UNIVERSITY OF CALIFORNIA 
 
 AGRICULTURAL EXPERIMENT STATION. 
 
 BULLETIN NO. 63. 
 
 Experiments on Methods of Fer- 
 mentation. 
 
 determination of the effect of various methods 
 of fermentation upon the resulting wines, a 
 series of experiments with one and the same 
 
 No. 558. Masn put in in three successive por- 
 tions, kept separate by a lattice framework wedged 
 in place, thus forcibly keeping the pomace sub- 
 
 merged and divided into three separate portions— 
 
 In view of the great interest attaching to the according to Perret s system; the uppermost frame 
 
 being about two inches below the surface of the 
 must before fermentation. Tank covered. 
 
 No. 559. Mash put in at once and the pomace 
 kept submerged about two inches by means of a 
 , single Perret's frame, as practiced to some extent 
 kind of grape, treated differently both in respect at Fresno and elsewhere; no cover, 
 to temperature and the appliances used, was No. 560. Mash left uncovered aad subjected to 
 carried out at the Viticultural Laboratory with Sequent « foutage" or stirring, at least three times a 
 
 day, during fermentation; a common French and 
 
 the results given below. 
 
 These experiments were all conducted within 
 the limits of temperature adapted to '* high fer- 
 mentation," since the question of how best to 
 manage the fermentation at the prevailing vin- 
 tage temperature of California is the one hav- 
 ing the greatest practical interest. As no means 
 were at hand for maintaining a temperature suf- 
 ficiently low for 94 low fermentations," proper, 
 these were omitted, but it is intended to ar- 
 range for such experiments next season. 
 
 It should be distinctly understood that these 
 few experiments were selected from the large 
 number of possible ones, in order to test the in- 
 
 Californian practice, 
 
 No. 561. Mash covered with a "floating cover," 
 rising and falling with the pomace, any from on up- 
 per side being washed off; stirred three times a day; 
 a French method, and adopted at the Viticultural 
 Laboratory. 
 
 No. 563. Grapes put in whole, stems and all, to 
 be gradually crushed by means of a cross-peg 
 stirrer, used energetically three times a day; no cov- 
 er. A Burgundy method, used at several California 
 wineries; known as " Morel process. " 
 
 No. 564. A tub charged with about 140 pounds 
 of mash, and then left to itself, cap, vinegar-flies and 
 all; without stirring or cover; the old Californian, or 
 "go-as-you-please," method. 
 
 (C ) In the cellar of the laboratory kept at 
 
 fluence of certain conditions upon the composi- steady temperature of 62 degrees, 
 tion and quality of red wines, so as to deduce No. 562. Fifty -gallon tank charged like the rest 
 therefrom principles that shall apply to large with 230 pounds of grape mash, provided with a 
 -as well as small-scale practice, when allowance 44 floating cover," and stirred three times daily, 
 is made for the known difference of ciroum- l n a ll cases the temperature was ascertained 
 stances m each case. • . . thrice daily; during the hight of fermentation 
 .^^^ T^^ 6 * VeryK ?°^ art f lC i e K° f every few hours; and in the tanks provided 
 second-crop Zmfandel, courteously donated by with ' framea the ^mperature of the top liquid, 
 Mi J Gallegos of Mission San Jose About and of the pomace beneath each frame, was taken 
 SSflr ? one-sixth tons were sent, in University 8epara tely in order to follow the exact course 
 t^n f e h a K 8, . The y arrive f d k ^exce entcondi- of ^ ferm ^ tation g . u OD8erva tions were 
 £?«h« n^f Wer8 K r ! th 5f Bma ! 1 1 aild th A & made every morning in the tanks subjected to 
 t£ta ^« qn H e ?' f' * horo K u 8 h jy f 80U °^ stirring, so as to ascertain the temperature of 
 o«mnn£ f C f fr e ?V nd ]UlCG f ' T the *°P b ^tom layers of the pomace cap 
 composition of the latter was as follows : formed during the ni R ht, and that of the liquid 
 
 Solid contents by spindle 21.05 beneath. 
 
 Sugar by copper test 19.75 The details of the fermentations, however in- 
 
 V^ c ' d °5 structive, are too lengthy to be given in this 
 
 sn 2 7 place, and will be found fully recorded in the 
 
 Nine different samples were fermented, un- forthcoming report for the year 1886. It need 
 der the following conditions- ° n *y be said that while No. 556, fermenting at 
 
 . T . - _ _ 100°, went dry within 48 hours, No. 562, at 62°, 
 
 (A.) In a hot chamber kept at a temperature required ten days. Of the rest, No. 560, the 
 
 ^t^s^r^i^ £? 5££ t °r ta h Dk su , bjec ^ to ^ u n sti r g ' weut 
 
 open in the tub; the other (No. 556? covered with a throu g h most rapidly and energetically. 
 '* floating top" that rose and fell with the pomace, Composition of the Wines. 
 
 ^^fcS 0 ^- B ^ were subjected Th , table ^ow .how. the composition of 
 (B.) I? a room kept at a temperature ranging *be wines resulting from the several fermenta- 
 frora 72 degrees to 75 degrees: five 50-gallon tanks, * 10ns - The y were aI1 analyzed, and their color 
 each charged with aoout 230 pounds, nearly filling determined, within a few clays after pressing, 
 the tanks, and arranged as follows: *he murk being filtered for the purpose. 
 
Os On On Ov 0\Ln Lrx Ln Ux 
 to 4* vjO h C MD OO-O 0\ 
 
 hi «-i EL ~ 70 ;? f- E- 
 
 C5 v< ~crq orq Q " TO OQ 
 
 rt cT - P "0 ^ S* P 
 
 3 3 < i 
 
 ro fc g • 5F 
 
 3 P Q c. 
 
 a> g o 3 
 
 330^3 
 
 o < . 33 < 
 
 33 3 • C. . 
 
 vO 00 00 vO vO vO vO vO vO 
 
 .10 »to B Q Q QU}4 > 
 
 CjO 4- 4- to U) 4i 4* 
 4*. CT\*0 "O Osvj O WCa 
 
 M Q\ ps Q 4*. 00 Q .k 4a. 
 
 CO 
 
 ^Spav ^a 
 
 ■oi.TBj.rej, SB ppy 
 
 •aruuBx 
 
 •Xjisuajuj 
 
 As regards, first, the alcoholic contents of the 
 several wines, it will be noted that the same 
 percentage was obtained in six out of the nine 
 while three, viz., Nos. 559, 563 and 564, cor- 
 responding respectively to the single-frame, 
 Morel, and "old-style " processes, show a de- 
 ficiency which does not differ widely for the 
 three, being not quite one per cent. 
 
 In the single-frame process, a relatively thin 
 layer of liquid was exposed to the air, constant 
 ly agitated by the gas coming from below, and 
 heated by its position just over the hot cap, 
 The alcohol simply evaporated from this iso- 
 lated portion of the wine, and (where this mode 
 of fermentation is practiced on the large scale I 
 have sometimes found this layer so warm that 
 toward the end of the fermentation the bulk of 
 its alcohol was gone and it had a vapid, flat 
 taste, often more of vinegar than of alcohol. 
 
 In the case of the old-style process, also, it is 
 «asy to see where the loss of alcohol occurs. It 
 is here the hot pomace cap, offering a large sur- 
 face to the air and kept drenched with the fer- 
 menting liquid by the bubbling up from below, 
 which assists the evaporation. That the latter 1 
 
 is accompanied by its transformation into vin- 
 egar is apparent to the nostrils so soon as the 
 first violent stage of the fermentation is past. 
 
 In the case of the M Morel process," the 
 cause of the loss of alcohol is not so obvious. 
 It must be partially accounted for by the 
 abundant stirring and high temperature; but 
 it is possible that from sonie cause a part of 
 the sugar may have been converted into some 
 other compound than alcohol. 
 
 A somewhat unexpected result is the fact 
 that the two hot fermentations (556 and 557) 
 yielded the same amount of alcohol as those 
 fermented at a much lower temperature. The 
 obvious explanation is, that the short duration 
 of these fermentations balanced the influence 
 of the high temperature as compared with those 
 in the slower fermentations, in which the op- 
 portunity for evaporation lasted longer. It 
 will be highly interesting to compare, hereafter, 
 the other products formed alongside of the al- 
 cohol in the three sets of fermentations. 
 
 As regards, next, the acid of the several 
 wines, it is not unexpected to find that the 
 open foulage, No. 560, on the one hand, and 
 the Morel process on the other, have given the 
 highest figures; the one because of the constant 
 access of air, the other from the same cause, in 
 addition to the extraction of acid from the 
 stems. 
 
 The lowest figure for acid (.49) is given by 
 Nos. 556 and 558, the hot fermentation with 
 cover, and by the one with the three submerged 
 frames. In the case of the latter this was to 
 be looked for, and is precisely one of the chief 
 advantages claimed for Ferret's method. In 
 the case of the former it is somewhat unexpect- 
 ed, and is the more instructive in contrast to 
 No. 557, the hot fermentation in which no 
 cover was used, and in which the acid is one 
 pro-mille higher. Almost precisely the same 
 difference occurs in the fermentations made at 
 the lower temperature, one with the floating 
 cover on (No. 561), and the other (No. 560) 
 without cover. The beneficial influence of the 
 cover in preventing the formation of acid dur- 
 ing fermentation is therefore placed beyond 
 question. 
 
 It should, however, be added, that in none 
 of the fermentations made, there is at this time 
 (Nov. 24) a notable amount of volatile (acetic) 
 acid. This is true even of No. 564, the " old- 
 style " one, in which the odor of vinegar was 
 abundantly obvious before pressing. It shows 
 the odor of vinegar plainly in boiling, but the 
 amount is at present less than five thousandths 
 of one per cent. 
 
 It is'somewhat remarkable that the fermen- 
 tation No. 562, made at the lowest temperature, 
 should yield a relatively high proportion of 
 acid, exceeding that found in the fermentation 
 made under the same conditions at a higher 
 temperature. Whether this is to be accounted 
 for by the longer duration of the low-tempera- 
 ture fermentation, remains to be investigated. 
 
Considering, next, the matter of tannin, we 
 note at a glance the influence of the high tem- 
 perature in aiding a complete extraction. The 
 two hot fermentations, Nos. 556 and 557, have 
 given the maximum of tannin, despite .their 
 short duration; more even than in the case of 
 the tank with diligent open foulage, and as 
 much as the Morel process, stems and all, 
 which was continued for 11 days; the effect in 
 this case is so marked as to leave no doubt of 
 the influence of this factor, and in it lies, prob- 
 ably, at least a part of the explanation of the 
 fact that the hot parts of our State have yield- 
 ed more ftannin in their red wines than the 
 cooler ones. 
 
 The two tanks in which the frames were used 
 (Nos. 558 and 559) present a curious problem. 
 In both cases the same amount of tannin was 
 taken up, although in the one the pomace was 
 in a solid mass, and in the other was kept dif- 
 fused all through. The result is disappointing 
 as concerns the three-frame process, and shows 
 clearly why, despite its apparent advantages, 
 this method of treatment has not been widely 
 adopted, even in France. It is evident that 
 simply keeping the pomace in the liquid cannot 
 replace the grinding and disintegrating action 
 of the direct stirring or Joulage, so far as the 
 extraction of tannin and color are concerned; 
 for a glance at the color column shows that the 
 deficiency of tannin is accompanied by a simi- 
 lar relative deficiency of color, as compared 
 with the tanks that were stirred. The 6ame 
 holds of the single-frame fermentation, where 
 the color is even less; and the fact that an even 
 amount of tannin was extracted, notwithstand- 
 ing the pomace was in a solid mass at the top, 
 is explained by the high temperature which, as 
 the record shows, prevailed in that cap. The 
 same consideration doubtless applies to the 
 "old-style" (No. 562), in which the high tem- 
 perature of the pomace cap offset the lack of 
 stirring, and both tannin and color were fully 
 extracted. 
 
 A singular and unexplained fact is the defi- 
 ciency of tannin in the tank with open foulage, 
 without cover, for which no obvious cause can 
 be assigned; the duplication of the determina- 
 tion, however, leaves no doubt of the fact, which 
 can hardly be explained without assuming that 
 some of the tannin at first extracted was subse- 
 quently destroyed by the action of the air. If 
 this were so, the full complement of tannin in 
 the " Morel " product might be explained by 
 the presence of the astringent stems. 
 
 The column giving the color-intensities is 
 very instructive also. It will be seen that those 
 yielding a low color were the two tanks with 
 frames, already discussed, and the low-tempera- 
 ture fermentation, No. 562, in which, despite 
 
 diligent stirring, and the pretty full extraction 
 of tannin, that of the color remained incom- 
 plete, being nearly one-third less than the 
 maximum. 
 
 The full discussion of the bearings of these 
 fermentation experiments is perhaps best de- 
 ferred until' the development of the wines, and 
 their full analysis in their more advanced con- 
 dition, shall give more data in regard to the 
 final results of the several treatments. Those 
 familiar with the subject of fermentation may, 
 however, already derive important lessons from 
 what is recorded above. Of course, these re- 
 sults must be verified by repetition the coming 
 season, before they can be accepted as maxims; 
 but there is much that cannot well be upset by 
 any subsequent experiments. Among the 
 points that may be considered well settled is 
 that the method of fermentation adopted by 
 this department (viz.: floating cover, with 
 thrice daily stirring,) is amply justified by the 
 outcome of the nine fermentations. It secures 
 all the advantages of aeration, full extraction of 
 tannin and color, and maximum of alcohol, 
 without any risk of acetification if properly 
 managed. The method has been carried out on 
 the large scale by Mr. John Gallegos for two 
 years past, and has yielded excellent results; 
 the only difficulty encountered being that in 
 the case of very soft-skinned grapes, the fre- 
 quent stirring reduced them to a pulp which it 
 was difficult to press. In such cases the stir- 
 ring must be moderated and made with imple- 
 ments having the least crushing effect; but I 
 am satisfied that in the hot vintage climate of 
 California, the leaving - open of fermenting 
 tanks to the access of air is most objectionable, 
 is one of the most common and prominent 
 causes of unsoundness, and should be done away 
 with universally, adopting either the use of 
 floating covers, or at least a cover over the top 
 of the tank. Whether the disadvantages of 
 the single-frame system can be overcome by a 
 repeated pumping-over of the liquid from below 
 over the pomace, is a question yet to be deter- 
 mined; but that in the use of this method there 
 is always a serious loss of color and tannin, can 
 hardly be doubtful. 
 
 Regarding the quality of the wines resulting 
 from the several processes, but little can as yet 
 be definitely said. However, the unanimous 
 verdict of those who have thus far tasted them 
 is to the effect that the product fermented at 
 62°, though light-colored, is the best, and that 
 rushed through within 48 hours beyond com- 
 parison the poorest, being flat and without 
 character. Time alone, however, can definitely 
 determine the ultimate outcome. 
 
 E. W. HlLGARD. 
 
 Berkeley, Jan. 6, 1887,