Addition of Hops

Carbohydrate Composition of a Typical Wort Obtained after Mashing and Lautering 

For production of lagers, the fermentation process is carried out at 7°C to 15°C for 8 to 10 d, and for Pilsners at approximately 20°C for 3 to 5 d. Lagers are almost always fermented with bottom yeast, whereas Pilsners are always fermented with top yeast. Most beers are kept in closed tanks at a temperature of 0°C for 4-6 additional 

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The sesquiterpenes caryophyllene and humulene react with elemental sulphur under mild conditions to produce the episulphides (87), (88), and (89) [52]. The level of these compounds is higher in oil prepared by steam distillation at 100°C than in oil obtained by vacuum distillation at 25 C. Thus, higher levels of these compounds are likely to be introduced into beer by late addition of hops to the copper than by dry hopping. Myrcene reacts with sulphur less readily, but with a suitable activator a mixture of at least 10 products is obtained of which (90) is the major constituent present in hop oil. 

Hop oil contains a series of thioesters (Table 13.7) the combined amount of which in steam-distilled hop oil usually exceeds 1000 ppm. The level of thioesters in the oil does not appear to be affected either by treatment of hops with elemental sulphur on the bine or by sulphur dioxide kilning [50]. Thioesters are formed in hops largely by the action of heat, so low levels will be introduced into beer by dry hopping. Few sulphur volatiles survive 60 min of wort boiling but after late addition of hops to the copper most of the sulphur compounds discussed above are present in the wort including the thioesters. During fermentation dimethyl trisulphide and some of the thioesters disappear but some sulphur volatiles survive into the finished beer S-methyl 2-methylbutanethiolate is the principal thioester to survive. This last ester and 5-methyl hexanethiolate, the thioester with the lowest taste threshold, are the major thioesters introduced into beer by dry hopping [50]. 

Other instances, the aroma arising from essential oils of hops is provided by direct addition of hop oil or emulsion of essential oils of hops (Chapter 13). 

There has been some debate concerning the occurrence of hop oil constituents in beer (see Chapter 13). Obviously some constituents will go into solution in beer that is dry-hopped but in the copper few components will survive the full period of wort boiling. Consequently many brewers make late additions of hops to the copper. Analysis of a Bavarian beer so treated, which... 

Some of the dimethyl sulphide in barley and malt is oxidized to dimethyl sulphoxide (CHg-SO-CHa) together with a trace of dimethyl sulphone (CH3 S02 CH3). Malt contains 1 42-3 7 ppm of dimethyl sulphoxide. Yeasts are capable of reducing dimethyl sulphoxide back to DMS and this may be one source of DMS present in finished beer [116]. Late addition of hops during wort boiling also contributes dimethyl sulphide, and dimethyl trisulphide, to wort. 

Wort boiling with hops or hop products is done in a brew kettle (hop kettle) in which the initial and subsequent worts from the lautering step are collected. Addition of hops is adjusted according to the type and quality of beer desired. The quantity (in hop cones/hectoliter) for fight lager beer is 130-150 g for Dortmund-type beer, 180-220 g for Pilsener beer, 250-400 g for dark Munich beer, 130-170 g and for malt beer and dark bock beer, 50-90 g. The critical factor is the content of bitter substances in the hops selected. The utilization of the bitter substances (a-acids) is only 30-35%. 

Modern breweries rely heavily on automated procedures. While the addition of hops in their natural state does not lend itself to automation, extracts may be dosed by suitable metering pumps. This, coupled with the standardisation mentioned above, allows fully automatic addition to wort. 

In addition to the bitter acids and essential oils, the flowers of hops offer a rich array of polyphenolic compounds, primarily chalcones and their accompanying flavanones, many of which are prenylated derivatives (Stevens et al., 1997,1999a, b). The most prominent flavonoid in all plants studied was xanthohumol [342] (3 -prenyl-6 -0-methylchalconaringenin chalconaringenin is 2, 4, 6, 4-tetrahydroxychalcone) (see Fig. 4.11 for structures 342-346). Several additional chalcones—variously adorned with 0-methyl and/or C-prenyl functions—were also encountered, along with their respective flavanones. Three new compounds were described in the Stevens et al. 

A sample of hops which had been treated with tetraethyl pyrophosphate showed a negative chemical analysis. The plant material was also extracted and the extract added to the drinking water of test animals and sensitive insects. The animals and insects that drank this treated water for several days showed no reaction. With the sensitive insects it would have been possible to detect even a few parts per million. In addition, there have been extensive commercial field applications of the chemical in dust and spray form to crops such as apples, pears, grapes, celery, broccoli, Brussels sprouts, and others up to within a few days of harvest there has been no detectable poison residue on any of the crops. The lack of poison residue with use of tetraethyl pyrophosphate is due to the fact that it hydrolyzes within a few hours of application, breaking down into transient nonresidual and nonpoisonous chemicals. Thus it is possible to use tetraethyl pyrophosphate well up to harvest time of food products without danger of residual poison on crops. The fact that the chemical is used in extremely small amounts is a definite advantage in respect to freedom from poison residue. 

One of the exciting new directions is the control of activated rate processes using external fields. Addition of an external field opens the way for a wide variety of new phenomena such as stochastic resonance, resonance activation, directed transport, control of the hopping distribution in surface diffusion and more. Even the addition of a constant force to the problem leads to interesting additional phenomena such as the locked to running transition, which remains a topic of ongoing research. " Quantum mechanics in the presence of external fields may differ significantly from the classical. 

Heterotrophic bacteria have the ability to incorporate not only inorganic N but also dissolved inorganic P into organic material. Additionally, as microbes have extremely high P content relative to plants or even phytoplankton (Kirchman, 1994), HOP may be expected to be at least as or even more important than HON. Studies in lakes and marine systems support the importance of HOP in forming new organic P in aquatic systems (Kirchman, 1994). 

The implications of HOP for quality of organic matter, including quality of DOM, are similar to those of HON (discussion below) as the P content of organic material is often cited as an important determinant of organic matter quality (Sterner, 1995). HON has additional implications for stable isotope research, however, that do not apply to HOP. 

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