THE COMBINED METHOD OF STERILISATION 93 



incapable of further development ; the wort is therefore practically sterile . 

 Sometimes but, as E. CH. HANSEN (HI.) has shown, not always the complete 

 destruction of all the germs (absolute sterility) is attained in this way. How- 

 ever, the residual living germs in the wort do not develop therein, though they 

 will do so if transferred to a more favourable medium e.g. meat-broth. In this 

 case we have to do with relative sterility. The rapidity of the effect is chiefly 

 attributable to the influence of the hops, which, in turn, owe their germicidal 

 powers to the possession of certain resinous bodies, generally known under the 

 collective name of hop-resins. The chemical properties and biological effects of 

 these bodies have been investigated by M. HAYDUCK (I.), who found three different 

 resins in hops, all of which are soluble in alcohol, ether, and chloroform. One of 

 these, viz., the brittle, tasteless y-resin, insoluble in petroleum spirit, does not 

 interest us in the present instance, the germicidal properties of the hop not 

 being due to its influence, but to that of the two (extremely bitter) soft resins 

 the a-resin and /3-resin. These two act powerfully on the lactic acid- and 

 butyric acid bacteria, but are innocuous towards acetic acid bacteria, sarcina, 

 and higher fungi (especially yeast). The latter organisms are, however, subject 

 to the influence of the boiling temperature, so that the wort is delivered in a 

 sterile condition to the cooler, where it is infected anew. The attempts of all 

 discerning brewing technicists to abolish the cooler and to effect the rapid cool- 

 ing of the wort (as well as its aeration by the injection of germ -free air) in 

 closed vessels fitted with refrigerating appliances, are thus easily accounted for. 

 This method of procedure, which, from the fermentation physiologist's point of 

 view, is the only correct one, is, however, beset with a difficulty as regards the 

 separation of the sedimentary matter. Therefore the hot wort from the copper is 

 generally allowed to stand until the sediment has subsided, the still hot goods being 

 then carefully drawn off and conveyed to suitable cooling and aerating apparatus. 

 For a description of the latter, reference must be made to Handbooks on Brew- 

 ing, three of which are recommended : that of THAUSING (I.) studies the wants 

 of the practical brewer; whilst MORITZ and MORRIS'S (I.) work is intended for 

 the brewing chemist familiar with chemistry and microbiology, to whom it 

 presents a large amount of lucid information. These two books being supple- 

 mentary one to the other, the student will do well to leave neither unread. 

 Finally, the third work, C. J. LINTNER'S (I.) "Handbuch der landwirtschaft- 

 lichen Gewerbe," is adapted for imparting instruction in High Schools. 



The sterilisation of wort in Pasteur flasks the medium most frequently 

 employed in the fermentation physiologist's laboratory will be briefly described 

 as an addendum to the preceding remarks. In order to produce a clear liquid, poor 

 in precipitated albuminoids, &c., the Pasteur flask is half filled with wort (not from 

 the hop copper, but from the cooler), which will now contain numerous germs, 

 several hundreds to thousands per c.c. The flask is then placed on a heated sand- 

 bath and the steam evolved is allowed to escape for ten minutes counting from the 

 moment boiling begins through the short caoutchouc tube on the lateral tube 

 of the flask, whereupon the former is closed by a glass stopper previously purified 

 in the flame. Then, for a further ten minutes, the steam is allowed to escape 

 through the swan-neck, and the flask is left to cool, being for that purpose placed 

 on a hollowed cork or a ring of millboard one inch in height. When the liquid has 

 again sunk to the temperature of the room, the moisture condensed in the swan- 

 neck is driven off by means of the gas-flame, and the neck is closed by a small plug 

 of asbestos, which subsequently serves as a germ filter. Any organisms capable of 

 passing through this are deposited in the first bend of the tube, which is then 

 freed therefrom, by heating it to redness in the flame, before proceeding to inocu- 

 lation. Concerning the sterilisation of the large copper apparatus for pure yeast 

 culture, detailed instructions have been given by E. CH. HANSEN (III.). 



