Pure hops-derived substances were added to unhopped beer. Illumination only produced a sun-struck flavour with cfs-isohumulone, trans-isohumulone and racemic trans-isohumulone. It seems that 3-methyl-butenyl-mercaptan is not or not alone responsible for sun-struck flavour.Tests trials show that trans-isohumulone, cis-tsohumulone, racemic trans-iso humulone, trans-pt-isohumulone and ds-^-isohumulone do not show significant differences in bitter taste and bittering power. Fresh solutions of these bitter acids are not as bitter as solutions which have been kept for a few weeks.Since it is known that the isomerization of compounds in question is not easy as only humulone produces two diastereo-isomers,6toms-isohumulone is crystalline with in.p. namely trans-and cts-isohumulone,* the 08°C. and can thus be purified completely question of their relative bitterness is clearly by recrystallization. The cts-isohumulone important. The interesting point behind is an oil and even the most careful work this is obviously that if one of the two isocannot produce it completely pure. It mers is more bitter, industrial isomerization cannot be distilled without decomposition conditions could be adapted to produce more and partition procedures like chromatoof the more bitter iso-a-acid. graphy or countercurrent distribution, alOver a very wide range of pH, aqueous though producing highly purified material, alkaline isomerization gives the same equilido not yield completely pure substances, brium mixture with a ratio 65-70/30-35 for Indeed, these procedures yield the desired the cts-and /rans-isomers.' Magnesium catasubstance in dilute solution and the evaporalysed isomerization, however, produces a tion of the large excess of solvent always 50-50 mixture.4Photo-isomerization* in leaves some impurities behind. Also, it is methanol leads to a high percentage of the very difficult to remove the last traces of frans-isomer.solvent from an oil like cts-isohumulone. A comparison of bitterness for the two These observations are general for the field • Trans-and ei's-isohumulone are new names for isohumulonc A and D respectively according to the nomenclature proposals ol the Hops Liaison Committee of the E.B.C.

Hydrogen gas, formed in bottled beer during the action of beer on the aluminium spot of the crown cork, may promote gushing, if the beer initially has a high content of dissolved nitrogen. If under otherwise similar conditions, however, this initial nitrogen content is low, no gushing is observed. Thus the presence in beer of relatively large amounts of dissolved nitrogen and hydrogen can be considered as a potential cause of gushing. As high contents of dissolved nitrogen in beer may be due to an insufficient after‐fermentation, this accordingly may contribute to gushing.