Patented July 30, 1929. l@722-9858 UNITED STATES. PATENT OFFICE. ISED.U"SO.HO.V]?, OF lqEW YORK, N. Y., ASSIGNOR TO THE PLEISC'RXANN COMPANY, A CORPORATION OF OHIO. KETHOD OF YEAST PRODUCTION. No Drawing. Application filed Tanuary 19, 1922. Serial ITo. 530,4". Heretofore, in the fermentation industries where, solutiORS containing sugars have been subjected to the action of yeast, either for .the production of yeast as a nmin produet or for the production.of alcoholic hquids as the main product (with or without recovery . of yeast as an additional product), it has been regarded that both carbon dioxide and ethyl alcohol were ultimate products of yeast lo action and, in the yeast-production industry, it has been considered advisable not only to remove carbon dioxide from the fermentation zone wherein the yeast was grown, in order to prod ce high yields of yeast, but also to 15 conduct the . yeast growth in a liquid iautrient solution in which the alcohol content was as low as possible, the alcohol being regardexl a.9 a by-product of yeast growth or metabolism and, as such, not only as being of no 20 nutrient value to the yeast but as actively detrimental when present in any considerable amount in the yeast-nutrient solution. In the manufacture of bakers 5 yeast by th'e usuauy so-caued "aeration" pr.ocess, one 25 advantage (from the standpoint of yeast growth) hitherto generahy regarded as inherent in the blowing of large amounts of air throbgh the solution in which the yeast is growing has been the elimination of alec@- 30 bol either from the entire body of the yeastnutrient solution itself or at least from the immediate juxtaposition to the exterior surface of the cells of the yeast, individually considered, suspended in the aerated solu35 tion. At best the alcohol produced in sacchariferous solutions incidental to yeastgrowth (as regards the effect of such alcohol upon the yi--ast cells present) has been regarded as a substance which m' ht b6 tolerklfl limits but 40 ated by the yeast within va-riab e in no event having any directly beneficial effect upon further yeast growth itself. I am aware of the process proposed by Friedrich Hayducl@ in German Patent No. 45 3006627 in which reference, is made to utilizat.ion of alcohol as a nutrient by the yeast, but I.U the process as referred to in this German patent -and in ony similar processes which, may have bee@ here-tofore carried crut, the 50 object sought and ihe feature emphasized as ng process in such a manner that no appreciable amount of alcohol ever is formed in the ordillary free state in the nutrient.solution. On the contrary, this former process 55 has been so regulated that the alcohol compon(@nt s (carbon, hydrogen and oxygen) or some of them are seized upon as nutriment by the yeast cells at the instant of incipient alcohol formation and the alcohol tending to 60 form has bc@,-,n, in its incipiency or naseeiacy, so utilized by the yeast in @ome manner such as to avoid the actual accumulation of alcohol in the yeast-nutrient sglution. Contr ary to the hitherto pmvaling belief 65 above referred to, and unlike the process of Hayducl @ hereinbefore mentioned, my pr@sent inventioa is based upon the discov@ry that by proper conduct of a yeast-growing process, as hereinafter definitely described 70 in an exemplification of the said invention, a cousiderable accumulation or addition of al-cohol in aqueous solutions in w'hich yeast is,growin g,, may be utilized as food material by the yeast with a corresponding increase 7,5 in the amount of yeast produce-, such increase being directly traceable to additional yeast growth induced by the alcohol utilization. As illustrative of one method of practic- 80 ing my present invention, given by way of example only and without limiting myself to the details of such exaniple, yeast may be - produce d as follows: A "straight grain" mash is prepa;red from 85 cereal materials which. may comprige 35% corn, 40yo malt and 257o malt sprouts and this mash is "soured." The "souring" of the mash may be effected in accord with th@ method described i tho United States Pat- go ent to Alfred Polllalk, No. 1,123,920, by fernientatio n with lactic acid bactetia an'd neutraliz ation of lactic.acid thiis@ flormed iiu the mash by addition of ammonia or an ammonia derivative of suitable cliaracter. A suitable riiash is obtained. by carrying the souring to such an extent that a total of one liter of an aquegus solution c6nta,ining 267o of ammonia (NH,,) is utilized for eveil biishel of cereal material from wliieh the loo rnash was orilrinallv derived. essential was the conduct of the yeast-gtow- ' The rnash, prepared as described or in 2 1,722,858 other suitable and convenient manner, is filtered and diluted with water to tlio proper extent for use. as a yeast-nutrient mediiim in the aeration process, e. g,, 4 tli6 diltition may b(I such that %pproximaiel@ - 100 -allons of nutrieiit soliiti0h after dilution, are present for each bushel of total cereal materials employo-d in forming the mash as before described. 10 Stock yeast for seeding the Dutrient solution is added in the usual maliner to the extract of the mash, a suitable amount of yeast for this purpose bein- a quantity by. weight equal to about 2.57@ the weight of t-he total 15 nutrient substances present in the solutioii in which the, yeast is o-rown and, after adding the sto6li: yeast,'the solution containing the same is aerated as usual during the period allowed for yeast propagati6n whicli 20 may be about 16 hours or longer. . A small amount of sulfuric acid may be added to the batch, for example at about the termination of the fourteenth bour of the process, in case this is deemed advisable to compens,,ite 25 for the abseiiee of proper acidity for the completion of the process. Iri workino, with the particular nutrient solution juscdescribed, it will ordinarily -not be found iaecessary or useflil - to add 30 alkaline neutralizing alyents during the yeast growth but in workini with otber nutrients @ueb as . those containing large amouiits of inorganic ammonium salts and molasses it may be found advantageotis to. nebtralize 35 liberated inorganic acids prouressively during the yeast gi-owth by suitable additions of alkaline substances. Molasses and ammonia or ammonium salts may be used as yeast iiutrient mater@.als in connection with 40 my improved process, the principal modification made by my process being in the addition to the nutrient solution of a limited, quantity of alcohol such that the alcohol added is substantially utilized as a food ma,- 45 terial by the yeast durino, a subsequent period of the yea,st growth.- At a suitable time durino, the period of @? as propagation, for example, in a process above desci@ibed, at the end of the foiirth 50 hour there0f, there is added to the batch about 10@'o its volume of a 25 proof aqueous solution of alcohol and it has been discovcred by me, in the course of experiments, that by such addition the yield of yeast ob55 tained, (as compared with the yield of yeast produced by an absolutely similar process wherein a lil@e quantity of water is added at the same time instead of adding the alcohol solution) is increased by an 60 amount equal to about 67o (of the quant,ity of yeast obtained witbout the aleohol a(lditioia). The yeast obtained in increased amount by fne addition of alcohol as desciibed is of fully as (rood a quality for baking pur- (i5 poses as t@he To.wer yeast yield obtained withotit the addition of @ilcohol, proving that tho alcohol present is, in the conduct of iny improved process, desirable material in that it is actually utilized as a food mate- 7o rial and assimilated for the furtlier increase of the balcers' yeast itself. Instead of adding the a@cohol solution after the propagation has progressed for some time as a-bove referred to, it may be added'at the begin- 75 ning of the period of propagation (immediately before or after the introduction of the starting yeast i.nto the nutrient solution) and in such case a similar increase in yeast yield is obtained as in the case of addition 8c of the alcohol at a later stage in the, process. It has been found advisable, ordinarily to limit the quantity of alcohol present at any time in the yeast nutrient solution to a maximu'm of about 1.5@lo to 2@o alcohol by vol- 8@, ume in order to insure the complete utilization of the allcohol as a food material for biiildiii(- iip the substance of the yeast. It has been found desirable to provide an ample quantity of iiitrogenous substances, 9( utilizable by the yeast as a so-arce of nitro-ent for its -rowth, in order that the increased yield-of compressed yeast obtained by my process will have the uslial normal percentage c6ntent of nitrouen essential to 91 good baking or raising prope;ties in the yeast. The substance@ usually employed in 'yeast production, siieh for example as the cereal materials used in the production of the mash and nutrient wort hereinbefore described by 1( way of example, will ordinarily contain an ample supply of such nitrogenous substances. As above noted the addition of alcohol as described without any modification of the nitro-enous or other substances 1( present, either as respects the quantiiies or dilution of these substances results in the obtainment of materially increased yields of yeast. Having described my invention, what I I claim as new and desire to secure by Let-. ters Patent, is,@ 1. In the art of manufactur.ino, bakers' yeast, the improvement which c@omprises propagating yeast with aeration in a, yeast I nutrient sollition, and during the eriod of propagation adding ethyl alcohol to the propagatiiag liquid in such amounts as may be assimilited by the yeast without either materi,,.Hy inbib'iting the rate of propaga- I' tion or adversely affectin- the quality of the yeast whereby a substantial increase in the yield is obtained oi,er the yield obtainable from an otherwise substantially ideiitic,,Ll soliition without the addition of the ethyl I alcohol. 2. In tile art of manufacturing bakers' yeast, the improvement which comprises propagating yeast with aeration in a yeast nutrient solution@ and during -the period of propagation adding ethyl alochoi to the propagating Jiquid in an amount equivalent 5 to about 107'o of the volume of the propagating liquid, of 25 proof alcohol, wbereby a substantial increase in the yield of yeast is 3 obtained over the yield obtainable from an otherwise substantially identic'al solution without the addition of the ethyl alcohol, 10 without either substantially increasing the period of propagation or adversely affecting the qua.lity of the yeast. FRED RANSOHOFF.