HVG Germany: Hopfen

 

hbrauerei_microbiol_1Due to their bacteriostatic effect hops have prevailed in brewing beer contrary to all the other spices. When there were no other means of refrigerating the master brewers knew from experience that the beer would keep longer if given a generous dosage of hops. It was Louis Pasteur who first discovered the influence of micro-organisms in fermentation and who in 1876 provided the proof in his "Études sur la Bière" that it was not "beer witches" but microscopically small organisms which make the beer sour.

hbrauerei_microbiol_2The alcohol and carbon-dioxide content, the low pH and the high final attenuation In the beer have a negative effect on the growth of micro-organisms. Pathogenic bacteria such as salmonella and staphylococcus cannot survive. For this reason beer was always regarded as a pure drink.
Nevertheless there are representatives of gram positive and gram negative bacteria as well as some wild yeasts which survive even under these conditions and which can cause turbidity and changes in the taste of the beer. Lactobacillus and pediococcus (gram +) and pectinatus and megasphaera (gram -) are among the master brewer's worst enemies.

Meanwhile numerous research papers exist on this subject. The intake of the isohumulones through the cell membrane of the micro-organisms and the resulting effects have been investigated in great detail. Thus lactobacillus in time develops a tolerance towards the bitter substances and this is passed on during the cell propagation.

hbrauerei_microbiol_3The different naturally and chemically modified hop products demonstrate varying inhibitive strength towards the beer-spoiling organisms. The alpha-acids possess the most inhibitive strength, the iso-alpha acids the least. For more details refer to the resulting publication (Investigations on the influence of hop products on the micro-biological stability of beer): 
Untersuchungen zum Einfluss von Hopfen-Produkten auf die mikrobiologische Stabilität des Bieres (.pdf , 1,6 MB)

hbrauerei_microbiol_5If the hop dosage is split up into several doses during the brewing process, also isomerized alpha-acids do not enter the beer. Consequently this process makes the beer even less sensitive towards the growth of micro-organisms. What the brewer knew hundreds of years ago through experience was confirmed by the scientists later on by researching the causes for the phenomena.