The biosynthesis of humulone, an antibacterial bitter acid from hops, was studied by isotope-incorporation experiments using 13 C-labelled glucose or 2 H 2 O. 13 C enrichments, 2 H enrichments and 13 C 13 C coupling patterns identify isovaleryl-CoA, malonyl-CoA and dimethylallyl pyrophosphate as precursors for humulone. Dimethylallyl pyrophosphate, which serves as a building block for the bitter acid, is generated via the deoxyxylulose pathway of terpenoid biosynthesis. The data confirm that a symmetrical intermediate is involved in humulone formation.

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BACKGROUND It is well known that duration of pre‐drying storage impacts on hop quality. However, little knowledge exists regarding its actual effects on valuable hop components. To investigate these effects, fresh hop cones were stored for 5 or 24 h and dried for 210 min at 65 °C thereafter. Furthermore, to understand the effect of freezing hop cones on the essential oil content, both fresh and stored samples were frozen before and after drying. RESULTS The results from gas chromatography analysis show an increase in linalool, β‐caryophyllene, humulene, geraniol content and decrease in myrcene content dependent on the period of storage. Total colour difference ΔE values of 4.61 and 5.27 were obtained for fresh and stored hops respectively, indicating discoloration of hops during storage. Modelling of moisture curves revealed the Wang and Singh model to be suitable, with Radj2 values of 0.978 and 0.989 and root‐mean‐square error values of 0.037 and 0.019 for fresh and stored hops respectively. CONCLUSION The results from this study provide an in‐depth understanding on the changes occurring within the hop cones both during storage and drying and will further help hop processors optimize their storage times.

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