Introduction rapes are unique among fruits. Ripe, they con- Gitte i pein sat of acid so that when they ferment enough alcohol is produced to make a palatable wine that is protected against imminent spoilage. Other fruits do not possess the proper balance of these basic constituents. Hence, sugar, acid, or water, or sometimes a combination of then must be added prior to fermentation. Otherwise, inadequate or excessive alcohol may be formed, fermen- tations may stick, and the product could either be so acidic (tart) or 50 flat that it would taste unpleasant or insipid. Minor adjustments in sugar and acid content of vinifera grapes may sometimes be required, but nat often. On the other hand, other fruits almost always require additional steps in preparing and handling the raw ma- terial that donit apply to making grape wine. Hence, this publication is confined to grape wines. The two major kinds of grapes used in the produc- tion of grape wines are native American species of grapes, or hybrids thereof, and the European species or Vitis vinifera, A well known American grape species is Vitis labrusca; many varieties are cultivated in the eastern United States, especially in New York. Labrusca varieties include Concord, Delaware, Niagara, Catawba, and Ives Seedling, To varying degrees, these grapes and the wines made from them have a noticeable aroma, commonly referred to as “oxy,” that is partially due to the presence of the compound methyl anthranilate. Primarily, this characteristic distinguishes these wines from those pro- duced elsewhere, particularly in western Europe and California, Besides their distinct aroma, these native ‘grape varieties generally contain insufficient sugar to produce a balanced table wine. Thus, in eastern wine ‘making adding sugar or chaptilization is. permitted. These grapes also have other compositional and phys- ical characteristics that require specialized handling methods. Because of these factors, as well as the more extensive interest in vinifera wines, the making of wine from American grape species will not be covered here. However. for those interested in making wine from Amer- ican grapes, we highly recommend Grapes into Wine by P.M. Wagner (see Selected References) ‘Wine types are usually divided into classes accord- ing to their alcoholic content, groupings that form convenient basis for excise taxes upon alcohol. The two ‘major classes are table wines (9 t0 14 percent alcohol) and dessert and appetizer wines (15 to 21 percent alco- hol), Table wines owe their alcoholic content to the fermentation of sugar naturally present in the grapes and to the sugar that may be added to them. On the other hand, dessert wines obtain their higher alcoholic content from the addition of alcohol (wine spirits). De- mand for table wine in the US. far exceeds that for dessert wine and because demand for information on home wine making has centered on making table wine, this publication is about grape table wine only.Tax-free production of limited quantities of wine at home was allowed for many years in the United States, even during Prohibition. Despite this apparent legal free- dom, laws and regulations pertaining to home wine making contained several arbitrary restraints that led to confusion and inconvenience. In 1979, these regula- tions were liberalized to permit home wine making with- ut requiring registration. Details of the new regulations are given at the end of this publication. Although no published figures exist on the volume ‘of homemade wine produced in the US. annually, most observers agree that it probably exceeds 10 million gallons. Along with increased wine consumption since 1970, an “explosion” in the demand for information about grapes and wine has occurred in the United States Not only has California's grape and wine industry expe- rienced rapid growth, but a grape and wine growing renaissance has occurred in more than 40 other states as well. in California, the number of bonded wineries, mostly small table wine operations located primarily in coastal areas and the foothills, now total over 650. Many new winery entrepreneurs began their ventures as home winemakers In response to widespread interest, this guide cov- ers the fundamentals of making table wine that should provide the basis for more successes than failures. Mak: ing your own wine can be an enjoyable, enriching, and rewarding experience. The ability to consistently make sound, above average, quality wines requires not only the desire to succeed, but, at times, hard work, patience, and attention to detail, Aside from motivation and adherence to details, two other factors can influence the successful produc- tion of table wine at home: the amount to be produced and the kind of raw material used. While a few gallons of sound, palatable wine can be made easily from recan- stituted grape concentrate, producing a fine quality wine 1s more readily realized from larger lots, using fresh, ripe grapes. Successful production of just 5 to 10 gallons of wine from small quantities of grapes requires con- siderable technical skill, experience, and the proper equipment, owing to the larger surface-to-volume ratio inherent in small volumes. Working with larger quanti- ties of grapes and larger wine volumes minimizes chances of spoilage and oxidation. Thus, we recommend work- ing with a minimum of about ' ton of grapes to pro- duce about 50 gallons of finished wine. Although these guidelines are presented with these factors in mind, the principles covered apply equally to smaller wine mak- ing activities. As a matter of fact, many beginners may wish to start out with one or two 5- to 10-gallon fer- mentations of reconstituted grape concentrate to be- come familiar with alcoholic fermentation, the adding of yeast and sulfur dioxide, and other wine making steps.Acknowledgments a technologically sound, practical, and concise 31-page booklet to anyone seeking assistance on home wine making, particularly those using Vitis vinifera ‘grapes. That booklet, published in 1962, was Wine Make ing at Home by Maynard A. Amerine and George L. Marsh, and unfortunately itis now out of print and no longer available. This publication owes a great deal to that well written, useful work. We also acknowledge the following books as rich, technical resources: The Tech- nology of Wine Making: Table Wines, The Technology of Their Production: and Wine, An Introduction. They are listed in this guide under Selected References, along with other books, bulletins, and pamphlets ‘The authors also appreciate and recognize the ex- tensive knowledge they have gained over the years throtigh lectures and personal communication with the faculty of the Department of Viticulture and Enology. University of California, Davis, notably Professors Roger B Boulton, Ralph E. Kunkee, Cornelius S, Ough, Vernon L, Singleton, and A. Dinsmoor Webb. Finally, we are particularly indebted to Peter Brehm, John Daume, and Desmond Lundy for their insightful guidance regarding wine making equipment and supplies, and to the re- viewers of this publication for their time and helpful advice F ‘or many years, one of us (Cooke) recommended ivContents Introduction 1 Overview of Wine Making 3 Composition and Quality of Grapes and Wine 4 Making Red Table Wines 7 Crushing and stemming ‘Adding sulfur dioxide ‘Adding pure wine yeast starter cultures Alcoholic fermentation Pressing Malolactic fermentation ‘Completing alcoholic fermentation Racking ‘Aging and topping Bowling “Making rosé or pink table wines ‘Making White Table Wines 18 ‘Crushing, stemming, and pressing Adding sulfur dioxide, setting, adding yeast, and fermentation Racking, topping, aging, and bottling Potential Spoilage and Stability Problems 22 Acetification and oxidation Hydrogen sulfide (1:5) CCloudiness and deposits Other clarifying and fining agents Wine filtration Analyzing Juice and Wine 25 Wine acidity and pH Keeping records Soluble solids *Brix) Reducing sugar Tiratable acidity Toral and free sulfur dioxide Malic acid Evaluating Wine Quality 30 The Wine Making Facility 32 The processing work area “The wine aging and storage areas Equipment and supplies Cleaning and sanitizing Cleaning and maintaining of wooden cooperage Afterword 37 Helpful Sources and Information 38 Selected references Sources of equipment and supplies for home wine making Additional sources of information and assistance Federal regulations pertinent to home wine making, Glossary 42 ittOverview of Wine Making processing operations are common to making white and red table wines. However, they are not all performed in the same order: 1. Stemming and crushing, Stems are separated from ‘grape berries, the skins of which are broken to free the juice. The mixture of juice, skins, seeds, and pulp is called must 2. Determining sugar and acidity of the juice. Sugar content is approximately equal to percent soluble solids (° Brix) 3. Adding sulfur dioxide ($0,). Needed to inhibit ‘growth of spoilage organisms and prevent oxidation. 4. Adding pure wine yeast starter cultures. Facili- tates a clean, consistent, and complete fermentation, 5. Pressing, Skins and seeds are separated from the juice at the beginning in the case of white wine and after some fermentation on the skins in the case of red 6. Fermenting. Yeast converts sugar to alcohol and carbon dioxide. 7, Racking wine from lees. The clear wine is sep- arated from spent yeast cells and other solids after fermentation 8. Adjusting SO, content. Prevents spoilage and oxi- dation 9. Aging/topping and/or clarification. 10, Bottling. These 10 wine making steps may appear relatively easy to the experienced winemaker. The inexperienced winemaker, however, must learn to check details, such as topping in a timely manner, using a pure yeast wine starter culture, or properly using SO:, to avoid wine spoilage. For several reasons, good quality red table ‘wines are easier for the beginner to make than are white ‘wines, mostly because white wines are more subject to oxidation and browning, Therefore, start with red table vwines to gain experience The major difference between red and white wines is that, after stemming and crushing, the juice of the must for red wines is fermented on the skins for sev- eral days to extract their red pigments, In white wines, only the clear juice is fermented to minimize extraction of tannins from skins and seeds. Other significant Aifferences: 1. White wines should be fermented at cooler tempera- tures than are reds to achieve the best quality 2. Red wines gain in quality and complexity by aging in oak barrels, 3. White wines generally are made without wood aging and are consumed when they are relatively young: thus, they retain fresh and fruity aromas and flavors. For both red and white wines the volume of wine made must be larger than the toxal storage capacity of the aging or storage containers—glass carboys, gallon jugs, or barrels—because additional wine will be needed to replace the volume lost to lees after fermentation, and for topping during aging to replace wine lost to ullage or evaporation. (See sections on racking and aging of red wines.)2 Composition and Quality of Grapes and Wine naterials for wine: freshly picked grapes, grape juice concentrate, or frozen must or juice. Of the three, itis generally recognized that the first offers the greatest quality potential and the second offers the most convenience. Both red and white grape juice concen trate is available from most vendors of home wine mak- ing supplies and is readily reconstituted by diluting with water, Follow the suppliers’ directions to obtain juice of the desired strength. Varietal concentrate or the concentrated juice of different wine grape varieties is also available for home wine making, A few firms in California sell fresh frozen vinifera varietal grape must or juice. Limited evaluations suggest that wines made from frozen juice or must can be of acceptable quality when compared with wines made from fresh grapes, ‘The obvious advantage to making wines from reconsti- tuted grape concentrate or frozen must or juice is that they can be made at times other than the usual fll grape harvest T: home winemaker has a choice of three raw The best raw material: fresh grapes Fresh, ripe, varietal wine grapes remain the best raw material for making wine. Some home wine shops will accept orders for fresh varietal vinifera grapes be fore the harvest season, Home winemakers located near California's many coastal and foothill vineyards can pur- chase fresh wine grapes directly from a grower of from growers through wine grape grower associations, Grow ers can also be contacted through many University of California Cooperative Extension county farm advisor offices, A description of wine grape varieties, including, usual harvest period, may be found in UC Publication 4069 (see Selected References) Place orders and make arrangements for delivery or pickup 3 months in ad~ vance (usually in June) to insure getting the quantity of each varietal desired. 1n planning grape purchases, be aware that many growers who sell small quantities of grapes for home wine making pick into lug boxes that hold about 50pounds of grapes each. Thus, 1 ton of grapes will re ‘quire 40 boxes, Some growers may require a deposit for the lug boxes or you may have to provide your own picking containers, Make this arrangement at the time of your order; always return lug boxes clean and dry. large plastic tubs can be substituted for wooden boxes Depending upon the variety and other factors, the home winemaker can usually expect that 1 ton of grapes for ‘white wine will yield about 100 to 120 gallons of wine; 1 ton of red wine grapes will yield about 120 to 150 gallons of wine (the more press wine used, the higher the yield), Aside from the form of raw material itself, several ‘important factors influence wine quality. Foremost: Good ‘wines can only be made from good grapes Grape quali- ty is directly related to the composition of the fruit when itis harvested. in turn, grape composition is influ- enced by climate. Premium wine grape varieties, such as Chardonnay, White Riesling, Gewirztraminer, Pinot noir, and Cabernet Sauvignon, are obtained from the cooler north, central, and south coastal California counties. Many foothill vineyards, as in California's Amador and El Dorado counties, yield good quality Zinfandel, Sauvignon blanc, French Colombard, Chenin blanc, Petite Sirah, and Barbera. Extensive research concludes that climate is the single most important factor affecting the compo: sition and quality of California's wine grapes and hence the composition and quality of its wines. Specifically, in cooler climates, more grape acids, varietal grape aroma, and flavor compounds develop and, in the case of red Which variety to select? Dissinctiveness or intensity of grape aroma varies ‘widely between varietie of Vids vnera and within 4 variety depending upon climate ripeness of the grapes, cop size, and other factors. Below i a listing of some ‘wall known and imporant varieties grouped according, {o their potential intensity of veictal arom Distinctive white wine types. Muscat blane (Muscat Canlli, Muscat Frontignan Masa of Alexan Aria, Orange Museat, Symphony, White Ries Semillon, Emerald Rising, Gewarsvaminer, Syvaser, Geey Wing Pinot blane,Chenin ane Distinctive red wine types. Cabernet Seuvignon, Carmine, Barba, Cenarion, Pino ol (Gamay Bes jolais), Merlot, Nebbiolo, Zinfandel, Ruby Cabernet Grenache, Carnelian, Peat Seah (Dust), Napa Gamay Nondistinetive white wine types. Ali Burger. Thompson Seeds, Cslombard (Peach Colom td, Green Hungarian, Palomino | Nondistinctive red wine types. carignae } ‘Charbono, Emperor, Flame Tokay, Refoco, Table 1. Desired sugar aid Ont Wine type ‘gr ‘White wine grapes 20527" Brix’ Red wine grapes RSS" Brx 6-8 WL 3333 "Values expressed as g tartare acid per L. “8 measure of free hydrogen (acid) ions ina solution. "A measurement of soluble solids, roaghly equal to percent sugar content types, tannins and color are retained at higher, more desirable levels. These compounds are directly related to wine quality. Table I shows the amounts of certain ‘components of white and red wine grapes that are gen- erally considered to be desirable for good quality wines. Of interest to the winemaker are these major grape components: grape sugars, organic acids, aroma and flavor compounds, polyphenolic compounds or tannins, certain amino acids, and certain metallic ions, such as potassium. Fully mature or ripe grapes contain about aan equal concentration of glucose and fructose, which are the simple sugars yeast ferment to form alcohol and carbon dioxide. Ripe grapes contain from 70 to 80 per- cent water by weight. Depending upon the variety, the predominant or- ganic acids in grapes are tartaric and malic acids. In addition to their contribution to the flavor and balance of wine, tartaric acid is involved in wine stability, while malic acid is involved in the malolactic fermentation (see Glossary). The complex nature of grapes and wine has been verified by the isolation and identification of more than 400 aroma and flavor compounds present. Such polyphenolic compounds as tannins are also irn- portant to wine flavor, stability, and aging, particularly in red wines. Certain amino acids have been shown to influence wine quality. but they are pethaps more im- portant as a source of nitrogen for yeast cell metabo- lism, Such metallic ions as potassium are constituents important in wine quality and stability. Finally, while the individual and combined interactions and contribu- tions of these grape and wine components to wine qual- ity are complex, they become more understandable with study and experience. Because climate or other factors are unreliable, it is not always possible to obtain grapes with optimal sugar, acid, and pH. Fortunately, home winemakers are not hampered by both the federal and state regulations that control amelioration in commercial wine making. Sugar levels that exceed 25° Brix can be lowered by adding water, to avoid difficulty with fermentation. The fer- ‘mentation may even stop before dryness, resulting in incomplete fermentation. However, adding water to re- duce a must’s sugar content will also lower its acidity;such a change would be undesirable in a must already deficient in acidity. Thus, there are three options: 1, Ferment without adjustment. 2. Blend before fermentation with juice or must of the same variety that has moderate sugar and high acidity. 3. Before fermentation add water to lower sugar con- tent and raise acidity to taste immediately after fermentation, ‘A must seriously deficient in acidity may also require acid addition before fermentation, Selection of the most suitable action will vary according to each lot and the winemaker’s objectives Must or juice sugar and acid that fall well below levels shown in table I should be adjusted. A useful rule of thumb: To produce a wine of about 12 percent alco- hol. the must or juice should be between 22° to 24° Brix. Sugar is increased by adding cane or beet sugar (sucrose). Use the following formula to calculate the amount of sugar to add to increase the °Brix B-A sewx a@oo-8) where, S = weight of sugar to be added to increase must or juice to a desired ° Brix W = weight of grape must B = desired ° Brix A = original ° Brix of grape must For example, if you want to raise the °Brix of 10 pounds of juice or must from 15 to 23, calculate the amount of sugar required as: 22-15 s=10x = 108 100-25) It should be apparent that large amounts of 15° Brix juice requite proportionately larger quantities of sugat to raise the °Brix to the desired level. For exam- ple, 10.4 and 104 pounds of sugar would be needed to increase the °Brix from 15° to 23° with, respectively, 100 and 1,000 pounds of must or juice. Considering the high cost of sugar, riper grapes are obviously preferable. A ess accurate method for raising the sugar content by 1° Brix is to add 125 pounds sugar to each 10 salllons of juice o must. Deficiencies in total acidity can be corrected sim- ilarly. Table 2 gives the amounts in grams (g) of tartaric acid that must be added to each galion (gal) of must or juice to increase the titratable acidity (TA) from a given low level to either 6 or 8 g per liter (L). ATA of 6 g/L is, considered a minimal acid level and a TA of 8 g/L is optimal acidity, especially for white wine. For example, to increase the TA of a Zinfandel must from 5 10 6 g/L, 38 g (1.33 oz) tartatic acid are required for each 10 gal of ‘must. Metric units, such as grams, are readily converted to other units of measure using the adjacent Conversion Factors chart (table 3) Table 2. Amounts of artic acid required to increase acidity Toobain 60g ToabuinowL Present ac content ada to each gal: add to each gal: wt) © @ 30 n3 139 a5 94 170 40 15 152 6 36 132 50 38 ua 33 19 95 60 75 25 56 70 38 5 19 “Tivatable acidity a ara aid “Table 3. Conversion factors Toconveniom ‘To Maltiply by eres 04047 Cups 80 Caps lies 2366 Dams milters a7 Galloas ders 379 Grams raligeams 1090 Grams ounces 0.035 Cramster pounds/gal 9345x107 Hectares seres 2a Healers Tkers 100 Kilogram ‘ans 1000 Kilograms ounces as27 ilograms, pounds 2 Less ‘allons 0264 Liters oxnces 238 Liters pints 21 Les quarts 106 Miligrams ‘grams 001 Miigears ‘ounces 35X10 ‘learns pounds 22x 10°6 Miliizers| hers ‘001 aliers ounces 0034 Ounces grams 233 Ounces rniiers 2957 Pins gallon 0125 Pins ounces 6 Pounds ‘rams 4536 uns Tiers 0946 Tablespoors reaspoons 3 ‘Tabespoons| ounces os Tablespoons ralliiers 5 ‘Teaspoons stbvers 5 Teaspoons tablespoons 3 Following adjustmentsin sugar and/or acid content, the °Brix and/or TA should be determined again to ver. ify that the desited adjustment has been achieved,3 Making Red Table Wines igure 1 is a schematic of the basic operations Pes in maling rd able wines, Ech step is discussed below. Additional information, not depicted in the schematic drawing. is also presented Crushing and stemming This first step may be performed by hand or by machine. For handling a ton or more of grapes, use a mechanical crusher-stemmer, Examples ofthese devices are shown in figure 2 and are detailed in Chapter 8 in the section on equipment and supplies. Using a small crusher-stemmer, wo persons can crush and stem a ton of grapes in about I hour. Smaller lots of grapes can be crushed, using a hand-operated, roller-type crusher. In either case, (0 collect the crushed grapes (must), the machine is placed and supported above a container, such as a large polyethylene plastic tub or garbage can. only a crusher is used, place chicken wire over the collecting container to separate out most of the stems; these ate intermittently discarded, as necessary. Small, fragmented pieces of stems that get into the must will increase the wine's astringency or bitterness and their Inclusion should be avoided as much as possible. The important objective is to minimize bitterness by thor- oughly crushing the berries without macerating the seeds, and while recovering all of the skins and juice in the must After stemming and crushing, the fermentors Fg Essencil steps in red wine making.Fig 2. Left hand-operatedcoller-cruser: righ, crasher-stemmer, ted for motor drive ate filed with the must to about two-thirds capacity, to avoid foaming-over during fermentation. Probably the most practical and least expensive fermentation vessel isa 32-gallon plastic garbage can (polyethylene plastic is preferable). About eight or nine are needed to handle aton of crushed grapes. Aer all of the must has been poured into the fer- mentors and sulfur dioxide has been added (see below), the fetmentors should be covered with cheesecloth or plastic to keep out insects. Temperature, total soluble solids, titratable acidity, and the free and total SO2 (note analyses section) of the must in each fermentor should bbe determined and the results recorded Adding sulfur dioxide Sulfur dioxide (SO,) is a chemical compound that bas been used in wine making for more than a century. Because it is known that wine yeast produce small amounts of 50; during fermentation, SO; can be con- sidered a natural constituent of wine, The amounts pro- duced vary widely, and to insure against deficiencies, commercial wineries add small amounts to inhibit de- velopment of such spoilage microorganisms as vinegar bacteria and spoilage yeast, and to prevent oxidation and browning, Although SO, has proved an effective wine preservative, its use, as with other food additives, has been brought into question. Despite 75 years of enological research, no satisfactory alternative practice has been found for preventing microbial spoilage and oxidation of wine. In reaction to reports that suggested that a very small number of asthmatics ran a potential risk if they consumed wine containing SO, new federal regulations were adopted in 1986 for using SO>. As of January 9, 1988, whenever a wine contains 10 ppm or ‘more total SO;, the label will be requited to disclose that it “contains sulfites” Judicious and moderate use of SO; has long been recommended. Recent research shows thatthe best qual- ity wines are made when SO, has been used both before and after fermentation. Some commercial winery expe- rience indicates that use of SO2, before alcoholic fer- mentation, can be minimized or even omitted when freshly harvested grapes are free of mold, mildew, rot, or any other defects (cracked or broken skins), and these grapes are handled, throughout the wine making, process, under strict sanitary conditions and in a tem- perature-controlled environment. These practices are more often successful in making red wines than in ma ing whites. Furthermore, SO: should be added after fer- mentation when usual storage or aging is contemplated and most certainly at bottling to prevent oxidation. For most home winemakers. adding SO; is recom- mended. It has been observed that the home winemaker is generally unable to achieve strict sanitation, and hence can benefit from the judicious use of $O;. As stated, adding a small amount inhibits development of molds, wild yeast, and undesirable bacteria, especially vinegar bacteria. For grapes free of mildew, rot, or mold, usually from 50 t0 100 parts per million (ppm) is used or about 75 ppm is adequate, This mild antiseptic is commonly used in the form of potassium metabisulfite (K:S,0s), and is available from home wine making suppliers. To obtain 75 ppm of SO, add Y ounce (slightly less than 1 level teaspoon) to each 10 gallons of juice or must. For grapes that have appreciable amounts of moldiness, rot, or broken berries, use twice this amount of SO,. To add SO,, dissolve the metabisulfite in a small portion of the juice; then add this back to the bulk of the must 10 be treated and mix thoroughly. Allow this mixture tostand about 2 hours before adding the wine yeast starter ccalture (see next step). For the beginner, some precautions about usit and handling SO; are in order. Adding too much S common mistake, can delay onset of fermentation; ex- cessive amounts can actually prevent it, Using too little or no SO; can result in the wine turning to vinegar or spoiling, Therefore, calculate and weigh $O, additions carefully. The K.5:05 will lose its strength after being opened and during subsequent storage and openings, especially if it gets damp. Therefore, purchase only enough for one season's use and store tightly closed ina ‘cool, dry place. As with other chemicals, avoid skin and ‘eye contact, wear protective gloves, and wash hands thoroughly after use. Finally, because wine making at home is a batch ‘operation, itis a relatively slow process. Hence, during ‘crushing and stemming, small portions of juice or must may be obtained over several hours. With this in mind ‘we recommend adding SO; in increments during crush- ing and stemming rather than after this operation has been completed. Thus, as each 10 gallons of juice or rust is obtained, add SO; to insure its thorough distri- bution in the final mixture and to prevent oxidation during crushing As mentioned, accurate measurement of SO; is erit- ical, Because repeated weighings of K:S:O; are tedious and can cause error, use a concentrated SO; stock solu: tion of known strength. A 10 percent solution of K:S,0, (containing about 6 percent available $O:) is readily prepared and convenient. Remember, however: The so- lution loses its strength upon repeated opening and should be replaced with a fresh solution after 1 to 2 weeks. Depending upon amounts of must or wine to be treated, the stock solution volumes involved can be quite small and need to be measured in metric units thats, milliliters (ml) Adding To prepare and se the 10 percent stock solution of i5i0s, ‘he allowing supplies ae needed: Several sizes of graduated cylinders—10, 100, and 1,000 ml (Ler I and 20-mal transfer plpetes (the Loma plpete ‘must be graduated in 0.0L-ml intervals) anda I-liter(L glass reagent boule that cam be tightly stoppered with a wpered rubber or cork stopper. The solution is made by carefully ‘weighing out 100 grame (g) (352 ounces (oz) of poeassiam metabisulite and dissolving in 1L of water, The purity of ‘the K,$i0, shouldbe noted on the label and if tis es than 100 percent, compensate fr this difference by an appropriate adjustment tothe amount weighed. For example, if the la ‘0 the K550s container indicates its purity to be 964 per- eat, then 1037 g (3.5 oz) KSiOy is required for 2.10, percent solution (100 g divided hy 0.964 = 103.7 g). Dis- solve the KiS:0s in I'L of water and place in che reagent Dotte, stopper tightly, label contents, and store in a cool place Table 4 shows the various volumes in ml of the stock solution required for final concentrations of SO, at given volumes of juice or wine. Sulfur dioxide solu- tions volatilize readily and the vapors can seriously irritate eyes, nose, throat, and lungs. Therefore, when dispensing aliquots of the K,S;O; stock solution avoid breathing the fumes, use in a well-ventilated area, and wear a fume-type face mask if you are especialy sensi- tive. It may be helpful to position a fan so that the furnes are blown away from your face or work with the SO solution outdoors. All measurements of small volumes that requite use of pipettes should be done with a rub- ber bulb to supply suction, Never use your mouth! Table 4 Making SO, stock solution ditions ‘Desired feat SO, concentration (pen? Musvwine 10 20 25° 30 40 50 75 100 ea ‘Add mi of 10% stock solution tao oF 1s 6 2 3 oD us 1526 33 30536613 Wn 3366 82 99 13 16 25033 1 6 13 16 20 26 33 49 66 2 1326 33 39 53 66 99 11 3 29 39 49 59 79 99 148 197 + 26 53 66 79 103 131 197 263 5 33 66 82 99 131 164 246 329 0 66 131 164 197 263 329 493 057 ro 164 329 411 493 657 821 1232 1643 30 329 657 821 9RO 1314 1685 2665 3266 “The volumes indicated assume 100 percent purity of the possum smetaisulive (5:05) and fl strength ofthe stock solutionAdding pure wine yeast starter cultures The use of pure wine yeast starter cultures to pro- mote alcoholic fermentation is practiced widely in com- mercial wine making and is recommended for the home ‘winemaker. The active dry form of wine yeast is avail- able from home wine shops. Of two strains commonly used, Montrachet and Champagne, avoid Montrachet if the grapes were sulfured a few weeks before harvest, as this strain readily produces hydrogen sulfide when re. sidual sulfur is present. Usually, ewo 5-gram packets of dry yeast pellets, sprinkled on the must surface with mixing, provide an adequate inoculum for each 10 gal- lons of must. If the must is highly sulfited, or it is difficul to start fermentation, use twice this amount of yeast. For best results, the yeast should be rehydrated before use. If rehydration is not followed precisely, yeast activity will be reduced. Therefore, we do not recom- mend it for very small lots. sees ses veveeeeEeLEE ‘To rchydrate, add 1 Hilogram of dry yeast pelts to about 2 sallons of water or must previously warmed to 100" 105°F (08° (041°C). Afer 10 0 20 minutes mix wel and use 25.6 ‘eof this mixtare to inoculate ech 100 gal of must. This spproximacely equivalent to an inoculation rte of Ig yeast, pet gal of must. Note that higher temperatures, lower temper ‘ures, and prolonged scaking in wate, even at the correct temperature, can all reduce yeas activity, Some winemakers prefer to acclimatize the yeast by first growing it in juice or sweetened diluted wine until about one-half ofthe sugar has fermented. This actively fermenting mixture of yeast cells is then used as the inoculum. Alcoholic fermentation Grape wine is the alcoholic product of the fermen- tation of grape juice, and the essential feature of this fermentation is the conversion of the grape sugars, glu- cose and fructose, to ethyl alcohol (ethanol), carbon dioxide (released as a gas), and flavor components. This complex process is accomplished by living yeast cells and is illustrated in the following chemical equation: Call:0 yest CHSCROH 1 mols ghacose 2 molecules ethanol 1806 9g cor + Lmolecules carbon dione gas 88 The alcohol produced through fermentation is a ‘wine's major flavor component. It also affects the solu- bility of many wine constituents, Some is used in form- ing other flavor compounds. It also enhances wine's 10 resistance to spoilage. Moreover, wines traditionally are classified according to their alcoholic content. Indeed, the amount of alcohol formed from a given amount of grape sugar is of considerable practical importance to the winemaker. According to the equation above, the ‘maximum theoretical yield of ethanol is 51.1 percent of the molecular weight of the sugar (92/180 * 100 = 51.1), However, in actual practice, the alcohol yield is somewhat lower, since some sugar is utilized by the yeast for growth and for production of small amounts of other compounds. Also fermentation efficiency (abil ity to produce alcohol) of the yeast is not perfect or constant, and in addition some alcohol escapes with the evolution of the carbon dioxide gas. Hence, on the average, actual alcohol yields are about 47 percent by weight, instead of the 51.1 percent just shown in the previous calculation, Givetia known amount of sugar in grapes, it should be possible to estimate the amount of alcohol that can result from fermentation. Thus, a must containing 22 percent sugar by weight should yield a wine containing 10.34 percent alcohol by weight (22 x 0.47 = 10.34), Note, however, that the alcoholic content of wine is expressed as percent by volume, owing to the method of its measurement. From specific gravity tables, the 10.34 percent value converts to 12.82 percent alcohol by volume, Unfortunately, this relatively simple method cannot be used to calculate how much alcohol can be obtained from a must of a certain sugar content, 2s determined by the *Brix measurement. This latter term, described ‘more fully later on, denotes the percent sugar of pure solutions. Since must or grape juice contains nonsugar- dissolved solids, the °Brix value must be corrected to sive a more true percentage of the sugar content, when alcohol production is estimated. The amount of non- sugar solids has been estimated to average 3.0 percent Thus, °Brix minus 3.0 gives the must’s approximace sugar content. This value, multiplied by its specific ‘gravity (table 5) and then multiplied by the fermenta- ton conversion factor of 0.59 (this term represents the alcohol by volume that forms from 1 gram of sugar), will provide an estimate of the approximate percent alcohol by volume resulting from a given °Brix must. The following example illustrates this convenient calculation: Assume that a given must or juice is 22.5¢ Brix. Subtracting the nonsugar correction factor of 3.0 percent, the “true” sugar content is actually 19.5 percent by weight. To convert this to percent by volume, multi- ply 19.5 by the specific gravity of 1.0803 (obtained from table 5). Then multiply by 0.59. The result is an approx: imate alcoholic content of 12.4 percent by volume. Usually, in natural grape table wine fermentations (where no sugar is added) the alcohol produced ranges between 11 and 14 percent by volume, depending upon