Wort boiling

Fig. 7. Wort boiling ketde with external heating calandria. The wort is pumped from the bottom of the ketde through the calandria and thence back into the ketde through the so-called fountain. This circulation and heating may be started as soon as enough wort is in the ketde to fill the system. The directed...

The extraction of the bitter substance of hops is a complex process. During boiling and subsequent fermentation, large losses of bitter substances are incurred, and only 25—30% of the bitter substances in hops are present in the finished beer. The amount of loss depends on composition of the wort, pH, etc. Much of these bitter substances is adsorbed by the warm sludge and is lost during its separation. Wort boiling takes place in the wort kettle or copper of various constructions. An example appears in Figure 7. 

Consist of haze, which form either during wort boiling or cooling, and which is removed before fermentation. 

This long wort boiling time is Important in that most of the mass (80-90%) of typical hop oil is made up of terpene and sesquiterpene hydrocarbons which are either steam distilled out of the wort, polymerized or oxidized to more water soluble compounds during the process (, 5, 11, 12). As a result, these hydrocarbons are not found in beer (, 5, T) and therefore are not responsible for this flavor. Investigators in this field do agree that this... 

At present there is little agreement as to what compounds are responsible for "kettle hop" aroma. The theory of Peacock and Deinzer ( ) that it is humulene oxidation products seems most in agreement with the traditional prejudices of brewers. Long hop storage, long wort boiling times and a high concentration of... 

Of these constituents, the resins and essential oil are peculiar to the hop and are responsible for its brewing value. In wort boiling tannins, sugars, amino acids, and proteins derived from the hop will go into solution and react as discussed in Chapter 14 but in general the larger proportion of these constituents in beer will be derived from malt. The chemistry of the resins and essential oil will be discussed in this chapter. During wort boiling, the a-acids are isomerized into iso-a-acids but discussion of this most important reaction is deferred until Chapter 14. 

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]. 

Only small amounts of hop-oil constituents go into solution at wort boiling and much of this material is lost or transformed during fermentation. In many samples of American beer it was concluded there were insufficient hop-oil constituents to affect the flavour, but one commercial beer with a pronounced hop aroma contained 1079 ppb hydrocarbons (970 ppb myreene) and over 42 ppb oxygenated components [56]. Transesterification of hop oil esters occurs during fermentation, thus methyl dec-4-enoate and methyl-deca-4, 8-dienoate present in hopped wort were converted into ethyl dec-4-enoate and ethyl deca-4, 8-dienoate in beer [57]. 

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