May 2nd, 1SS7.] 



SCIENTIFIC NEWS. 



57 



cook might happen to make our coffee or our soup with 

 unfiltered Thames " entire," instead of with the pure water 

 conveyed, as some propose, from the head waters of the 

 Severn. 



Wherever the slightest doubt exists, water for drinking 

 and cooking should before use be passed through a spongy 

 iron filter, or one of unglazed porcelain on the Chamberland 

 principle. 



(To be continued.) 



FERMENTATION. 



IF we wished to illustrate the great distance which has 

 existed between the practical knowledge of the manu- 

 factures and the theoretical researches of the scientific man, 

 we could not find a more striking examp'e than the process 

 of fermentation — a process to which we owe our daily food 

 and our common drink, a process made use of from the 

 earliest times, and yet one the true nature of which it has 

 remained for the thinkers of the latter half of the present 

 century to reveal to us. 



We know that the Eg5'ptians made use of a strong drink 

 prepared from corn, similar in some respects to beer, about 

 2,000 years b.c. We read of the unleavened and leavened 

 bread of the Hebrews in the book of Exodus, and of strong 

 drink being forbidden to the priests in the book of Leviticus. 

 Among classical writers, Herodotus, jEschylus, Xenophon, 

 Pliny, and Tacitus mention fermented drinks in use in all then 

 civilised countries, and we know that the production of fer- 

 mented drinks has been carried on continuously to the present 

 day. Yet we owe to Pasteur our first accurate information re- 

 specting the ferments, their nature, habits, and varieties. 



Ferments have been many times classified into vinous, 

 acetous, putrefactive ; but these were believed to succeed 

 one another, as simple chemical changes, or to form the 

 links of a circular chain, one passing into another and 

 having to be arrested as alcohol or vinegar might be re- 

 quired. 



In a standard work on brewing, published about a century 

 ago, fermentation is defined as a " spontaneous separation 

 and removal from their former order of combination, and a 

 remarkable alteration in the subject by a new arrangement 

 and reunion."* The same dimness of ideas prevails even 

 in the scientific works of a later period, and we read in the 

 "Penny Cyclopaedia,"! published about 1830, that " Fer- 

 mentation denotes the spontaneous changes which occur in 

 certain vegetable and animal matters, and by which there 

 are produced new fluid and gaseous compounds." With 

 the use of the microscope came greater light, and in lire's 

 Dictionary, published in 1853, we read, " Yeast when viewed 

 in a good achromatic microscope consists of translucent, 

 spherical, and spheroidal particles, each about j^5'^y,^ inch in 

 diameter. The researches of Schulze, Cagniard de la Tours, 

 and Schwann appear to show that the vinous fermentation 

 and the putrefaction of animal matters — processes which 

 have hitherto been consideied as belonging entirely to the 

 domain of chemical affinity, are essentially the result of an 



organic development of living beings As the 



extract of nux vomica is known to be a poison to infusoria 

 (animalcules), but not to vegetating mould, while arsenic 

 is a poison to both, by these tests it was proved that the 

 living particles instrumental to fermentation belonged to the 

 order of plants of the confervoid family.' 



Notwithstanding this great step in the direction of truth, 



* Shannon, on "Brewing, Distilling, Wines, Cider, Spiiits, Vinegar," 

 p. 145. 

 t \'ol. X. Article, Fermentation, 



some of our great thinkers still fought for the chemical theory, 

 and to the close of his life one of the greatest chemists of 

 his age, Liebig, maintained the theory of chemical develop- 

 ment, even when Pasteur had already advanced far in those 

 experiments, the result of which has placed him amongst 

 the greatest of modern scientists. Although, seen by the 

 light of more recent researches, Liebig's theory is known to 

 be incorrect, the practices recommended by him are such as 

 to be most beneficial to the brewer and baker. He found 

 at what temperature alcoholic fermentation must take place 

 to render the products stable, not liable to further change. 

 He instructed the brewer to aerate the worts as much as 

 possible, as oxj'gen was necessary for healthy fermenta- 

 tion.* 



But Liebig further says : " When we examine strictly 

 the arguments by which this vital theory of fermentation is 

 supported and defended, we feel ourselves carried hack to 

 the infancy of science. ... It may be compared with the 

 idea of a child who explains the rapid fall and current c f 

 the Rhine through the numerous Rhine mills at Mayence, 

 by supposing that the mill wheels, by their force, urge the 

 water downwards towards Bingen."t 



But leaving past errors, Pasteur has proved that fermen- 

 tation cannot take place in the absence of organisms, 

 minute as they may be, yet not too m.inute to be examined 

 even with the present power of the microscope. These 

 organisms may be added to the saccharine solution pur- 

 posely and separately, as in the case of adding yeast to 

 malt wort, or together with the fruit itself, as in the case of 

 grape must, or cider, where the ferment is present on the 

 skin of the fruit, and is used unconsciously, thus giving rise 

 to the theory of spontaneous fermentation. The changes 

 which take place in beer, either before or after its comple- 

 tion, which give sour or other unpleasant flavours, are due 

 to separate organisms, introduced either with the yeast 

 itself or clinging to the utensils employed, or they may be 

 floating in the dust of the atmosphere. These disease 

 germs are smaller and more delicate than the yeast germs, 

 and conseciuently can be disposed of by antiseptics, which 

 only weaken the yeast. 



Neither of these ferments can in any case develop into 

 any other. 



True alcoholic ferments require oxygen for their vigoror.s 

 growth, and although yeast may exist without ox3'gen for a 

 longer time than some other ferments, it becomes weak and 

 impoverished without an abundant supply. 



Moreover Pasteur has confirmed Liebig's theory 01 

 fermenting at a low temperature, but we must agree rather 

 with Dr. Graham in taking exception to Pasteur's recommen- 

 dation of German beers for stability. The system on which 

 they are brewed makes them so susceptible to change of 

 temperature as to render their transport without ice 

 impossible. 



While acknowledging the great debt due to Pasteur for 

 his researches, we cannot agree with the revolution in 

 English manufacture of beer which he advises. The altera- 

 tion of method, and change of costly appliances, would be 

 a drawback, and there is no safeguard that the products 

 would be as saleable as what is manufactured under present 

 conditions. The so-called Pasteurization of beer m.ay also 

 practically be considered a failure. Although recommended 

 more than ten years since, it has never gained favour in 



* This led to the introduction of refrigerators on Bandelol's system. 

 When the first of these was introduced into an English brewery, a 

 number of large brewers met to consider its merits, and all but orie 

 condemned it without hesitation, "as a certain way of producing 

 vinegar." This identical machine is still in full work, altliough the 

 patent has long since died oat, and many imitations have followed it. 



t " Letters on Chemistry," p. 258. 



