Influence of pre‐drying storage time on essential oil components in dried hops (Humulus lupulus L.)

Abstract

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.

Impact of Process Parameters and Bulk Properties on Quality of Dried Hops

“…Low temperatures such as 50 • C have shown to retain maximum linalool content as compared to those at 65 • C [47]. Similar losses in linalool content were observed for the Mandarina Bavaria variety dried at 60 • C [17].…”

“…To capture the images, an RGB Camera (model no. 61BUC02, The Imaging Source Europe GmbH, Bremen, Germany) was placed at a distance of 29 cm from the surface of the product [17] using the camera window of the photo box. A schematic of the imaging system used is presented in Figure 3.…”

“…Myrcene, linalool, ß-caryophyllene and humulene-representing the most valuable oils related to Hallertauer Tradition-were the main components analysed in the GC unit. Mathematical calculation for quantity of hops required for distillation of essential oils was determined using the method described in [17].…”

“…The inclusion of a higher number of small cones resulted in faster drying but also led to the formation of air pockets or so called "nests" within the drying chamber which in turn led to uneven drying [10]. Investigations performed on storage of hops revealed that hops stored for a longer amount of time undergo oxidation which lead to formation of compounds that interfere with the aromatic smell associated with hops [17]. Bulks with unevenly distributed moisture content can also undergo a similar degradation and thus leading to significant losses of both physical and chemical attributes of the product.…”

“…Within the current investigation it was observed that increasing the drying temperature decreased the total amount of oil extracted after drying. An investigation performed on the Mandarina Bavaria variety of hops revealed losses in the total oil extracted after drying as compared to prior to drying [17]. Furthermore, drying of Laurel (Laurus nobilis L.) leaves at either 45 • C or 65 • C accounted for losses close to 83% [39].…”