Effect of Filter Aids and Filter Materials on Wine Composition L. G. S-IYWELL
Data presented indicate that there may be a limited increase in the iron and calcium content of the wine as a result of filtration. This increase appears to vary with the wine being filtered and the conditions of filtration. In general, large quantities of wine may be filtered satisfactorily with the best grades of filter aids; with some of the cellulose and asbestos pads of known composition which are available. the iron and calcium increase was negligible. No increases in iron or calcium content were observed with porous silica candle filtration. The advantages of diatomaceous silica filter aid and porous silica candle filters w i t h respect to economy, sanitation, and effectiveness of filtration are indicated. It has been demonstrated that certain wines, which become cloudy even though there is no measurable increase in iron or calcium content and no precipitation of colloidal materials, become cloud> and form a deposit of sediment as a result of the presence and growth of certain microorganisms in the wine. I t was found that with many wines the usual diatomaceous silica filter aid filtration produced a filtrate free of such microorganisms. Such wines then remained permanently brilliant for long storage periods.
University of California, Berkeley, Calif.
certain types of filtering materials were employed, that the Tvine which had been filtered, frequently would become cloudy, whereas the unfiltered portion would remain brilliantly clear. In some instances even sediment formation was observed in the filtered portions. Therefore, a study was made of several types of filters employing various filtering materials and their effect on the composition of wine.
Filtering Equipment and Procedure Filters using cellulose or paper pulp, generally as wet compressed pads or cylinders, were used. Filters employing a porous silica candle were also utilized. Filtration of wine through relatively thin compressed pads of cellulose or cotton fiber, with or without added asbestos fiber, was studied. I n addition, a study was made of chamber types of filters employing either cotton cloth or wire-screen filtering medium supports with the use of either fibered asbestos or diatomaceous silica as precoats, and diatomaceous silica as a filter aid. Standard commercial products were used in all tests. Filtration with such equipment and filtering media made it possible to secure all qualities ranging from rough to, and including, brilliant polishing filtration. In general, the actual filtration tests were made in the wineries, observations being made on tank quantities of wine varying from 500 to 35,000 gallons each. Laboratory tests on smaller volumes will be so indicated. Practically all types of both sweet and dry wines were employed. Preliminary microscopic and chemical examination indicated that, xhen clouding or sedimentation occurred after filtering a wine, such action was frequently associated Kith either a growth and accumulation of microorganisms, or with increased iron and/or calcium concentrations. In some instances all these factors were consequential. As a result, all filtered wines were examined for the relative removal or increase of numbers and kind of microorganisms and of iron and calcium. Microscopic observations were made using wine, naturally accumulated sediments, and sediments from centrifuging small portions of a cloudy wine. A magnification of 600 diameters, dry, was usually YEW L.4RGE-CHAMBER
D
URING a study of the stability of brilliantly clarified vines. it was observed that some such wines became hazy or cloudy subsequent to certain filtrations. These observations were made in both the laboratory and in the wineries during 1933 and 1934 vintage years. In the wineries these changes in the appearance of the wines were a considerable annoyance to the wine maker. The relation of such cases of clouding to the filtration process was established by the general procedure of clarifying a large volume of wine with gelatin, isinglass, casein, and/or bentonite ( d ) , and then dividing it into two lesser and about equal volumes, one volume being filtered and the other merely pumped over into a smaller container. On continued observation of these smaller volumes of wine, it was found, when 1215
TYPEOF
LOW4X FIL'rER
1246
IICDUSTRIAL AND ENGINEERIICG CHEMISTRY
employed, though magnification of 1350 diameters, with an oil immersion objective, was used frequently. Many samples were incubated at 30" C. before observation. Iron and calcium determinations were made by modified methods detailed in another communication ( 3 ) . In brief, all samples were wet ashed, using 60 per cent perchloric acid with either or both concentrated sulfuric and nitric acids. After complete digestion and appropriate dilution, the iron content was determined by means of the colorimetric method using a thioglycolic acid reagent. Calcium was determined by a modified oxalate-permanganate method. Appropriate controls and blank determinations confirmed the accuracy of the methods.
Cellulose Pulp Filtration Filters employing cellulose or paper pulp have been used quite generally in the wine industry. When a wine is relatively clear before filtration, relatively large volumes may be filtered in one cycle. However, when an attempt is made to filter a cloudy wine, the cycle frequently becomes much shorter because the solids removed from the wine form a slimy deposit on the surface of the pulp, through which the rate of flow is greatly reduced. It also happens that brilliant filtration of cloudy wines is not secured, apparently, because of direct channeling of the pulp filter cake. In general, it was observed that other types of filters gave a more satisfactory polish to the wine when large quantities were filtered. Examination of wines before and after filtration through a cellulose pulp filter did not indicate any appreciable increase in iron and calcium content, and the wines exhibited continued stability with respect to clouding and sedimentation related to these factors. On the contrary, it was frequently observed that if portions of the unfiltered and the corresponding filtered wines were incubated for 2 weeks t o 3 months, the filtered wines would contain considerably greater amounts of microorganisms such as acetic acid, lactic acid and town6 bacteria, and wine yeasts. In such instances the unfiltered samples would remain clear or slightly hazy with slight sediment formation, whereas the filtered samples would become hazy or even cloudy and a very heavy sediment would be formed. A study was made of several filter pulps taken from the filters, from the pulp washers during the washing operation, and just after washing was finished. Microscopic examination showed that the mechanical washing had not removed the microorganisms from the matrix of the cellulose fibers in the small clumps of pulp. Further, if a small portion of such pulp was added to the clarified wine and the sample incubated for 2 to 4 weeks, clouding and sedimentation would develop. Parallel controls without added pulp would remain clear. Much of this trouble could be avoided by using small concentrations of potassium metabisulfite or similar agent, or steam, to sterilize the pulp. However, considerable care was necessary with the use of such methods of sterilization in order to avoid hydrolysis of the pulp and the resulting great decrease of its value as a filtering medium.
Porous Candle Filtration Analyses of wines before and after filtration through filters with porous silica candles showed no appreciable increase in iron and calcium content. Incubation of such wines demonstrated that complete removal of the microorganisms common to wine had been secured when candles of fine porosity were used. With cloudy wines, the removed wine solids quickly formed a slimy coating over the candle, greatly reducing the rate of flow of filtered liquid, With wines that previously had been clarified and were free of appreciable suspended colloidal material, these filters which are of very fine porosity were particularly suitable for securing a brilliant polishing filtration with a satisfactory rate of flow. Wines which remained brilliantly clear without any filtration also remained brilliantly
VOL. 27, NO. 11
clear after filtration through standard porous silica candles of fine porosity.
Iron Pick-up from Cellulose Pad-Asbestos Filtration The effect on the mine of filtering it through thin, tightly compressed pads of cellulose or cotton fiber, with or without added asbestos fiber, was studied. In general, the effect varied widely depending upon the composition of the pad. Such variation occurred not only between pads of different make but also between pads of the same kind of one given make. The principal changes in the wine were increases of iron and calcium content and decreases in numbers of microorganisms present. In early tests it was noted occasionally that an actual decrease in the iron content occurred when certain wines were filtered, but that with other wines there would be an increase, even though the same kind of pads from the same production lot were used in all instances. As an example, a white wine containing 12 parts per million (p. p. m.) of iron was filtered through a tight pad filter, and the resulting filtrate contained between 9 and 10 p. p. m. of iron. In the same cellar a similar kind of wine contained 8 p. p. m. of iron before filtering and between 9 and 10 p. p. m. after filtering. Portions of the same unfiltered wines were then filtered through a porous silica candle filter with the result that after filtration the first wine contained 9 p. p. m. of iron and the second contained between 7 and 8 p. p. m. That is, filtering the first wine through the candle filter also produced a decrease in iron content, but with the second wine no increase similar to that with the pad filter was observed. This and similar results were found to be explained by the observation that the first wine was very hazy before filtration and that, with the removal of the suspended solids by filtration, some of the iron apparently was thereby removed. The second wine was already very clear and, as evidenced by the small accumulation of solids on the pad, very little suspended material (with which the iron might be associated) was removed. A confirmation of the validity of this explanation was obtained in the following manner: -4 5-gallon volume of the first of the above wines was filtered through a small filter with one candle, and after filtration the entire residue was carefully washed from the candle, ashed, and analyzed for iron. A total of 0.043 gram of iron was found in the residue, Calculated back to the basis of the 5 gallons of wine, this would correspond t o 2.2 p. p. m. of iron removed. This recovery equaled very closely the losses previously noted, considering the accuracy of the methods for determining small amounts of iron. As a result, measurements of the increase or decrease of iron and calcium were made only with very clear wines or on a standard tartaric acid solution. A concentration of one per cent tartaric acid was taken as representing the maximum conditions of acidity occurring in a wine. It was soon ascertained which pads imparted iron to the wine, and quantities of approximately 500 gallons of each of several clear wines were filtered with these pads. The wines may be designated by the tank numbers and the data are as follow: Before filtration the iron content of tank 125 was 10 p. p. m., after filtration it was 12 p. p. m.; likewise, with tank 187 before filtration there were 5 p. p. m. iron, and 6.5 p. p. m. after; tank 119 contained 10 p. p, m. of iron, and, after filtration into two smaller casks, the iron contents were 11 and 12 p. p. m., respectively. Another wine in tank 136 contained 4 p. p. m. before and 6 p. p. m. after filtration. Since it was not practical to employ several different makes of pads for the filtration of each of several wines in a winery, a standard laboratory test was developed so that the difterent pads could be evaluated on a relative basis. Using the wines
diccussed in the previous parngraph, it was iound that cimilar r e s u l t s could be obtained kJV digesting 4 to 5 grams of the finely divided pad material 111 200 cc. of one per cent tartaric acid solution at about SO’C. for 30 minutes. The iron thus r e m 0 ved corresponded quite closely with the iron reiiioved by the action of nine filtering through the pad for a period of 1 to 5 hours A similar clige-tion using concentrated hydrochloric acid was made and assumed to give the total iron present.. for,. after comDletelv &ashing several pad residues ‘THIU-CH IVBER and redigesting with acid, no increaseziron removal was. observed. Similar tests were made on asbestos fiber for filtering. The resulting data are presented in Table I. There is a wide variation in the apparent total iron content of the cellulose, celluloseand asbestos pads, and in the various lots of asbestos. There is a wide variation in the amounts of iron soluble in one per cent tartaric acid solution, and it appears important to observe that the percentage or’ the total iron content which is soluble in one per cent tartaric acid also varies widely. Under the conditions of these studies, the total iron content’ is no criterion of the tartaric-acid-soluble iron. In like manner, this was demonst,rated to be the case with wine in winery filtrations. For the winery tests 500gallon quantities of the wine previously designated as tank 125 (a sauterne) were filtered, using pads corresponding to samples numbered 4, 111, 12, and 14 in Table I. The wine had an original iron content of 10 p. p. m., whereas, after filtering through these pads, the iron contents were l o + , 1 2 + , 11, and l l f p. p. m., respectively. It is evident that, though samples 11 and 12 (Table I) are not relatively high in iron content, the iron is practically all wine-soluble and results in a greater or equal iron contamination than occurs with the use of pads like samples 14, which are of much greater total iron content. This however, does not minimize the danger of the original high-iron content of pads with which the iron may be largely wine-soluble under other conditions. For these tests fifty pads of each kind were used in a filter. The pads were 12 or 13 inches in diameter. On t,he basis of TABLEI. PERCEXTAGE IRONCONTEXTOF CELLULOSE AND CELLULOSE-.k3BESTOS F I L T E R PADS AND O F ASBE~TOSFIBER PULPFOR FILTERING Sample
bpprox. .\sbestoP Content,
1
3I1
? 3
40 50
5
10 100 c
66
100
8 9
l0OC
10
100
11 12
30 30 90 30 15 30
4
7
136 146 156 166 17 b
I8b 19
10
100
;
100 6 100 c 20 l0OC
F e Content by HCI
0,044 0.043 0.032 0.033 0.630 0.890 0 I022 0.434 0,442 0.390 0,099 0.050 0,260 0,300 0,730 0.369 0.732 0,820 0.284
Fe Content b y Tartaric Acid
Soluhle Fe”
0.0186
41.;
0,0229 0.0328 0.0247 0.0490 0.0614 0.0123 0.0364 0.0625
53.4 63 0 75 5 78.6 69 0 57 4
0.0630
8.4
14.1 16 1
0.0986 0.0491
98.8
0.0870
33.4 31.1 9 5 20.3 25.5 15.2 19.3 83.8
0,0935 0 0692 O.Oi50
0.1870 0.1248
98.4
0.0550 20 0.220 0.1846 Per cent of HC1-soluble iron also soluble in one per cent tnrtaric acid. Imported product. Asbestos fiber; therefore assumed to be 100 per cent on basis of high ash eontent. a
Lo\iix FILTER USEDI\ B IRREI.-FII,LING Roo\%
the one per cent tartaric-acid-soluble iron content as given in Table I, and on the dry weight basis of the fifty pads, calculation shows that pads like samples 4, 11, 12, and 14 should give to 500 gallons of wine an increased iron content of 0.6, 2.5, 1.5, and 1.7 p. p, ni., respectively. Since these values are only somewhat higher than those actually approximated in the winery tests, it would appear that much of the wine-soluble iron is removed during the early part of the filtration cycle. This would explain the subsequent clouding sometimes observed xith the wine first filtered when it is placed in separate smaller containers such as casks, barrels, bottling tanks, or bottles. Of the four filtered vines, that with t’he iron content increased to 12f p. p. ni. was observed to become decidedly hazy and that with 11+ p. p. m. became hazy. This haze m s apparent by t’he sixth day after filtration and was of a bluish nature, similar to the typical ferric casje. Similar increases of iron content have been observed on filtration of small volumes of Chablis, Riesling, and muscatel wines with these same types of pads. With a chamber type of filter, using asbestos fiber as the filtering medium, two filtrations of a sauterne type wine with an original iron content of 8 p. p, in. were made. In the filter 4 pounds of the asbestos fiber corresponding to samples 17 and 20 (Table I) vere used in coating approximately 145 square feet of filtering area. The first 500 gallons of filtrate from each filtration were sampled and on analysis showed an iron content of 9+ p. p, m. each. On t’he basis of the one per cent tartaric-acid-soluble iron content of these asbestos fibers as given in Table I, if the entire amount of iron had been removed by the first 500 gallons of wine filtered, there would have been increases in the iron contents of 1.9 and 1.8 p. p. in., respectively. During subsequent storage of these wines, ferric c a s e was not observed, indicating that what may be termed the “iron tolerance” of this wine had not been exceeded. Parallel tests were made as above using sauterne (tank 125) with pads similar to saniples 11 and 14 (Table I) but filtering through about 7000 gallons in each test. Examination of each of these large volumes indicated no appreciable increases in the iron content of the wine above its original 10 p. p. m. Evidently the wine-soluble iron was not markedly greater than when only 500 gallons had been filtered; and as would be expected, the fourteen times greater dilution resulted in only a small increase in iron concentration. Similar results were observed with other filtrations using the asbestos fiber pulp of sample 17 (Table I). The practical significance of these observations is that, when using a large filtering capacity with 8, large number of t,he above pads or a large weight of such asbestos fiber pulp,
1247
INDUSTRIAL AND ENGINEERING CHEMISTRY
1248
VOL. 27. NO. 11
15 (Table 11) using a Chablis wine of original calcium content of 37 p. p. m. After filtration the analyses of the first 500 gallons of wine of each filtration showed calcium contents of 60, 66, 64, 65, 63, and 67 p. p. m., respectively. Laboratory samples of all of these wines developed white sediments on standing a t room temperature for 90 days. At this time the supernatant liquid was filtered off and again analyzed for calcium. For the sauterne samples the calcium contents were then 69, 67, and 73 p. p. m.; the Chablis samples then contained 56, 58, 57, 58, 57, and 56 p. p. ni. calcium. In these samples a decrease of 10 to 15 per cent of the calcium content had occurred. In the winery the initial 500-gallon lots were Calcium Pick-up from Cellulose Pad-Asbestos added t o the corresponding 10,000- or 10,500-gallonquantities Filtration and allowed to become completely mixed. Analysis of samples of these large volumes indicate calcium contents of 21 to At the same time that the data were secured for iron pick-up 23 p. p. m. for the sauterne and 37 to 41 p. p. in. for the Chablis. from cellulose and cellulose-asbestos pads, and from asbestos These data would indicate that much of the wine-soluble fiber pulp filtrations, parallel observations with respect to calcium was removed during the first portion of the filtration calcium were made. The data are recorded in Table 11. period, and that a filtration of a correspondingly large volume Not only do the total and acid-soluble calcium contents vary of wine and the subsequent mixing would result in a reduction widely, but there also is a considerable variation in the proof such calcium content to a concentration only slightly portion of total calcium that is also soluble in the tartaric acid. greater than that of the original wine. Samples from these large volumes have remained clear for over 10 months. The TABLP.11. PERCEXTAGE CALCIUM CONTENT OF CELLULOSE same precautions, therefore, should be observed as were outAKD CELLULOSE-ASBESTOS FILTER PADSAND OF ASBESTOSFIBER lined above with respect to iron. PCLPFOR FILTERISG Similar filtrations of wine were made with asbestos fiber pulps A prox Ca Content like samples 5 and 6 (Table 11). Parallel results were obtained, Ae\estos Ca Content by Tartaric Soluble Sample" Content by HC1 Acid Cab except that with asbestos sample 5, a particular 5000-gallon 0.370 0.103 27.8 1 30 tank of sauterne wine became cloudy and deposited consider0.466 0.142 30.5 2 40 able sediment after 60 days. With the entire 5000 gallons of 0.540 0.19s 26.7 3 50 0.312 0.106 33.8 4 10 this wine there had been an increase of 32 p. p. m. of calcium. 5.58 2.32 41 6 5c lOOd I t appeared probable that the increased calcium was positively 25.30 9.05 36.0 60 lOOd associated with the sedimentation, although other factors 0.368 0.101 27.4 7 10 30.5 15.85 4.87 8 lOOd may have been involved. With wines filtered through pads 5.09 2.39 47.0 9 lOOd 10 lOOd 5.05 2.23 44.2 and asbestos pulps, like samples 1, 2, 3, 4, 5, and 7, no sedimentation was observed. Where large volumes were filtered, 4.69 2.39 51 0 30 11 1.88 0.499 26.9 12 30 pads and asbestos like samples 9, 10, 12, 13, and 14 have been 2.26 0.624 27.6 0.620 26.3 used satisfactorily. it is more desirable to filter through a large volume of wine into one large tank than t o fill small containers directly from the filter. Where small volumes of wine are to be filtered, it appears necessary to use a small-capacity filter even if a longer filtering time is required. These precautions may be largely avoided if the actual wine-soluble iron of such materials is very low and accurately known by the wine maker himself. This is demonstrated by the use of pads and asbestos fiber pulps, such as samples 1, 2, 3, 4, 7, 8, and possibly 5 and 12, of Table I, with which, in winery use, iron pick-up has not been observed.
16 C 17 c 180 19 20 2lC
30 lOOd lOOd
20 lOOd
15
2.52 21.10 22.70 6.95 7.68 2.07
2.10
27.3
0.632 5.39 5.47 2.56 2.89 0,599
25,l 25.6 24.1 36.8 37.6 28.9
Sample designation same as in Table I . Per cent of HC1-soluble calcium also soluble in one per cent tartaric acid. Imported product. d Asbestos fiber: therefore assumed to be 100 per cent on basis of high ash content. a
b
6
On the basis of the one per cent tartaric-acid-soluble calcium content as given in Table 11, and on the dry weight of fifty pads, calculation shows that pads like samples 11 and 15 could give to 500 gallons of wine an increased calcium content of 62 and 38 p. p. m., respectively. This would correspond to 400 and 250 p. p. m. of CaC4H1O6,4H20, respectively. In a similar manner, when using asbestos fiber pulps such as samples 5 and 6, a t the rate of 4 pounds for 145 square feet of filtering surface, the calcium content of 500 gallons of filtered wine could be increased by 150 and 60 p. p. m., respectively. If under the conditions of commercial filtration smaller volumes of wine were put in individual containers and an equal or greater amount of calcium were wine-soluble, somewhat higher concentrations of calcium in the wine would be obtained. Filtrations of three 11,000-gallon tanks of sauterne wine, through pads similar to sample 11 (Table 11) were made. The original calcium content was 21 p. p. m, and, after filtration and segregation of the first 500 gallons of each run, the calcium contents were 75, 76, and 88 p. p. m., respectively. Several similar filtrations were made with pads like sample
Iron and Calcium Pick-up from Diatomaceous
Silica Filtration The greatly increased use of chamber types of filters employing either metallic screen or cloth filtering medium supports with a diatomaceous silica filter aid has been of considerable advantage to the wine maker for filtering cloudy wine>which would soon stop the operation of filters with other types of filtering media. In addition to a greater effectiveness and economy of filtration, increased sanitation has been obtained. Therefore, some observations have been made on their use with nine.. As with other filtering media, it has been observed that, in general, considerable variation occurs between the different filter aids and in their effect on wine. Further, for a given filter aid, the effect varies with the wine being filtered. In filtration practice in wineries, usually the precoat of filter aid is applied a t the rate of 5 to 10 pounds of the filter aid per 100 square feet of filtering surface. This is the practice when using the pink calcined filter aids. Frequently when a very cloudy mine with a high content of suspended solids, such as a new sweet wine, is t o be filtered for the first clearing, a precoat of one of the white calcined filter aids is used. Such a precoat may consist of as much as 15 pounds of filter aid per 100 square feet of filtering surface. For the actual filtration of very cloudy wines, 10 to 15 pounds of filter aid are used per 1000 gallons of wine; for wines that are only slightly hazy or that have been previously clarified by fining with gelatin, isinglass, or bentonite, usually only 5 to 10 pounds of filter aid per 1000 gallons will be required.
NOVEMBER, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
Examination of many wines filtered with diatomaceous silica filter aids has demonstrated that there may be a limited amount of iron and calcium removed from the filter aid; as in the case of certain asbestos pads and aqbeqtos fiber pulps, such iron and calcium may contribute to a hazing or clouding if only small volumei of' wine are segregated during the initial stages of filtration, as immediately after precoating. If thi. is avoided by filtering relatively large volume.: of w n e a t one time, tlie iron and calcium pick-up is negligible nith the better quality filter aids. As typical examplei, two wines. a sauterne and a muscat, niay be conqidered. Befor61 filtration, the sauterne contained 4 p. p. m. of iron and 64 11. p. m. of calcium; after filtration it contained 4 p. p. m. of iron and 67 p. p. m. of calcium. Before filtration the muscat contained 6 p. p. m. of iron and 73 p. p. m. of calcium; after filtration it contained 6 p. p. m. of iron and 76 p. p. m. of calcium. Each of these filtrations was with a n 11,000-gallon volume of wine, using 8 pounds of a standard commercial pink calcined filter aid for each 1000 gallons of wine. Observation of these wines after tank storage for 60 days indicated no cloudirig or sediment formation. They were then bottled and after 8-month storage were still brilliantly clear. I n another plant using filter aids from different natural deposits, observations were made on the filtration of two 8000-gallon tanks of it Riesling wine which before filtration contained 13 p. p. m. of iron and 31 p. p. m. of calciuni each. This mine previously had been clarified with gelatin and was clear a t the time of filtration. One tank was filtered with a n air-dried white calcined diatomaceous silica while the other was filtered with a pink calcined product. After filtration the first tank of wine had iron and calcium contents of 17 and 38 p. p. m., rekpectively. Similarly, the second wine after filtration contained 17 p. p. m. of iron and 80 p. p. m. of calcium. On standing 60 days, unfiltered controls showed a slight hazing and ferric casse. In the same time the filtered wine in both tanks becaine cloudy and a heavy deposit was formed on the tank bottoms. As a consequence of these varied plant observations, a study was made of thirteen filter aids obtained from California, Oregon, and Utah diatomaceous silica deposits, representing the standard commercial grades of refined natural, pink calcined, and n-hite ralcined filter aid products. Laboratory evaluation of the iron and calcium pick-up from these samples by vine was made by slowly stirring a given volume of wine containing the filter aid for 30 minutes arid rapidly filtering through filter paper. To each 100 cc. of wine, 0.1 gram of filter aid was added. Only clear wines were used so that the total time for filtration would be a t a minimum and not to exceed fifteen minutes. Duplicate filtrations using vacuum and reducing the filtration time to 5 or 7 minutes indicated that there was little if any difference in iron or calcium content as compared to filtration during 13 minutes without vacuum, when there had been a n initial 30-minute period of slow mixing of the wine and filter aid. The data from these tests are presented in Table 111. I t is evident from this information that there is considerable variation in the effect of the different filter aids on wines and that as a result these effects should be known definitely by the wine maker when a choice of filter aid is made. On the basis of these observations, such filter aids as 1, 2, 9, 10, 11, and 12 would appear more suitable for general winery use. Such filter aids are the ones being most generally and successfully used. Information on the relation of the filter aid not only to the filtered wine but also to the sediment formed was secured with two wines of Riesling type. Three portions of each wine were filtered using, in turn, a standard pink calcined product, an acid-washed pink calcined product, and a standard white calcined product. Samples of 500-cc. volume were used for iron and calcium determination. These samples m-ere stored
1249
TABLE 111. I R O N AND CALCIUM PICK-UP BY W I K E FROM V.4RIOUS DIATOMACEOFS SILICAFILTER AIDS (IN P. P. M.) Filter Aid" Control 1 2
Riesling 1 Fe Ca
Sauterne 1 Fe Ca
Sauterne 2 Fe Ca
Chablis 1 Muscat Fe Ca Fe
7 57 48 19 71 9 64 53 28 85 9 66 58 34 81 3 9 74 63 26 83 4 9 60 59 33 80 5 10 65 57 29 79 6 8 63 7 68 9 40 6 8'3 3 7 7 4 51 4 40 5 71 4 59 a 11 70 4 66 3 35 5 77 4 9 66 4 18 4 78 5 9 4 55 10 8 63 4 61 3 25 5 76 5 11 9 5 25 4 77 5 66 5 64 12 8 65 4 64 4 30 5 76 5 13 9 i9 5 76 8 50 5 92 5 a Samples 6, 8, and 13 s e r e natural products: 1, 4, 9, and 10, pink calcined products: 3, acid-uashed pink calcined product: 2, 5 , 7, 11, and 12, u hite calcined products.
for 8 months, during which time heavy sediments had developed. For analysis, 400 cc. of the clear supernatant wine of each sample were carefully removed by slow siphoning, and the sediment and remaining 100 cc. of wine were then vigorously shaken. Iron and calcium determinations were made on aliquots of these eight subsamples. The data are recorded in Table IV, and it is evident that, with the possible exception of the filtration with the white calcined diatomaceous silica, there is no significant accumulation of calcium in the sediment from these wines. With Riesling 2 wine there is not only an apparent increase in iron content of 1 p. p. m. with the use of the filter aids, but there is a distinct increase in the amount TABLE IV. Wine
RELATION OF FILTER AID TO SEDIMENT FORMATION Filter Aid
400-Cc. Sample Fe Ca 7 -
Riesling 2
Riesling 3
Control Pink Pink acidwished White Control Pink Pink, aciduashed White
11 12
100-Cc. Sample Containing Sediment 500-Cc. Av. Fe Ca Fe
Parts p e r million 12 53 56 13 54 54
.
11.2 12.2
12 12
56
50
14 15
53 55
12.4 12.6
8 10 10
55 55 57
10 13 16
55 56 54
8.4 10.6 11.2
10
51
14
56
10 8
of iron associated with tlie sediment. With Riesling 3, this same trend is even more pronounced. With wines of this type it is therefore evident that there may not be marked increase in calcium content, although relatively larger increases in iron content ma.; occur and such increases may be associated with sedimentation and therefore niay be a causative factor. Such information is desirable when selecting an appropriate filter aid, or when attempting the elimination of sedimentation problems resulting from a n improper use of such filter aid. In general the use of selected diatomaceous silica filter aids will result in relatively small and unimportant increases in the iron and calcium content of wines. However, the effect of each filter aid should be determined with the particular wine being filtered if clouding or sedimentation occurs after such filtration.
Removal of Microorganisms from Wine b y Filtration The removal of microorganisms from lvine by filtration has been accomplished to varying degrees by several types of filters now on the market ( I ) . Incubation tests, microscopic observations, and chemical analyses hare shown that, on a commercial scale, filtration using certain filtering materials may be used to secure complete removal of tournt and acetic acid bacteria, yeait, and certain other organisms found in
INDUSTRIAL AND ENGINEERING CHEMISTRY
1230
wines. It has been observed that such filtrations were secured when using porous silica candle filters with candles of h e porosity; with pad filters using pads like samples 1, 2, 3, 4. 7, 12, 13, 14, and 16 (Tables I and 11); and with certain chaniber types of filters using filter aids like numbers 1, 4,6, and 8 (Table 111). In addition, a special filter aid similar to number 4, but giving a somewhat tighter filtering medium, resulted in probably the most satisfactory filtrations of this type yet obtained. As a result of the microscopic observations of over one hundred different commercially filtered but nonpasteurized wines, it was found that, when the filtration was with one of the filtering materials mentioned, complete removal of the microorganisms was effected and pasteurization was not required for their control. In certain additional cases, it was observed that, while removal of the microorganisms was obtained by filtration, a reinoculation was secured by placing the wine in nonsterile containers. This only emphasizes the need and desirability of maintaining the advantages of removal of microorgani3ms by ordinary filtration practice. Frequently it has been observed that certain previously clarified and stabilized wines nevertheless became cloudy and deposited sediment even though there was no measurable increase in iron or calcium content. Dry wines of the Haut Sauterne and ChDteau Yquem types have been more common in this respect, with sauterne, Chablis, and Riesling to a less extent. Of the fortified wines occasional trouble has been experienced with angelica and muscatel types. I n many such cases microscopic observation demonstrated that the sediment was not amorphous and from the precipitation of colloidal materials, nor were crystalline materials such as tartrates present. Rather such sediments were usually white or gray in color and were composed practically entirely of microorganism cells. The occurrence of certain types of yeast cells particularly was noted. In the majority of such cases of clouding and sedimentation, the cellular deposits were nearly free of amorphous substances. Microscopic examination of the sediments resulting from centrifuging portions of such cloudy wines demonstrated the presence of microorganisms similar to those found in the naturally formed sediments. These cloudy wines have been filtered with chamber-type filters using the special filter aid previously mentioned. Samples in sterile bottles of such filtered wines and of the corresponding unfiltered cloudy wines have been held a t room temperature for 8 months, Over 90 per cent of the unfiltered samples became more cloudy with varying but increasing amounts of sediments formed. Microscopic observations demonstrated the sediments to consist of the typical microorganism forms. Similar observation of samples of the filtered wines indicated that the originally contaminating microorganisms had been removed, and that no clouding or subsequent sedimentation developed, the wines remaining brilliantly clear.
Literature Cited (1) Cruess, W. V., Fiuit Products J.,14, 198-200 (1935,. ( 2 ) Saywell, L. G., IND.EXQ.CHEV.,26, 951-2 (1934). (3) Saywell, L. G., Deutschman, W. A , , Cunningham B B , unpublished data. REOEIVED September 24. 1935.
VOI,. 27, NO. 11
Volatile Acids of Wine )LARK M. 3lORRIS Concannon Vineyards, Livermore, Calif.
Many volatile acids in addition to acetic were reported by early workers but their presence was not confirmed by more recent investigators. It was found that sound wines contained acetic and traces of propionic acid. Diseased wines contained acetic with traces of formic acid. Little or no lactic acid was found. Older wines seem to contain acetic and traces of propionic acid. Young wines appear to contain nearly all acetic acid.
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OLLOWING the report by Declaux in 1865 that volatile acids other than acetic were present in wine, the volatile acids present were investigated by a number of authors. The following acids are reported as being present in the steam distillate of wine: Acetic ( 2 , 4, 7, 8,1 4 , I S , 17, 18, 19, 2 5 ) Formic (14, 43, 1 5 )
Carbonic (8) Propionic (1 8 16 18 26’
Butyrjc (la,’4,’8, iL, iY, is,2 5 ) Caproic (8) Capric (8) Caprylic ( S j
Benzoic (11) Lactic Salicylic ( 6(, I13, I j 15, f 7) Oenanthic (8) Tartronic (@a, Valerianic I S) 15) Lauric ( 8 ) Valeric ( 1 1 )
Of these, acetic, formic, propionic, butyric, and lactic are more commonly reported in the early literature. It is believed that the volatile acids of sound wines consist largely of acetic with small amounts of propionic (2, 8, 16, 18, 25), and that in diseased wine3 larger amounts of propionic acid are present together with traces of butyric. Declaux reported that in diseased wines there is a decrease in fixed acids and an increase in volatile acids; part of the volatile acids are derived from the fixed. With increase in volatile acids an increase in butyric acid occurs; as high as 0.025 gram of butyric acid per liter was reported by Declaux. However, most of the studies were of a qualitative nature and the quantitative procedures, where used, were of questionable accuracy. Furthermore there is no unanimity of opinion as to the nature of the volatile acids present in sound and diseased wines. Therefore an investigation of the nature of the volatile acids of California wines was made and the results of this study are reported here.
Determination of Volatile Acids The procedure used was essentially that of Dyer (3) and Declaux (2) : Enough wine to contain about 0.5 gram of total volatile acid was distilled to one-tenth of its original volume. Some difficulty was experienced in removing all of the volatile acid. The distillate was exactly neutralized with 0.1 N sodium hydroxide to phenolphthalein and evaporated to less than 100 cc. The
