Editor’s note – This paper appeared in Hantke’s “Letters on Brewing”; a trade journal in 1906. The text, while interesting, simply reinforces the statement made in the first paragraph. With the advent of whirlpool hopping and the dry hopping of most styles of beer these days, it is certainly worth thinking about.
The Microorganisms of Hops
By A. Fischer and Dr. M. Kuensberg
The microorganisms of hops cannot injure the lager beer, as they are destroyed during the boiling; but they may cause injury in the production of ale where the hops are put directly into the cask. The peculiar taste of several ales leads us to investigate this matter.
In our experimentation we used different varieties of New York, California, Saaz and Spalt hops of the 1904 and 1905 harvest. The hops were taken from bales before taking samples, with sterile instruments and put into bottles which were previously heated to 150 ° C. for 2 hours.
To examine the microorganisms adhering to the strobiles, three strobiles were taken from the sterile container and put into small flasks containing 200 cc. sterile water for 6 hours and shaken at intervals. After this time plate-cultures of wort-agar, hop-agar and meat-gelatine were made using 1/100 cc. from each of the flasks. These plates were then placed in a cool place for development.
The hop-agar was prepared by steeping 20 grams of imported hops in one and one-half liters of water for 12 hours and then boiling for 1 hour. After cooling the hops were pressed and the liquid filtered. The clear filtrate was of a dark color. One per cent of agar was then added to it and the mixture filtered, where upon it was immediately sterilized.
Although the hops came from various regions the yield of microorganisms was not as large as expected. There developed a number of colonies on the different culture media as given below.
The cultures contained yeasts, mold fungi and bacteria, the short rod bacilli predominating of the latter; sarcina could not be determined. The isolated mold fungi colonies included the brush mold (Penicillium glaucum), the Domatium pullulans, Aspergillus glaucus, a chocolate-colored mold fungus which appeared to be similar to the one described in Lindner “Mikroskopische Betriebs-kontrolle in den Gärungsgewerben.” This fungus was isolated from the 1904 Spalt hops. When sown on wort-gelatine it showed a number of small spherical colonies which appeared to consist of chains of spores. The chains are close together and consist of oval spores. Sterigma could not be detected.
There was another fungus which we have not yet identified. The fungus forms a velvet-like mycelium which appears pink or better flesh-colored after a time. The hyphae often form thick interlaced threads, having a marked branching and form at their ends a thick, spherical fruit of oval spores. Occasionally these fruit bodies are observed in the center of the branched hyphae. This fungus was also isolated from the Spalt hops of 1904 and 1905.
The bacteria which were separated from 7 hop samples comprised 7 varieties as follows:
New York 1905.
1. Very motile bacilli, liquifying gelatine very rapidly. The streak culture is funnel-shaped and rapidly liquified. On gelatine there is formed a delicate, mother-of-pearl-like, glossy membrane.
2. Small fine non-motile rods of diplococci order which do not liquify gelatine. The streak culture resembles a chain of pearls, spreading over the entire gelatine and appearing greyish – white, smooth and dull – glossy at the surface.
California 1904. White, glossy, strongly strangulated colony, which slowly liquifies gelatine beginning from above. The streak culture spreads flatly into the streak, but ragged at the margin.
California 1905. The yellow colony is composed of small short nonmotile rods. It is non-liquifying. The streak culture grows flat and ragged into the streak.
Saaz 1905. The colony is of a yellowish-brown color. After a time, the rods form long threads having endogenous spores. The gelatine is slowly liquified and assumes a darker yellow color passing slowly into green. The streak culture is slowly liquified from above.
Spalt 1904. Colony whitish, glossy, slimy, small rods. They are strangulated, motile and non-liquifying. The streak culture resembles a string of pearls.
Spalt 1905. The dark red glossy colony consists of micrococci. Molecular motion. They do not liquify gelatine. The streak culture is smooth and of a reddish color in the streak.
Oregon 1905.
1. The colony is white, becoming dirty brown at the margin. Consists of large staphylococci in marked irregular lumps. The streak culture forms lumps in the streak. The colony is non-liquifying.
2. The colony is composed of small motile rods which do not liquify gelatine. The colony is colored yellow. It forms a smooth streak culture colored yellow in the streak.
All the above-mentioned bacteria were inoculated into finished bottled beer and the bottles placed into a thermostat for 14 days, whereupon they were examined microscopically. In nearly all bottles an increase of bacteria was notice- able although most of the bacteria were destroyed in the course of time. The only bottle which showed a slight increase was that inoculated with the staphylococci isolated from the Oregon hops of 1905, but here also the staphylococci were greatly retarded in their development. No harmful influence was observed in any instance.
Besides the mold fungi and bacteria nearly all colonies showed the presence of torula yeasts, both white and red. Among the white colonies a perfectly spherical yeast may be mentioned which had a diameter of 5-7.5 µ. It was isolated from the New York hops.
Two colonies isolated from the Spalt hops of 1905 were found to be of the same species.
The yeast is of a long oval shape and has a diameter of 5 to 8 µ.
The bacteria described above were studied more in detail; the results follow below.
Two colonies were isolated from the New York 1905 hops.
1. This is a small motile rod 1.8 to 2.0 μ long and 1 wide. On gelatine plate there developed at first a white, round, sharp margined colony which became larger after a short time and liquified gelatine, producing a greenish fluorescence. The streak culture developed rapidly and luxuriantly on agar forming a greenish-yellow colony. On potato it forms a thin, grey, delicate membrane. The streak culture quickly liquified gelatine in a funnel-shape manner. The bacterium does not stain according to the Gram method.
2. This consists of small, delicate, non-motile rods, of diplococci form. 3.7-5 μ long and 0.5 µ in width. On gelatine plate sharp rounded, dull, grayish white colonies are produced. They are non-liquifying. There is a luxuriant growth on agar appearing as a greyish-white membrane. On potato a poorly developed dull grey skin is formed. The gelatine streak culture resembles a string of pearls of spherical drop-like form. Gram’s staining results negatively.
California 1904. The rods are 1.5 to 2 μ long and 0.6 wide. They are non-motile, strangulated and liquify gelatine. The colony is glossy white and sharply margined.
10 cc. gelatine contained in a tube was half liquid after about three months. On agar there was formed a thin, smooth, white membrane which passed into a brownish tint. The development was hardly noticeable on potato. It appeared as a fine colorless skin. The gelatine streak culture spread flatly into the streak, it having a ragged margin. The gelatine was slowly liquified from above. The rods were not stained by Gram’s method.
California 1905. The non-motile rods were 4.5-6 µ long and 0.5 μ in width. On gelatine and on agar sharp bounded smooth colonies of lemon-yellow color developed. On potato the development was slow and slight, being colorless at first and turning yellow after several days. The culture media is not colored. The streak culture is ragged in the cut surface.
Saaz 1905. The bacilli are 0.8-1.2 μ long and 0.4 wide. They form threads with endogenous spores after a time. Gelatine is liquified and shows a dark yellow to dark brown coloration which becomes greenish after a time. The colony on the gelatine plate is drop-like and of yellow-brown color. On agar there is produced a yellow viscous growth which turns brown. The streak culture liquified slowly at first in a funnel-like manner from the surface, later uniformly going to the bottom. The liquified gelatine takes on a disagreeable rotten odor. On potato a luxuriant dirty yellow growth develops. The staining with Gram’s stain gave negative results.
Spalt 1904. The rods are strangulated, 0.7 μ long and 0.5 μ in width. They are motile and have cilia at the periphery. On gelatine plate a white, glossy, drop-like colony developed having a viscous consistency. Luxuriant greyish-white growth appeared on agar. On potato a thin scarcely perceptible membrane was formed. The streak culture showed a string of pearl-like growth.
Spalt 1905. Cocci 0.6 to 1 µ in diameter. The gelatine plate culture appeared rose-red at first and dark red later. They possess a quivering motion. On gelatine and on agar they developed with beautiful dark rose to red color without coloring the substratum. The culture grows on both media rapidly and luxuriantly, forming many small spheres. The potato showed slight development, the growth being of a dark red color. The streak culture is smooth and full in the streak.
Oregon 1905. Two colonies were isolated.
1. Staphylococci. The diameter of the single coccus was 1 to 1.2 μ. On gelatine there developed sharp margined, irregular, pointed colonies of a dirty, white color becoming brownish in the middle. The colony is smooth and moist. Gelatine is not liquified. On agar a luxuriant growth developed, while on potato a thin yellow membrane was formed. The staphylococci gave a positive coloration with Gram’s stain.
2. The second colony were very motile bacilli, 0.7 μ long and 0.5 µ in width, with lophotricha cilia. On gelatine small dirty yellow colonies developed with a sharp margined smooth surface. There was a marked development on agar similar to that on gelatine. On potato a strong, folded, yellow growth developed. Gelatine was not liquified. No coloration was produced according to Gram.
There were fermentation tests made with the torula yeasts isolated from the hops. None of the spherical yeasts were able to ferment maltose, cane sugar or dextrose. The yeasts multiplied but slightly in cane sugar and dextrose sugar solutions. The reproduction in maltose sugar solution was more pronounced, the sediment being of a slimy nature.
The large spherical yeast with a diameter of 5 – 7.5 μ appeared to be identical with the torula yeast No. 63 described by Lindner. The cells are round and very large and have a homogenous plasma.
The first experiments with the yeast isolated from Spalt hops were repeated and again verified. The experiments with this yeast are not yet completed and the results will be incorporated in a later paper.
Crescent City Brew Talk 