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CHAPTER IV. 

 MOULDS. 



CERTAIN moulds as well as bacteria are of industrial import- 

 ance, and have been applied in the form of properly selected 

 pure cultures. On the other hand, a large number of species 

 are known that produce objectionable diseases in the different 

 branches of the fermentation industry. They select as their 

 habitat the vessels, tools, rooms, the green malt, and the 

 quiescent masses of yeast, especially top-fermentation yeast. 

 As shown below, the moulds usually play a subordinate, but 

 nevertheless a quite important part. A close examination 

 of mould growths taken from the ceiling or walls of a fermenting 

 room, or from the edge of a vessel, soon shows that they 

 scarcely ever consist of an unmixed growth of moulds. 

 Amongst the mycelia, bacteria and yeast-like cells can almost 

 always be found. The hyphae of the mould plant project 

 outwards, carrying foreign germs with them, and these, in 

 their exposed situation, are easily swept away either by air 

 currents or by workmen. All kinds of micro-organisms occur 

 on the raw material during the malting process. If moulds 

 are usually considered to be the worst enemies, it is due to 

 the fact that they are visible to the naked eye, and so attract 

 special attention. If we judge by numbers, then bacteria 

 must certainly take the first place, for they are always present 

 in great numbers on green malt. It may even be considered 

 doubtful whether the greatest influence on the product must 

 be attributed to the moulds (Penicillium, Aspergillus, etc.), 

 when these are met with in a state of vigorous development 

 on malt, or whether it is not far more probable that the 

 numerous organisms accompanying them play the most 

 important part. It is doubtful whether the so-called 

 " mouldy " smell of beer is caused by moulds. Observations 



