[Footnote: 'Zeitschrift fur Analyt. Chemie,' 1881.]
Hop flowers contain a great variety of different substances susceptible
of extraction with ether, alcohol, and water, and distinguishable from
one another by tests of a more or less complex character. The substances
are: Ethereal oil, chlorophyl, hop tannin, phlobaphen, a wax-like
substance, the sulphate, ammoniate, phosphate, citrate and malates of
potash, arabine, a crystallized white and an amorphous brown resin, and
a bitter principle. That the characteristic action of the hops is due to
such of these constituents only as are of an organic nature is easy to
understand; but up to the present we are in ignorance whether it is upon
the oil, the wax, the resin, the tannin, the phlobaphen, or the bitter
principle individually, or upon them all collectively, that the effect
of the hops in brewing depends.
It is the rule to judge the strength and goodness of hops by the amount
of farina--the so-called lupuline; and as this contains the major
portion of the active constituents of the hop, there is no doubt that
approximately the amount of lupuline is a useful quantitative test. But
here we are confronted by the question whether the lupuline is to be
regarded as containing _all_ that is of any value in the hops and the
leaves, the organic principles in which pass undetected under such a
test, as supererogatory for brewers' purposes? Practical experience
negatives any such conclusion. Consequently, we are justified in
assuming that the concurrent development and the presence of the several
organic principles--the oil, the wax, the bitter, the tannin, the
phlobaphen, in the choicer sorts--are subject, within certain limits, to
variations depending on skilled culture and careful drying, and that the
aggregate of these principles has a certain attainable maximum in
the finer sorts, under the most favorable conditions of culture, and
another, lower maximum in less perfectly cultivated and wild sorts. The
difference in the proportion of active organic substance in each sort
must be determined by analysis. There then remains to be discovered
which of the aforesaid substances plays the leading role in brewing, and
also whether the presence of chlorophyl and inorganic salts in the hop
extract influences or alters the results.
That in brewing hops cannot be replaced by lupuline alone, even when the
latter is employed in relatively large quantities is well known, as also
that a considerable portion of the bitter principle of the hop is found
in the floral leaves. Neither can the lupuline be regarded as the only
active beer agent, as both the hop-tannin and the hop-resin serve to
precipitate the albuminous matter, and clarify and preserve the beer.
Both chemists and brewers would gladly welcome some method of testing
hops, which should be expeditious, and afford reliable results in
practical hands. To accomplish this account must be taken of all the
active organic constituents of the hops, which can be extracted either
with ether, alcohol, or water containing soda (for the conversion of the
hop tannin in phlobaphen).[1] It should further be ascertained whether
the chlorophyl percentage in the hop bells, new and old, is or is not
the same in cultivated and in wild hops, and whether the aggregate
percentages of organic and constituent observe the same limits.
[Footnote 1: See C. Etti, in "Dingler's Polytech. Journ.," 1878, p.
354.]
As wild hops nowadays are frequently introduced in brewing, the
proportion of chlorophyl and organic and inorganic constituents in them
should be compared with those of cultivated sorts, taking the best
Bavarian or Bohemian hops as the standard of measurement. The chlorophyl
is of minor importance, as it has little effect on the general results.
By a series of comparative analysis of cultivated and wild hops, in
which I would lay especial stress on parity of conditions in regard
of age and vegetation, the extreme limits of variation of which their
active organic principles are susceptible could be determined.
There is every reason to suppose that the chlorophyl and inorganic
constituents do not differ materially in the most widely different sorts
of hops. The more important differences lie in the proportions of hop
resin and tannin. When this is decided, the proportion of tannin or
phlobaphen in the hop extract or the beer can be determined by analysis
in the ordinary way. But whenever some quick and sure hop test shall
have been found, _appearance and aroma_ will still be most important
factors in any estimate of the value of hops. Here a question arises as
to whether hops from a warm or even a steppe climate, like that of
South Russia, contain the same proportion of ethereal oil--that is, of
aroma--as those from a cooler climate, like Bavaria and Bohemia, or
like certain other fruit species of southern growth, they are early
in maturing, prolific, large in size, and abounding in farina, but
_deficient in aroma_.
The bearings of certain experimental data on this point I reserve for
consideration upon a future occasion.--_The Analyst_.
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