INDUSTRIAL FERMENTATIONS 315 



One uf the chief ooutaiiiinants pr(j(hi('iii<z unsalisfactoiy 

 fermentatioji is a lactic acid organism which can bring 

 the butyl alcohol fermentation to a complete standstill in 

 a few hours. A bacteriophage has also been incriminated 

 as the cause of faulty fermentations. The early method 

 of sterilisation of the mash in large tanks prior to fer- 

 mentation had to be abandoned in favour of the use of a 

 number of small tanks in order to ensure thorough penetra- 

 tion of the heat. The grain, usually maize, to be fermented 

 is freed from the embryo (from which an edible oil is 

 expressed, leaving a cake used as cattle food), sterilised as 

 a mash in water by steam under pressure at 130° to 140° C, 

 and transferred through sterile pipe lines to a large fer- 

 menting tank holding as much as 50,000 gallons. A seed 

 mash, built up from j)ure laboratory cultures, or withdrawn 

 from a previous fermentation, is introduced and fermenta- 

 tion allowed to proceed at 55° C. The production of a 

 maximum yield of products in the minimum of time 

 depends largely on the preparation of the seed mash. 

 This must bear the correct ratio to the total mash to be 

 fermented (usually about 12 per cent.), and the number 

 of subcultures used to ])uild the seed up to the requisite 

 amount is kept as low as possible in order to maintain the 

 activity of the organism. The seed is withdrawn after 

 the initial acidity of the fermentation has begun to decline, 

 since the main contaminant to be expected is the lactic 

 acid organism, B. volutans, whose presence is indicated 

 by the maintenance of a high acidity ; hence a sample 

 taken from a mash whose acidity is declining is more 

 likely to be pure. 



Anaerobic conditions develop automatically ; the 

 fermentation starts in five to six hours and is complete 

 in forty-eight hours. In addition to butyl alcohol and 

 acetone, carbon dioxide, hydrogen and ethyl alcohol are 

 also formed, together with small amounts of z5o-propyl 

 alcohol. The chief products occur in the proportions : — 



