Table Of ContentDevelopments in Crop Science
Volume 1 Oil Palm Research, edited by R.H.V. Corley, J. J. Hardon and B. J. Wood
Volume 2 Application of Mutation Breeding Methods in the Improvement of Vegetatively
Propagated Crops, by C. Broertjes and A. M. van Harten
Volume 3 Wheat Studies, by H. Kihara
Volume 4 The Biology and Control of Weeds in Sugarcane, by S. Y. Peng
Volume 5 Plant Tissue Culture: Theory and Practice, by S. S. Bhojwani and M. K. Razdan
Volume 6 Trace Elements in Plants, by M. Ya. Shkolnik
Volume 7 Biology of Rice, edited by S. Tsunoda and N. Takahashi
Volume 8 Processes and Control of Plant Senescence, edited by Y. Y. Leshem, A. H. Halevy
and Ch. Frenkel
Volume 9 Taigu Male Sterile Wheat, by Deng Yang Zheng
Volume 10 Cultivating Edible Fungi, edited by P. J. Wuest, D. J. Royse and R. B. Beelman
Volume 11 Sugar Improvement through Breeding, edited by D. J. Heinz
Volume 12 Applied Mutation Breeding for Vegetatively Propagated Crops, by C. Broertjes
and A.M. van Harten
Volume 13 Yield Formation in the Main Field Crops, by J. Petr, V. Cerny and L. Hrusica
Volume 14 Origin of Cultivated Rice, by H. Oka
Volume 15 Nutritional Disorders of Cultivated Plants, edited by W. Bergmann
Volume 16 Hop Production, edited by V. RyM£ek
Developments in Crop Science 16
Hop Production
Edited by
Vaclav RybaCek
Faculty of Agronomy, Agricultural University, Prague, Czechoslovakia
ELSEVIER
Amsterdam - Oxford - New York - Tokyo 1991
List of authors:
Prof. Ing. VSclav Fric, Ph.D., Prof. Ing. Josef Havel, Ph.D., Ing. Vladimir Libich, Ph.D., Ing. Josef KffZ,
Ph.D., Ing. Karel Makovec, Ph.D., Ing. ZdenSk Pertlik, Ph.D., Prof. Ing. Vaclav Rytacek, Ph.D., Ing.
Jaromir Sachl, Ph.D., Ing. Antonin Srp, Ph.D., Ing. Josef Snobl, Ph.D., Ing. Miroslav Van£ura
Editor:
Prof. Ing. Vdclav Ryb^ek, Ph.D.
Scientific editors:
Prof. Ing. dr. Ladislav HruSka, Ph.D., prof. MikuldS Klapal
Drawings:
Otakar Prochdzka
Revised translation of the Czech edition Chmelafstvi published by the State Agricultural Publishing
House - Prague. Czechoslovakia
Distribution of this book is being handled by the following publishers:
For the United States and Canada
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Elsevier Science Publishers
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Library of Congress Cataloging in Publication Data
Chmelafstvi. English
Hop production/edited by V. Ryba£ek.
p. cm. - (Developments in crop science; 16)
Includes bibliographical references.
ISBN 0-444-98770-3
1. Hops. 2. Hops-Harvesting. 3. Hops-Economic aspects.
I. Rybadek, V. (Vaclav) II. Title. III. Series.
SB317.H64C4713 1990
633.8'2-dc20 89-26275 CIP
ISBN 0-444-98770-3 (Vol.16)
ISBN 0-444-41617-X (Series)
Joint edition published by
Elsevier Science Publishers, Amsterdam, The Netherlands and SZN, State Agricultural Publishing
House, Prague, Czechoslovakia
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or
transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise,
without the prior written permission of the copyright owner.
Copyright © 1991 by St£tni zemSdglske nakladatelstvi, Praha
Translated by Jaromir A. MaSa, Ph.D.,
Printed in Czechoslovakia.
INTRODUCTION
The utilization of new knowledge in natural and social sciences is important not only for the
scientific and technical progress of hop production but also for that of other crops. Crop
production reflects the biological, technical and economic aspects of production technology,
and it must also respect, and apply, new scientific knowledge. Conversely, when new urgent
problems arise in production technology they should be immediately included in the
programmes of scientific and technical research.
In hops, new knowledge results from scientific research, from scientifically verified field
experiments, and from accurate observations in hop production. This knowledge represents
the starting point of the common procedure: research - production - application. The short-
term and long-term trends in other fields of research into plant production should be
considered not only in relation to current and forecast trends in hop production but also to
future hop research.
Hop cones constitute the main harvest product, and because their quality and their
applicability to the brewing process are the main concern of hop production, the chapter on
the application of hop products precedes the chapters on hop production.
In order to make particular aspects of production technology more easily understood, there
are separate chapters entitled "Biological bases of production" and "Organization and
economics of production". Technical operations, especially those involving mechanization
and the application of chemicals are concerned directly in the technology of hop production,
a term which also includes the various biological and economical components. These basic
components of production technology must be considered in their complex interrelationships
involving the whole production process and in their non-interchangeability, i.e. the state of
their equivalency.
Clearly the fundamental basis of production technology resides in the biological properties
of the hop plant. This does not mean, however, that the whole production technology is totally
governed by the biological requirements of the hop plant. On the contrary, the technical and
economic aspects of hop production require certain deviations from the optimal require-
ments. The ability to make these deviations in favour of large scale production technology is
limited by the potential adaptability of the hop. Where the tolerable adaptability is exceeded
and the basic biological requirements of the plant are not satisfied, then the whole basis of
production is threatened, because this depends almost entirely on the production capacity of
hop vegetation.
Any non-adherence to the technical and economical aspects of production is clearly
reflected in the efficiency of production. Thus a continuous inefficiency endangers productivi-
ty in direct relation to the production capacity of the crop. The maximum harmony of those
biological, technical and economic aspects characteristic of the whole production process will
achieve the maximum yield from the planned hop production.
11
CHAPTER I
CULTIVATION AND UTILIZATION OF HOP PRODUCTS
The hop cone is, without doubt, the most important raw material for beer production due to
the bitter taste which it imports. Moreover, since the bitterness of the beer is a dominant factor
in its acceptability it follows that the hop is decisive in the final taste of beer. The hop cone has
many components, but not all of them are involved in beer technology nor in the final product.
MAIN COMPONENTS OF HOP CONES
Lupulinic resins
From the standpoint of brewing, the most important substances in the cones of hop are
lupulinic resins, as they are the cause of the bitter taste. These resins are a mixture of sparingly
soluble substances. Shown below is a basic classification of lupulinic resins followed by
a description of their features in an attempt to clarify a complicated situation.
Classification of lupulinic resins:
1. soft resins: 1.1. a-bitter acids (humulones);
1.2. (3-bitter acids (lupulones);
1.3. y-bitter acids (humulinones);
1.4. 6-bitter acids (hulupones);
1.5. e-bitter acids (not yet specified);
2. hard resins: 2.1. 6-resins;
2.2. y-resins.
As shown in this classification, it is possible to divide the lupulinic resins into two main
fractions, and from the standpoint of brewing the most valuable is the group of soft resins.
The soft resins
The soft resins include many substances which contribute to different extents to the final
bitterness of the beer. The most important are the optically active a-bitter acids (humulones).
They are a mixture of five different homologues characterized by different radicals in the
second position of a benzene nucleus. Their oxidation produces y-bitter acids (humulinones)
with a pentacyclic structure and they similarly consist of five different homologues. They are
less bitter than the a-bitter acids. The ultimate oxidation products of a-bitter acids are the
6-resins which are included in the hard resins. Their bitterness ranges from 15 to 20 per cent of
that of the a-bitter acids.
The (3-bitter acids are in fact not bitter. Chemically they again consist of a mixture of five
homologues. Unlike the a-bitter acids they are not optically active.
12
The oxidation of (3-acids produces 6-acids (hulupones) with a pentacyclic structure. Unlike
their precursors, the p-bitter acids, these compounds are bitter and make an important
contribution (30 to 50 per cent) to the final bitterness of the beer. Their further oxidation
produces insoluble y-resins lowering the value of hop for brewing. This resin fraction too is
included in the group of hard resins.
There are different levels of bitterness among certain non specified soft resins. This fraction
includes transformation products of the original bitter acids with as yet unknown structures.
The hard resins
The hard resins had for long been assumed to be inactive ballast. Only later was it shown
that the members of one fraction of these resins, the so-called 6-resins, are very soluble and
are bitter.
Czech hops, as distinguished from those of foreign provenance are typically well-endowed
with a-bitter acids and the p-fraction (a complex of soft resins without the a-bitter acids) in the
proportion of 1:1.2 to 1:1.5 i.e. more of the p-fraction than the a-bitter acids.
The a-bitter acids make their impact when fresh hops are used and their effect as the bitter
substances in the beer decreases with increasing duration of storage. With regard to the
quality of bitterness, our investigations have shown that unlike the p-fraction, the a-
-bitter acids have a tendency to produce rough and pronounced bitterness in the beer. We
have verified, in numerous examinations, that the p-fraction is less efficient than the a-bitter
acids in terms of quantity of bitterness, but it produces a gentle bitterness. This leads to the
conclusion that hops with a higher content of p-fraction are better as a raw material for
production of beers with a fine harmonious bitterness. The soluble hard resins, the so-called 6-
resins, are also bitter. Their contribution to the total bitterness of the beer is, however, the
least and depends on the content of the resin fraction in the hops. This content increases with
the increasing length of the storage period. Qualitatively, the bitterness of the 6-resins is
regarded as rough and crude.
This short survey has indicated the importance and effectiveness of individual resin
fractions in imparting bitterness to beer. Quantitatively, the a-bitter acids are foremost,
followed by the p-fraction and finally the 6-fraction, but qualitatively the p-fraction leads the
a-bitter acids followed by the y-resins. The a-bitter acids are very sparingly soluble and only in
prolonged boiling are they transformed to very soluble and intensely bitter iso-a-acids. This
transformation is effected by many factors, particularly by the intensity of boiling and by the
pH. The original p-acids unlike the a-bitter acids are not transformed to their isomers by
boiling. The p-bitter acids are transformed by polymerization and oxidation to products which
are bitter and highly soluble in the fresh mash. These transformations proceed to a small
extent during maturation of hop and increasingly during storage and the boiling process. Non-
specified soft resins and 6-resins are soluble and are taken up by the fresh mash during the
boiling stage.
The various components of lupulinic resin affect the brewing qualities of the hop as
measured by its contribution of bitterness. Authorities differ in their evaluation of the
effectiveness of the various components and consequently there are many formulae for the use
of the hop in brewing. Mentioned below are some of the formulae used to determine the
amount of hops to be used in brewing.
The first formula was derived by WOLLMER (1925) as follows:
value of bitterness = a +(p/9),
where a = quantity of a-bitter acids in per cent;
p = quantity of the p-fraction in per cent.
13
In practice it was found, that this formula could be used only for fresh hops but is
unsatisfactory for hops whose content of hard resins exceeds 15 per cent. Therefore,
KOHLBACH (1939) proposed another formula to calculate the bitterness for older hops:
0(100 - OAb)
value of bitterness = _
1QQ 22b
where a = value of bitterness according to Wollmer;
b = content of hard resins in per cent minus 15.
This formula, however, did not find broad application. It is clear that both formulae,
especially Wollmer's assume, that the a-bitter acids account for the bitterness of beer, but
worldwide research has shown, that this is not correct. SALAC and DYR (1944) for example,
proved, that the bitterness of p-fraction is not 1/9 of the a-bitter acids as given in Wollmer's
formula (1925), but is 1/3. Therefore, the formula was modified by these authors (1944):
P
value of bitterness = oc + -
Similar conclusions were reached by TOMBEUR and DE CLERCK (1934) and MIK-
SCHIK (1963). New knowledge about the properties of the hard resins led to more suitable
formulae, for the expressions of hop bitterness. According to VANCURA and BEDNAR
(1963) this value can be objectively expressed according to the quantity of so called "effective
bitter substances", calculated as follows:
effective substances (%) = MP (%) + 6 (%),
where MP = quantity of soft resins in per cent;
6-resins are also in per cent.
For the purposes of this formula the quantity of y-resins can be determined by calculation
based on current values, according to Wollmer's analysis (WOLLMER, 1925). Dosing with
hops according to this formula was confirmed in operative conditions as being correct.
One of the most recent methods for the establishment of the hop bitterness is that of
PFENNINGER and SCHUR (1968). These authors give an expression for general bitterness
as the milligrams of bitter substances present in a solution made from 1 gram of hop. Under
laboratory conditions, a sample of hop is boiled for sixty minutes in buffer solution at pH 5.55.
Bitter substances are extracted from this solution by chloroform and their quantity established
by spectrophotometry. General bitterness is calculated according to the formula:
, £ 79 X 115
2
general bitterness (mg.g-1) = ^
where E279 = extinction of chloroform extract at wave length 279 nm;
n = mass of the sample in grams.
Unlike the previous method, this method involves better laboratory equipment (spectro-
photometer).
These formulae for the value of bitterness of hop indicate its importance for the production
of beer with standardized and reproducible bitterness. Because the bitterness of the same hop
changes during the storage and because different hops are distinguished by different values,
the objective analytical establishment of bitterness is increasingly important and its applicati-
on to the brewing industry grows. According to the investigation of the Brewing Research
Institute in Zurich (Switzerland) almost 50 per cent of the breweries questioned in 1973 used
hops at a rate calculated according to the analytically determined value of their bitterness.
14
Lupulinic tannin - polyphenol substances
Another component of hop, important in brewing, is the lupulinic tannin. This i sa mixture
of polyphenolic substances whose main components are anthocyanins and leucoanthocyanins,
flavonols and catechins. This mixture is soluble in water and reacts very actively with malt
proteins. Its effect on the production of beer (Czech type) is as follows:
1. It positively affects the strength and quality of the beer as well as the boiling process when
it has a clearing effect on medium-molecular proteins. At the same time it holds the high
molecular proteins in solution.
2. It promotes complex formation between proteins and bitter substances. There is thus
a verified stabilizing effect of lupulinic tannin on bitter substances.
3. It participates to a large extent in the formation of the flavour regarded as typical of Czech
beers.
There are, however, certain negative properties attributed to the lupulinic tannin. It has,
for example, an unfavourable effect on the colloid stability of the beer. It should be mentioned
here that STEINER (1965) suggested, that only 10-20 per cent of the total polyphenol
substances in beer originates from the hop. The colloidal stability o fthe beer is probably more
affected by other polyphenol substances derived mainly from malt.
Hop essential oil
Hop oil consists of a mixture of hydrocarbons and oxygenous complexes of terpene series.
This mixture is mostly composed of the hydrocarbon fraction (60-70 per cent) containing such
important essential oils as humulene, myrcene, farnesene and caryophyllene. The most
important oils in the oxygenous fraction are geraniol and terpineol. More than 200
components of the hop oil have now been isolated.
The least hop oil was found in fine hops (0.2-0.3 per cent), but in so-called crude hops there
may be up to four times as much. Hop oil is practically insoluble in water but it is high volatile
in water vapour. Therefore, it is not involved in the production of beer during the period when
fresh hops are processed. More than 90 per cent of the oil volatilizes during the boiling period
and the traces found in the hopped wort disappear during the primary and secondary
fermentation. Therefore, no hop essential oils can be found in the finished beer.
The essential oils are transformed by oxidation and, consequently, their chemical and
physical properties are changed. In particular their solubility increases and their volatility
decreases. Under certain conditions some of the products of this transformation can pass into
the finished beer and reduce its quality. Such an undesirable effect is likely when hops of
a particular age are processed.
It can thus be concluded that the hop essential oil is useful in commerce only when the group
to which a particular of hop belongs might be distinguished by scent.
Other constituents
In addition to resins, tannins and oils many other constituents are present in hop, such as
saccharides, nitrogen compounds, lipids, waxes, sulphur dioxide and heavy metals. These
components have no essential effect on the technology of production nor on the quality of the
beer. The heavy metals (Cu, Zn, Mn, Fe) are taken up by the hop plant mostly from the
chemicals used as crop protectant sprays. These are normally adsorbed onto the bitter dregs
during the hopped wort production. Sulphur dioxide is not present in the original hops but
arises from the treatment of the crop with sulphur. BRENNER and BERNSTEIN (1975)
15
stated that the frothing quality of beer, more particularly, the stability of the froth will be
adversely affected if the content of sulphur dioxide in the hopped wort exceeds 25 mg per litre.
A greater content of nitrogen compounds will unfavourably affect the activity of the yeast.
According to POSTL (1975) certain microorganisms are able to reduce nitrates to nitrites
which are toxic to yeasts. When very old hops are processed their lipids can spoil the flavour of
the beer. Nitrogen compounds consisting mainly of proteins and their decomposition product
do not themselves affect the quality of beer, but according to NARZISS and BELLMER
(1975), their reaction with saccharides produces substances which intensify the colour of beer.
Pectins increase the effect of bitter substances.
This section has included a brief description of the typical features of substances contained
in the hop as well as an indication of their effect on the technology and quality of beer. This
survey shows that the dominant components are the hop resins. These substances are,
however, unstable so that undesirable changes occur during storage and these changes
gradually reduce the value of the Hop for brewing. Even under good storage conditions the
brewing value of hop decreases by 10-15 per cent per year.
Under the classical brewing process there is a poor level of utilization of the bitter
substances from the hop. Thus, experience with production of Czech beers hopped with large
doses, approximately 85 per cent of the bitter substances pass into the wort, i.e. approximately
15 per cent of the hop resins remain in the hops. Taking the quantity of bitter substances in
hopped wort as 100 per cent, then the other steps in the process cause such great losses that
their quantity in the finished beer is only 20-25 per cent. Most of the loss of bitter substances
occurs in the cooling of hopped wort (due to the adsorption of the bitter substances on the
separated dregs) and during the main fermentation due to changes of pH value, adsorption on
yeasts, and the removal of bitter substances in foam layer. Further losses of bitter substances
occur during the secondary fermentation and in the filtration of beer.
Fig. 1. Hop tokens: a - marking of bales before further procedures.
16
b - certificate of a consignment from Zatec region.
The fall in brewing value during hop storage and heavy losses of bitter substances in the
production of beer are economically unsatisfactory. Therefore these questions are studied
worldwide. They were very intensively investigated especially after World War II. The results
of such research work provided numerous solutions which have been widely adopted in the
brewing industry.
THE PRODUCTS OBTAINED FROM HOP CONES
Various modifications of hop cones have been used in breweries in many countries. Such
modifications include hop extracts and ground or granulated hop cones. Hop extracts were
used to a small extent in Czechoslovakia as early as 1960, but the use of ground or granulated
hop cones did not occur in Czechoslovak breweries until 1970.
Hop extracts
There are two main types of hop extracts:
a) hop resin extracts (one stage type);
b) standard hop extracts (two stage type).
The group of two stage extracts have different ratios of resin to water.
One stage hop extracts consist almost solely of hop resins. The principle of one
stage extraction involves the extraction of hop cones by a suitable organic solvent such as ethyl
ether, methyl alcohol or methylene dichloride. After the completion of extraction the organic
solvent is removed under vacuum and the resultant resins are filled into metal containers.
This type of hop extract was tried out in Czechoslovak breweries where it was shown that it
can replace up to 20 per cent of hop cones without changing the taste of beer. The extract does
not contain tannin, and therefore, it did not find wide application in Czechoslovakia.
However, it is used in many foreign breweries.
The Research Institute of the Brewing and Malting Industry in Prague developed its own
17
