Clarification of Wine L. G. SAYWELL, University of California, Berkeley, Calif.
T
HE clouding of wine is a problem important to the wine industries of Europe, Australia, and the United States. In general, the causative factors may be similar, b u t the composition of the wines from the different production areas m.ay vary considerably and thus change the nature of occurrence of clouding. In relation to California wines, many European wines are high in tannin and acidity, while certain Australian wines are markedly low in tannin. As a result, wine types that may be stable in France may develop a cloud in California or Australia. Further, newer wines are often cloudy and some type of clarification then becomes a routine part of the manufacturing process. Because many of the methods of clarification formerly used for California wines are now being found inadequate, it has become necessary to study the general process of wine clarification with the object of securing a permanently brilliant product. Previous California practice (2) utilized gelatin, egg white, isinglass, and tannin as the chief clarification or fining agents. Inadequate or improper use of these materials generally results in a reclouding of the clarified product, arid often tank quantities of wine from juice of the same pressing and same later treatment will vary in their stability to clouding. Many factors may be responsible for this occurrence. The iron content of such clouded wines is often higher than that of the unclouded wines, and consequently, the presence of the larger amount of iron has been held to cause the clouding. This may be confirmed b y adding iron t o a clear sample and thereby inducing clouding, a control remaining clear. For clearing with gelatin a high grade of product is used, about one part of gelatin being added to 9000 or 10,000 parts of wine. (Rapid approximation of quantities may be secured by taking the weight of one gallon of wine t o be 8.3 pounds, 130 ounces, or 3.7 kg.) The gelatin is dissolved in warm water, mixed with a few gallons of the wine t o be treated, and added with thorough stirring to the larger volume being clarified. For clearing with egg white, the material (free of yolk) is mixed with warm water and then beaten t o a fluffy foam. One quart of water may be used for the whites from 4 eggs, and the whites frbm 4 t o 8 eggs are required for each 100 gallons of wine. This original aqueous solution of egg white should be diluted with about 10 volumes of wine before adding to the tank quantity. Mixing should be thorough. The amount of isinglass required may vary considerably, one part of isinglass in 7000 t o 25,000 parts of nine being used. The optimum concentration should be determined on smaller quantities of wine at the time of application. The estimated quantity of isinglass is placed in a small volume of cold water for several hours, or until much of the swelling has occurred. The mixture is thoroughly stirred,, heated nearly to boiling, passed through a sieve (or heavy cloth), and cooled. Small quantities of wine are then added, with constant stirring, until a light fluid consistency is obtained. This solution may be 1 to 2 gallons in volume. Tannin, used with gelatin for clarifying white wine, may be added one t o tu70 days before the gelatin. One part of tannin is added to 5000 or 10,000 parts of wine. A ure tannin is recommended in order to avoid the introduction ofimpurities that may tend t o produce later reclouding. Several tannins analyzed by the official method ( I ) showed on the basis of a pure tannic acid (Eastman Kodak Company), the following quantities of tannin : U. S. P. grade, 90 per cent; oak tannin, 94 per cent; California grape tannin, 75 per cent; and Australian gra e seed tannin, 65 per cent. Tests in this laboratory (unpublisgid data) do not indicate complete verification of the broad claims made for the Australian product.
The use of a filter aid in the filtration is common. From less than 0.1 per cent to 5 per cent is added, depending upon the condition of the wine and the type of filter used. Its
use increases the rate of flow and the brilliancy of the filtrate, but results with different wines vary widely. In general, 0.1 or 0.2 per cent of filter aid has been found most satisfactory. An important criticism of the use of filter aids has been that the iron content of the wine was increased thereby, This condition apparently depends upon the filter aid used. A certain diatomaceous earth of grayish color had been used in a plant with very unsatisfactory results, added iron being suspected as a possible factor. Analysis of the untreated wine indicated an iron content of 17.3 parts per million, while the treated wine contained 51.5 p. p. m. Evidently, where the only difference in treatment had been the use of the earth, the earth had increased the iron content. With a better quality of diatomaceous earth, repeated experiments indicate a relatively small or even negligible increase of iron content. Two sam les were filtered, using 5 per cent of a 50-50 mixture of Super-$el and Hi-Flo. The original untreated samples contained 14.3 and 17.5 p. p. m. of iron, while the samples treated with filter aid contained 12.8 and 16.4 p. p. m. of iron, respectively. Portions of another wine containing originally 18.7 p. p. m. of iron were treated with 0.1 per cent SuperCel and with 0.1 per cent of a 50-50 mixture of Super-Cel and HiFlo. These portions were found to contain a final iron content of 18.2 and 17.6 p. p. m. of iron, respective1 All iron analyses reported in this paper are by the method of gtugart (9). Treatment with gelatin, egg white, isinglass, or tannin, with or without a diatomaceous earth filter aid, may result in only a temporary clarification followed by reclouding, and occasionally may not even effect an initial clarification. This situation is comparable to that occurring with wine vinegar, where experiments covering three years' time (8) have shown that a consideration of the colloidal properties of the liquid considerably aided in adapting methods for clearing. On this basis the use of the natural hydrous silicate of alumina, bentonite, was tried and found very satisfactory in comparison to other methods.
.
USE OF BENTONITE It is desirable to remove any excess of iron a t the time of clarification. The earlier methods of clarification and iron removal involved the use of gelatin and tannin with aeration (4),an oxygen treatment alone ( 5 ) , or the use of potassium ferrocyanide to precipitate the iron (6). A general discussion of the relation of iron to clouding or c a s e is given by Ribereau-Gayon and Peynaud (7) for French wines. None of these methods involved the use of bentonite, but the results with vinegar suggested the desirability of testing its use with wine. Preliminary tests indicated that clarification by bentonite was satisfactory, as judged by repeated chilling and heating tests for exposure to sunlight and by standing a t 30" C. Qualitative tests for iron indicated a reduction in content. The normal iron content of California wine varies rather widely with wines and their age, but generally averages about 10 p. p. m. Analyses of representative two- and three-yearold wines that have remained brilliantly clear show 15.7, 15.6, 6.7, 11.9, 9 1, 11.5, and 3.0 p. p. m. of iron. In general, the role of iron in causing cloudiness is dependent upon its state of oxidation (3,7 ) , the ferric iron being associated with the clouding. The oxidation of ferrous iron to ferric iron may be relatively slow, but if the total iron content is low, clouding from this cause is largely prevented. Several series of tests with bentonite have been completed on different wines with varying iron contents. A wine with an original iron content of 16.7 p. p. m. was treated with 1 part
981
INDUSTRIAL AND ENGINEERING
982
of bentonite to 2000 parts of wine, and with the same quantlty of bentonite to which a peptizing agent had been added. The cleared samples contained 7.4 and 7.2 p. p. m. of iron. With a similar sample containing 17.5 p. p. m. of iron, treatment with bentonite at 1 to 2000 reduced the iron content to 6.3 p. p. m., while treatment with casein at 1 to 2000 for purposes of comparison resulted in an iron content of 13.1 p. p. m. The protein content of the original sample was 0.19 per cent, while the clarified portions contained 0.18 per cent each. A 2 per cent solution Qf casein in a 1.5 per cent aqueous solution of potassium carbonate was used for adding the casein t o the wine. Thorough mix-
ing is essential.
A report that material sold as bentonite left an earthy flavor was investigated, as this had not been observed in tests with the Clay Spur, Wyo., bentonite used exclusively. It was found that the material represented as bentonite was probably fuller's earth. Treatment of another lot of the same wine with Clay Spur bentonite did not impart an earthy taste. A survey of the bentonites available on the California ma,rket resulted in the collection of samples from several sources. The bentonite was prepared for use by making a 5 per cent suspension of the material. An estimated quantity of water {or previously clarified wine) was placed in an appropriate container equipped with a stirring device, and the bentonite powder was gradually sifted in with vigorous stirring. Agitation was continued for several minutes, after which small clumps of bentonite were worked into suspension by hand. This method of preparation has been found the most satisfactory if the addition of the powder is not too rapid. Appropriate volumes of this suspension were added to the wine to give 1 part of bentonite to 2000 parts of wine. After treatment the filtrates were tasted for alteration of flavor by four persons not familiar with the samples or their treatment. No off flavors were noted. These portions were also analyzed for their iron, total acid, and protein content. It appeared that the decrease in protein (1) content (X X 6.25) also might be related to the general clearing ability of the bentonite. TABLE I.
EFFEZT O F VlRIOL?S BENTONITES ON W I N E
COMPOSITION (1 part of bentonite in 2000 parts of wine)
SAMPLE
BENTONITE USED
TOTAL PROTEIN IRON ACID G./100
Control A None Clay Spur, Wyo. A1 A2 Volclay, Wyo. A3 Western talc A4,Calif. A4 Baroid 9, Calif. A5 Baroid B Calif. Baroid A15, Calif. A6 Clay Spur A7 peptonizing agent
+
cc. P. 3 . m. 0.21 6.7 0.19 6.2 0.19 6.6 0.19 6.8 0.20 6.8 8.4 0.20 6.8 0.20 6.2 0.19
G./100 cc.
0.63 0.53 0.53 0.53 0.53 0.50 0.51 0.50
The data presented in Table I indicate a slight decrease in protein content, a marked decrease in iron content with one sample, and a slight (if significant) decrease with another. With the last three bentonites there was also a reduction in total acidity of the wine, which would be of value with wines of high acidity, Clay Spur bentonite would appear the most desirable of the various samples tested. The wine used for the test had an originally low iron content, the experiment being designed to test primarily the effect on flavor and protein- removal, In a subsequent experiment wines of higher iron content were used, adding bentonites used in samples A l l A2, A6, and A7 to the wine a t 1 to 2000. A clarification with casein is given for comparison. The filtrates were analyzed for protein and iron content. The data given in Table I1 indicate a considerable removal of iron, the Wyoming bentonites probably being more efficient in this respect. About 50 per cent of the iron in the original wine is removed by these clays. Several phases of this investigation are being continued.
CHEMISTRY
Vol. 26, No. 9
TABLE 11. REMOVAL OF IRON FROM WINE BY BENTOXITE SAXPLE Control B B1 B2 B3 B4 B5 Control C C1 c2
AND CASEIN (1 part of bentonite i n 2000 parts of wine) PR oT EIN BENTONITE USED G./lOO cc. 0.18 Clay Spur, Wyo. 0.17 Volclay, Wyo. 0.17 Baroid A-5, Calif. 0.16 Clay Spur peptonizing agent 0.16 Casein (1 to 2000) 0.16 0.25 None Clay Spur Wyo. 0.24 Clay Spur' peptonizing agent 0.23
+
+
IRON G./100 c c .
28.5 15.5 16.1 19.3 19.7 18.2 25.7 11.4 11.4
In general, the appropriate use of bentonite, particularly that from Wyoming, results in a brilliantly clear wine which is stable to higher and lower changes in temperature, to sunlight, and to storage a t average room temperature. There is a rapid rate of flocculation and settling after addition of the bentonite to the wine, and the supernatant liquid may be very rapidly filtered a short time thereafter. This results in a considerable saving of time in comparison to clarification by gelatin or isinglass, for which 10 to 14 days or more may be required for sedimentation. The bentonite method has resulted in positive clarification rather than uncertainty and frequent nonclarification with other agents. The use of added tannin is not necessary in order to maintain the original wine color, since bentonite does not decolorize or appreciably reduce the color. This is of considerable importance in the treatment of delicately colored wine. In all cases observed the facility of Clarification and brilliance obtained is enhanced by adding the bentonite to wine heated to a temperature of 120" to 180" F. (82" C.) (8). Heating and cooling should be continuous and in a closed system. Plant practice has suggested the use of a filter aid with the bentonite, the resulting precipitate being firmer. Accordingly, 0.1 per cent of Super-Cel and 0.1 per cent of a mixture of equal parts of Super-Cel and Hi-Flo were added with Clay Spur bentonite (1 to 2000) to a portion of the wine, control B in Table 11. After flocculation and filt'ration the original iron content of 28.5 p. p. m. was reduced to 19.1 and 18.5 p. p. m., respectively. The filtering velocity and firmness of cake were increased. For a final polishing filtration just before bottling the wine, Seita E. K. type asbestos filters and Berkefeld candle filters have been found very satisfactory. Small plate and frame and also pulp filters have been used, adding a mixture of 10 parts of filter aid and 1 part of asbestos to the wine to Ee filtered. The individual conditions of filtration and the resulting velocities vary with the wine being treated. In general small quantities of filter aid are required with the plate and frame filter.
ACKNOWLEDGMENT The writer takes pleasure in acknowledging the assistance of B. B. Cunningham in making the iron determinations.
LITERATURE CITED (1) ;issoc. Official Agr. Chem:, M e t h o d s of Analysis (1930). ( 3 ) Bioletti, F. T.,Univ. Calif. E x p t . S t a . , Bull. 213, 438 (1911). (Out of p r i n t . ) (3) Brown, J. G . , Fruit Products J.,11, 274 (1932). (4) Castella, F. de, Dept. Agr. Victoria, Australia, Bull. 48, 2 3 (1925). (5) G r a n c h a m p , L. E., Chimie & Industrie, Special No. 5 6 1 (1925). (6) Heide, C. van der, Geisenheim Wine C h e m . E x p t . S t a . Bull. (1923) ; Mitt.deut. Landw. ges., 37, 687 (1922). (7) Ribereau-Gayon, J., a n d P e y n a u d , E., Rev. vit., 76, 309, 341, 379 (1932). (8) Saywell, L. G., IXD. EXQ.CHEM.,26, 379 (1934). (9) Stugart, R., Ibid., Anal. Ed., 3,390 (1931). RECEIVEDApril 12, 1934. Presented before the Division of Agricultural and Food Chemistry a t the S7th Meeting of the .\merican Chemical Society. S t . Petersburg, Fla., March 25 t o 30, 1934.
