– Fortified wine (alcohol added)

– Unfortified (all alcohol from fermentation)

– Sparkling wine (fermented in the bottle)

– Still wine (fermentation is completed before bottling)

– Red wine

– White wine

Evaluation of wines

a) Sensory examination: It is an important aspect of cellar operation. At least one person should be responsible in evaluating the data. Wines are judged by the following criteria

– appearance ( clarity, and freedom from sediments )

– odor, aroma, bouquet

– Taste ( sourness, sweetness, bitterness, astringency caused by tannins)

– Flavor ( overall impression)

Sensory evaluation is important for determining when wine is ready for bottling or shipment.

b) Microbiological examination: This includes both microscopic inspection and plating. Its main purpose is to detect excessive numbers of spoilage bacteria and wild yeast.

A sample of wine is plated on the agar plate containing 100 mg/l cycloheximide. It is an antibiotic which inhibits wine yeast but not the wild yeast. So observation of growth on this plate will be indication of wild yeast contamination.

Wine Spoilage

Due to existence of oxygen:

1) Ethanol to acetic acid (by acetic acid bacteria)

It will oxidize the color of wine (white wine amber color, red wine lawny brown color) flavor will also change (ethanol acetaldehyde)

2) Microbial spoilage:  Look at handouts

Carbonic Maceration

– The process of filling a vat with uncrushed grapes, where the grapes at the bottom of the vat are gradually crushed under pressure from the top grapes.

– Juice is released from the bottom grapes and begins to ferment.

– This fermentation releases carbon dioxide, which causes the uncrushed top grapes to ferment within their skins.

– This process is commonly used with young fruity wines with low tannins such as Beaujolais Nouveau. 

SOME IMPORTANT TYPE OF WINES

1) Vermouth:

– Combination of wine, aromatic plants, sugar, sometimes grape must in limited quantities, and alcohol.

– Caramel is the only coloring substance authorized, and is used for red vermouths.

– It contains 15-20 % ethanol. Has two types; Dry (<50 g sugar / l pale) and sweet (150 g sugar / liter dark).

– Most of it produced in Europe (essentially in Italy, France, and Spain)

Only neutral white wines that do not oxidize are employed; they must be low in tannin. The botanicals are usually incorporated into the vermouth in the form of an extract produced by macerating them in aqueous alcohol or a distillate obtained by distilling them in the presence of aqueous alcohol

2) Sherry:

– Most popular appetizer wine (15-20 % alcohol). Fortified with spirit.

– The wines with low total phenol contents suitable to spontaneously develop a wrinkly film of yeast (flor)on the surface of the wine.

– Development of flor depends on the temperature, and wines should be stored between 15 and 20 °C.

– The flor protects the wine from the uptake of oxygen, and prevents oxidative browning, to which the wine is very susceptible.

– The fortification of the wines to 15.5% alcohol (by volume) inhibits film-forming acetic acid bacteria, which would spoil the wine.

– Characteristic nutty (almond) flavor is obtained by aging, 4-8 years, at worm temperatures with Saccharomyces beticus, S. montuliensis and S. rouxii).

Sparkling Wines

  • Sparkling wines are gassy beverages in which the carbon dioxide is found in a state of oversaturation (generally, 4–6 bar at 20 °C).

  • When the wine is poured into a glass, CO2 is rapidly released as a result of the difference in pressure between the hermetically sealed bottle and atmospheric pressure.

  • The endogenous or exogenous origin of the CO2 allows these wines to be classified into two large groups: natural sparkling wines (those produced by the Champenoise, Charmat method (or similar methods), or the ‘pearl’ wines, which have a natural ‘sparkle’) and those carbonated artificially (aerated sparkling wines).

Champagne (sparkling wine):  

Generally pale gold or straw colored.

Classified due to residual sugar content;

Brut nature < 3 g l−1 (only residual sugars),

Extra brut 0–6 g l−1,

Brut < 15 g l−1,

Extra dry 12–20 g l−1,

Dry 17–35 g l−1,

Medium dry 33–50 g l−1, and

Sweet > 50 g l−1

Champagne begins as a white table wine usually several months old, and often made grapes specially grown and selected for it. This wine is blended carefully for fragrance, tartness and consistent quality (At this point it is called cuvee’).

Champagne yeast and sugar are added to cuvee’.
 This induces a second fermentation. At this point the wine is placed in to the bottles which are closed securely to withstand developing pressure caused by fermentation and to capture the CO2 gas produced. It develops more pressure than artificially carbonated soft drinks ever have 100 psia at the end. (Secondary fermentation, 5-6 weeks, 11-12 C, and then one year aging).

– After fermentation, the bottles may be transferred to a different site, for maturation at about 10°C.

– Maturation lasts for 12 months; during this period, the number of viable yeast cells drops rapidly, falling below about 106 cells ml−1 after 80 days.

– Thiamin and diammonium hydrogen phosphate, (NH4)2HPO4, are often added to the cuvée, in concentrations of 0.5 mg l−1 and 100 mg l−1 respectively.

– Thiamin appears to counteract the alcohol-induced inhibition of the uptake of sugar by yeast cells.

– 0.1% SS corresponds to 5 psia. If you want to produce pressure of 100 psia and if the wine contains 2.1 % SS, you should increase it to 4.1 % SS by adding sugar.

– Sparkling wines require such thick heavy bottles , wired-on corks. Workers sometimes wear face masks and gloves.

– Bottles of fermenting champagne are stacked in horizontal tiers or large boxes for few months to several years. During this time secondary fermentation occurs.

– After its completion, the wine ages in the bottles and on the yeast , until  the flavor and bouquet are perfected

Champenoise
,
individual bottle process:  (  Labeled as “fermented in this bottle)

– The bottles are placed upside down on racks. Each day the bottles are lifted slightly, twisted and turned, sediment has moved into the neck of the bottles (riddling process).

– The mouth of the bottles is plunged into a freezing solution of ethylene glycol (45%)  or brine solution, freezing the wine and sediment in the neck.

– When the crown cap is removed, the ice plug with the frozen sediment shoots out of the bottle due to the CO2 pressure. Pressure loss is approximately 1 bar, and wine loss is 10–15 ml (disgorging process).

– To compensate for the wine lost in this disgorging process, clear champagne and the dosage (which consist of a little sweet syrup and aged wine) are added.

– Finally the bottles are corked, the corks wired on and the bottle labeled.

– The champagne undergoes a short final aging before shipment

Transfer System (labeled as fermented in the bottle):

– The wine is left in the bottle with only a crown cap during a minimum of 9 months, sometimes more.

– It is then transferred under pressure with the lees to the Charmat tank.

– From this moment on, the process is exactly like that of the Charmat method.

– It is as laborious as the Champenoise method (from bottle to tank to bottle), and that filtration is carried out on a product that contains a Champenoise bouquet, significantly reducing the sensorial qualities of the sparkling wine.

– The contents of the bottle are disgorged under pressure into a tank.

– The yeast sediment is removed when the champagne is filtered under pressure through a filter into a clean bottle.

– The dosage is added to the tanks or to the bottles before filling.

– A short final aging follows before shipment.

Charmat, Granvas or bulk method;

– Fermentation occur in Charmat tank.

– Base wine and tirage ( nutrient, sugar and yeast) added.

– The ideal temperature for fermentation is 12–13 °C.

–  When the desired CO2 pressure has been reached (approximately 4 bar), the temperature of the Charmat tank is reduced to 8 °C to arrest the fermentation (with 10% of residual sugars).

– The low temperature causes the suspended yeast to sink to the bottom.

– Filtration ( to another tank) by counter-pressure uses a gas (usually carbon dioxide)

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