One of the qualitative characteristics of both green and dried hops is the content of hop essential oils which are contained in a quantity of 0.5 to 3.5%, depending on the hop variety. These essential oils are heat labile substances because the temperature has an influence on their content. Hop cones, dried either in belt or chamber dryers, are exposed to a drying medium temperature of 55 °C to 60 °C for the entire duration of drying, i.e. for 6–8 hours. Under current drying conditions there is a loss of approx. 15 to 25% of the total content of essential oils present in hops before drying. In case of special aroma hop varieties, such losses lead to a decline in the product quality. Comparative measurements have been carried out with a laboratory equipment to find out whether more aromatic essential oils are retained in hop cones at a drying temperature of 40 °C compared to a drying temperature of 60 °C. The measurement carried out with the most common variety of Saaz hop concluded that the essential oil losses were lower by 33.4% at a drying temperature of 40 °C, and with other seven mostly hybrid varieties the losses were lower on average by 13.9% than at a drying temperature of 60 °C. The measurements proved that each of the varieties retained, to a significant extent, its content of essential oils in the dried hop cones at a drying temperature of 40 °C.
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