230 CONTROL OF ROPE IN BREAD 



rope depends upon the existence of a hydrogen ion concentration in 

 bread sensibly less than about 10~^N, secondly, that such a condition 

 is likely to exist in war bread or other loaves which contain something 

 besides white wheat flour, and thirdly, that the action of acid as a pre- 

 ventive of rope depends primarily upon the increase of the hydrogen 

 ion concentration. 



These investigations clearly show that the growth of Bacillus mes- 

 entericus is a function of the hydrogen ion concentration of the me- 

 dium and that it is favored by the diminished hydrogen ion concentra- 

 tion which is due to the products of its own metabolism. This change 

 in the hydrogen ion concentration may serve as a measure of the 

 growth of the organism and as a means of identification. 



It is also interesting to observe that the growth of yeast tends to 

 produce a very acid reaction, — perhaps pH 4.5. Such a reaction 

 effectively checks the development of Bacillus mesentericus as well 

 as of most other organisms. Unquestionably this peculiarity of the 

 metabolism of yeast has much to do with the ease with which pure 

 cultures of yeast are obtained, preserved, and employed in baking 

 and brewing. For example, the 12 hour sponge process of bread mak- 

 ing may sometimes effectively safeguard the bread. It must not be 

 supposed, however, that an acid culture of yeast is necessarily free 

 from spores. 



As a result of this investigation it Seems clear that, when pos- 

 sible, the hydrogen ion concentration of bread should be maintained 

 near 10~^N. Our observations upon ropy bread, both in the lab- 

 oratory and in the bakery, seem to indicate that such practice would 

 prevent the occurrence of rope. The reaction of dough and bread may 

 be controlled with the help of a suitable indicator, and perhaps more 

 conveniently by the use of a buffer mixture consisting of lactic acid 

 and a lactate or acetic acid and an acetate. 



At present the simplest method of controlling the reaction of 

 dough or bread consists in the use of methyl red. When this indi- 

 cator is colored red rather than orange, we believe the reaction to be 

 sufficiently acid to prevent the development of rope. 



