Zinc Is determined colorimetrically in beer and brewing materials by means of di‐beta‐naphthylthiocarbazone. This reagent forms a complex with zinc which is soluble in carbon tetrachloride giving a cherry‐red solution. The zinc is determined by the mixed colour method of colorimetry, using a light filter with maximum transmission at 5,500 A. Interfering metals are removed by a preliminary extraction as diethyl‐dithiocarbamates. The range covered by the method is from 0 to 16 μgrn. of zinc, enabling determinations to be made of as little as 0.01 p.p.m. of zinc in liquids or 0.05 p.p.m. in solids.

The techniques of gas‐liquid chromatography and nuclear magnetic resonance allow simultaneous analysis of the individual α‐acids and β‐acids and the corresponding 4‐desoxyhumulones. The rates of appearance in the growing hop‐cone of humulone, lupulone, 4‐desoxyhumulone and their co‐homologues and ad‐isomers are reported. The results indicate a relatively enhanced initial formation of the 4‐desoxy compounds and β‐acids. The α‐acids reach their maximum concentration later than the desoxyhumulones and β‐acids but eventually become the predominant group. It appears that formation of the α‐acids is associated with a decline in the relative proportion of both β‐acids and 4‐desoxyhumulones. For each class of compounds, the co‐homologues increase their relative concentrations during the growth of the hop; adhumulone and adlupulone remain in almost constant proportions during this period.

Previous studies on the 4‐desoxyhumulones in hops using classical methods indicated that these substances may account for up to 0·05% of mature Hallertau hops. 4‐Desoxycohumulone and 4‐desoxyhumulone are now shown to be detectable directly, and simultaneously with the α‐acids and β‐acids, by gas‐liquid chromatography of their trimethylsilyl ethers; identification has been confirmed by mass‐spectrometry. Quantitative analysis is possible by use of standard 4‐desoxycohumulone, conveniently prepared by ultraviolet irradiation of colupulone. This indicates that the concentration of the 4‐desoxyhumulones is in fact around 0·3% of mature hops—seven to ten times the previously reported concentration.

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