UNIVERSITY OF CALIFORNIA agricultural Experiment Station College of agriculture e. j. wickson, act. ng director BERKELEY, CALIFORNIA CIRCULAR No. 23 (August, 1906.) PURE YEAST IN WINERIES. BY FREDERIC T. BIOLETTT. While in the present state of the wine-making industry and of the general lack of knowledge among wine makers of the principles of fermentation, the use of pure yeast is not to be universally advocated, there are many cases in California where it can be of great utility. Both laboratory and cellar experiments on a sufficiently large scale, and continued for a sufficiently long time, have fully demonstrated that most excellent results can be obtained by the use of pure yeast. This is especially true as regards white wine. The principal benefits to be obtained at present are a thorough fermentation, a rapid clearing and an absence of the disagreeable flavors of secondary fermentation, which are only too common in many of our Californian wines. These benefits are to be obtained, however, in cellars only where especial care in the ordinary processes of wine- making are at present practised. In many of the larger wholesale wineries, or in those where ordinary carefulness is not exercised, little benefit would result from the use of pure yeast. There are other much more important reforms to be introduced first. The great improve- ments in methods which have been introduced in late years in certain large wineries, however, make it probable that before long many of them will be in a position to make use of the advantages of pure yeast. For this reason it is advisable that the methods of handling pure yeast practically in wine-making should be made familiar to the wine- makers of small cellars where it is at present feasible. This circular is issued, therefore, with the hope of interesting some of the more progressive wine-makers in this method of improving their product. It should be clearly understood at the beginning that the purity of the yeast is of less importance than its character. The yeast must be of the right kind. Beer yeast will give a flavor of beer, and will, moreover, fail to transform all the sugar, leaving a half fermented liquid that will inevitably spoil. Bread yeast, apiculate yeast, any of the innumerable species of yeast that occur in fermenting liquids, will simply injure the wine. Even the true wine yeast has many varieties, each with its own qualities, and it is unsafe to use any pure yeast until it has been properly tested for the purpose contemplated. The yeast must be obtained, therefore, from a perfectly reliable source, where it has been proved suitable for the conditions in which it is to be used. An unsuitable or untested yeast is as sure to give unsatis- factory results in the fermenting vat as a lot of seedlings in the peach orchard. On the other hand, the best results are to be obtained only if our original stock is perfectly pure. If the stock is contaminated with vinegar germs, wine-flowers, or molds, it may do more harm than good. The effect would be similar to that obtained by planting wheat seed mixed with cheat or alfalfa seed with dodder. For these reasons the Experiment Station has selected and tested a number of yeasts which have been under observation for several years, and is ready to recommend one for use in practice which has uniformly given good results. We are prepared to supply small quan- tities of this yeast in an absolutely pure state to a limited number of wine-makers for use during the present season. If the directions of this circular are carefully followed, good results will be obtained, provided nothing is done to counteract them. Pure yeast, however, will not overcome altogether the effects of infected vats and casks, nor will it enable the wine-maker to produce Chateau Lafite from raisins, and above all, it will not aid him in the vital point of cool fermentation. If, however, the usual precautions known to all good wine-makers are taken, pure yeast will give satisfactory results. The principal things to be kept in mind are to get the grapes or must into the vats as clean as possible, to introduce the starter before any spontaneous fermentation has started, and to control the tempera- ture. For red wine some such cooling device as that described in Bulletin 174 should be used, unless very small vats are employed and the fermentation is to take place in the cooler sections of the State. Pure yeast is particularly valuable when used in connection with the method of making red wine described in Bulletin 177. For white wine good results will be obtained in almost all cases, though a preliminary defecation is desirable. This defecation may be obtained by the use of sulphur fumes or of meta-bisulphite as described in Circular No. 22. The small quantity of pure yeast received must be increased by the wine-maker until it is sufficient for a "starter." A starter is a quan- tity of must containing young, vigorous yeast in sufficient amount to take possession of the vat of grapes or cask of must before the germs naturally existing there have time to develop. The method of making this starter is described later. This starter must be relatively pure. It is always used when in full fermentation, that is, when it contains the maximum number of pure yeast cells and before the weakening of the yeast has allowed any bacterial or other spores that may be present to develop or in- crease. The few foreign germs, therefore, which may get into the starter during the last manipulations may be disregarded, as they are in such an infinitesimal minority that they have no chance to develop sufficiently to do any harm before the wine is finished and safe from their attack. With ordinary care in the manipulation of the starter they will be incomparably less numerous than the same germs existing naturally in the crushed grapes to which the starter is added. The amount of yeast added must be sufficient. As a rule the amounl of starter should be about 1% of the volume of the grapes or must to be fermented. If the grapes have been partially sterilized by heat or the must by defecation, less will be sufficient. If they contain considerable amounts of natural germs, more will be needed. If the infection with molds, yeasts and bacteria due to bad grapes, unclean crushers or unsound vats is considerable no practical amount of pure yeast will have any effect. The addition of too large a volume of starter should be avoided, as it may produce too rapid and violent fermentation, which will be difficult to control even with cooling machines. While the perfect sterilization of the grapes and must is at present impracticable and unnecessary, the number of foreign germs present should be kept as low as possible. Sufficient freedom from such germs is obtained in the manufacture of white wine by settling, sulphuring, or other means of defecating the must. In the heat-extraction method of making red wine (see Bulletin 177) the partial sterilization due to the heating accomplishes the same end. With the ordinary method of making red wine this end can be compassed only by the most minute attention to cleanliness and other means of preventing the entrance of undue numbers of germs into the crushed grapes. If grape boxes, crushers, carriers, pumps, chutes and vats are never washed and are coated with must and grape skins, they serve as propagating grounds for yeasts and germs of all kinds. Piles of dry pomace outside the cellar or scattered on the surrounding roads, supply the air with myriads of bacterial spores. Vats of grapes exposed to these agents of infection cannot be influenced by a few buckets of pure yeast. Directions for Use of Pure Yeast. For 1000 gallons of crushed grapes or of must. Materials needed : 1. — A 3-oz. flask of pure tested wine yeast. 2. — Half a gallon of sterilized must, about 10% Balling, in a one- gallon demijohn. 3. — Ten gallons of defecated must in a 25-gallon tub furnished with a good cloth cover. 4. — A room comparatively free from dust. (For example a moist cellar. ) Method of Procedure. First Day. — Squeeze out a quart of must from clean, fresh grapes. The grapes should not be over-ripe. Mix the must with a quart of boiled water and place the mixture in a sterilized one-gallon demijohn. The demijohn should be sterilized by thorough cleaning, and heating for an hour in an oven or rinsing with a pint of 10% sulphuric acid and final rinsing two or three times with boiled water. After placing the diluted must in the demijohn close the latter with a firm plug of cotton wool (surgeon's cotton). Place the demijohn in a deep covered pan containing water such as an ordinary kitchen wash boiler and heat to boiling for one hour and then put aside to cool. Do not remove cotton plug. Second Day. — 1. Pour a few drops of alcohol onto the cotton plugs and necks of the pure yeast flask and the must demijohn and im mediately set fire to the alcohol. This will destroy any spores which have settled with the dust on the plugs and necks. After shaking the pure yeast flask thoroughly pull out v the plug and pour the contents into the must demijohn. Replace the plug of the demijohn and shake for two minutes in such a manner as to aerate the must. Repeat this shaking three times a day. Place the demijohn in a warm room where the temperature varies as little as possible. 2. Defecate 10 gallons of must from clean, fresh grapes containing not over 22% Balling. The most convenient method of defecation is by the use of the sulphur tapes commonly used in cellars. In a 12 to 15 gallon keg burn as much sulphur as the air present will consume. (This is about J of an ounce.) Then pour about 4 gallons of perfectly fresh must into the keg, bung up and roll for 5 minutes to make the must absorb the sulphur fumes and finally fill the keg with must, taking care to mix the treated with the untreated must. This will prevent any com- mencement of fermentation for two or three days, if the must is kept in a fairly cool place. Chock the barrel so that it will remain steady and allow the impuri- ties of the must to settle. Third or Fourth Day. — In from 48 to 72 hours the must in the demijohn should be in full fermentation and the must in the barrel should be perfectly clear. Draw off the clear must, with a hose steril- ized in hot water, into the 25-gallon tub which should also have been well scalded. Pour the fermenting must from the demijohn into the must in the tub and thoroughly aerate the mixture by dipping out some of the must with a quart dipper and pouring through the air back into the tub. This should be repeated three or four times a day, or oftener if fermentation is slow in starting. Fifteen or twenty quarts should be poured over in this way each time. The tub of fermenting must should be kept in a warm room as free as possible from draughts and dust. It should be kept carefully cov- ered between the aerations, to exclude dust. Sixth or Seventh Day. — In from 48 to 96 hours after starting, the must in the tub should be in violent fermentation, and is then ready to use to start the regular fermentations. The volume of starter used should be about 1% of the volume of the grapes or must to be fer- mented. If used for white wine, simply pour the proper quantity of starter into the cask before pumping in the must. If used for red wine, the starter should be distributed through the vat of crushed grapes by pouring in a little at a time as the vats are being filled. If it is desired to ferment more than a thousand gallons with pure yeast, special directions will be furnished by the Station on request. Very satisfactory results can be obtained simply by starting new vats or casks with 1% of fermenting must from one of the first fermenta- tions, which have been started with pure yeast, when it is in full action.