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I I
Alcoholic Fermentation of Acid-Hydrolyzed Grain Mashes J
J
CONTINUOUS PROCESS E. W. RUF, TT. H. STARK. L. A . SAIITH,
clrolyzed. I t w a s necessary to supplement acid-ti? tlrol? l e d mash with either wheat bran, mold bran, \I: lase, I < l I o s me ~
S, o r subnicrgetl niold culture to obtain jields equitalent to those obtained h? present commercial methods which ernploj barley malt coniersion of mash. Plant efficiencies of 8 i 7 ~ were obtained on t h e basis of the issociation of OKicial ;igricultural Chemists starch anal! sis of grain. The process is economicall? sound, requires a n ~ i n i m u nof~ equipment, and has considerable flexibility; i t lends itself well to commercial application.
havi, been modernized so thai processing subjcct to iniproved control i. the acc.eptcid method. There have becn many riiethods advanced, and sonic liavc been patentfd, for continuous fermentation. H o ~ v i.vixi', they have been iml)i,:ictical f r o m c i t h e r a n q u i p m e n t or an operational -~aii(lpoiiit. Some r e q u i r e ieriiientation time as long or Lingcar ihnn the conventional 1iiitt.h process, and t o date IiOlle has been commercially :iccc.pted. Tn.o principal p r o b 1e ins undcrlie tlie application of cnritinuous f ernie n t a t i o n . The first is bacterial contsmiiktion due to the malt, 1 the second, exceedingly sli,\v convcr~ioiiof the limit 1 Ic\;tyiiis. .lpproximatc~ly 707c of t h e a v a i l a b l e *t:ii,ch in grain is converted to fermentable sugar in It-* than 10 minutes. The I i~niaining 30y0 (primarily
liesearch oil the developnient of R i':tit, continuous fermentation process was liegun in the Seagram 1ahoratorie.sin 1910. I>?- investigating the
follovxd by continuous €ermentation studies on es; these studies were successfully completed early in 1942 arid have been pulilished ( 2 ) . Preliminary attempts to ferment continuously grain mash which had been converted with h r k y malt n-ere nnsurcessful. I t tention ~ ~ i i . thcn 7 directed to the continuous fernicntation of graiii mash t h a t n-as liytlrolyzed x i t h sulfuric aciil by the continuous process tlcscrihed by riigcr
1 Present address, Destileria +irrnlles, Inc., hlercedita, P u e r t o
1:1co
T7aiir Feeder and Sliirr) 'ratilc
1154
(4).
This pnper lpreeents t h e d e v el o p m e n t of this fcri i i c n t a t i o n process in the lnboratory 2nd s u b q u e n t pilot plant opcr nt 'ions conducted to obtain plant design data and an evaluation of the process on a commercial scale.
c r
INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
June 1948
1155
LABORATORY lIASH PREPARATION
Two thousand eight, hundred grams of ground corn were added to 7 liters of 0.17 A\- sulfuric acid contained in a &gallon carboy. This slurry was cooked in a laboratory pressure cooker for 4 niinutes a t 60 pounds steam pressure and then for 4 minutes a t 80 pounds pressure. .igitation and rapid heating were obtained in the slurry by introducing steam directly into the bottom of the carboy. The p H was adjusted to 4.8 to 5.0 rvith a n autoclaved calcium carbonate slurry, and the mash concentration \vas adjusted t o 38 gallons of mash per bushel with sterile xvater. The normal reducing sugar content (as glucose) of this mash was 12.5 to 12.6 grams per 100 nil. COKTINUOUS FERMEXTATIOK PROCEDURE
Prior t o operation of the laboratory continuous fermcnter, several batch fermentations of acid-hydrol!-zed mash were run in order to determine the rate of sugar utilization and the alcohol yield. From certain of these data presented in Table I, it n-as apparent t h a t most of the sugar x a s fermented in 8 hours, although the masimum yield was obtainpd some time between 8 and 36 hours. Batch fermentations viere regularly used as controls for the continuous fermentations and for preliminary investigations of most of the variables which were tried.
TABLEI. FASTBATCHFERUESTITIOS O F ACID HYDROLYZED MASH ~IECIIASICALLT ;\GIT.ATED Hours
' ; i
Sugar, G.,'100 111.
pH
Cell Count, 101
Alcohol, % by Yol.
Top View of Converz? me Propagator
Yield, Proof Gal.,'Bu.
T h e fermcnter vessel used \vas %gallon carbo>-immersed in a constant temperature rvatcr bath. It was equipped with a mechanical stirrer and the necessary large diameter glass tubing for the addition and removal of mash. The continuous system was operated as follows: 16 liters of acid-hydrolyzed mash were inoculated with 1.6 liters of a 20-hour culture of Seagram's yeast S o . 1T. The fermenting mash was held a t a temperature of 30" C. and agitated continuously until the sugar concentration dropped t o 3.0 to 4.0 grams per 100 ml. .it this point the fermenter contents 17-erereduced t o a n operating volume of 12 liters and the regular IVithdraxals and additions of mash begun. There were no further additions of yeast. The rnt,e of addition and withdrawal of the fermenter contents was determined by the reducing sugar level of the fernienting mash. T h e optimum rate was found to be 12.5% of the total fprmenter contcnts per hour, or a complete cycle in 8 hours. This verified earlier fast batch fermentations where it n'as found t h a t most of the sugar was fermented in 8 hours. Hourly sugar a n a l ~ m sby the Lane-Eynon method ( I ) , cell counts, and p H tvere run on the fermented mash withdrax-n. Alcohol analyses m r e made on composites. Xn aliquot of each withdrail-a1 over a 4-hour period was placed in a flask that was mechanically shaken in a 30" C. n-ater bath. This 4-hour composite was shaken an additional 4 hours and then analyzed for alcohol by distilling an Rliquot, and determining the refractive index of the distillate. Table I1 shows that fermentation was essentially complet
