A mechanical pruner serves for pruning new hopvine shoots in spring. The later yield depends on the right timing and quality of pruning. That is why hop pruning is one of the most important agrotechnical procedures. A double-disc mechanical pruner used on high trellises cannot be used on low trellises due to its large size. Abroad, for pruning hops on low trellises a specially adapted sprinkler is used (chemical pruning). With regard to the effort to minimize the chemical environmental burden, we opted for the design of the mechanical pruner. Firstly, the low trellis, mechanical pruner, and also elements used in the design of hydraulic circuit are described. Next part of the paper is devoted to the input requirements for both the hydraulic circuit and the mechanical pruner designs. Then a description of an adapted inter-axle carrier used for the experimental model of the hop mechanical pruner and of the effected field measurement follows, along with interpretation of the measured data. These data are depicted in clearly arranged graphs showing the dependency of pressure and hydraulic oil flow on the cutting disc rotational frequency.
The article summarizes the results of a two-year research focused on separating impurities in hop picking line by means of inclined belt conveyors. Researchers designed a new version of inclined belt conveyors which were installed in one segment of a parallel hop picking line. In the other segment the current inclined belt conveyors remained. Regarding the product quality, better results were obtained with new inclined belt conveyors where the average content of impurities at the output was 7.73%, contrary to the treatment with current conveyors where the content of impurities was 12.03%. The current inclined belt conveyors had 4.8 times higher losses of hops than the new ones. The economic assessment clearly proves the use of new inclined belt conveyors to be more effective, as the return of the costs for the exchange of six inclined belt conveyors in a picking line makes only 3.13 years at a comparable or even better quality of separation.
Rybka A., Heřmánek P., Honzík I., Krofta K. (2017): Parameters of the drying medium and dried hops in belt dryer. Res. Agr. Eng., 63 (Special Issue): S24-S32.An important factor in hop growing is the process of drying. For this purpose belt dryers with follow-up conditioning are the most widespread but they are not ideal. In this respect, an analysis of the drying process was carried out in the belt dryer of Agrospol Velká Bystřice Co., Ltd. for the 'Saaz' hop variety. Drying parameters were monitored by means of fixed sensors, continuously sensing data loggers and samples taken for laboratory analysis (hop moisture, alpha and beta bitter acids, Hop Storage Index (HIS). The process of drying showed that hops are practically dry (10 ± 2.0% of moisture) already at the end of the second belt or possibly at the beginning of the third belt. It was also proved that hops are over-dried (moisture of 4 to 8%) and then they are adjusted by conditioning to the final moisture content of 8-10%. Excessive drying leads to cone disintegration, which makes any manipulation with hops for purposes of further processing difficult and results in greater losses of lupulin. The current state in the field of technology of hop drying and conditioning is not ideal. This refers to both operating costs and qualitative features of the final product. In belt dryers prevailing so far, following stationary picking lines, their drying process is directly linked to the continuous process of harvest. In belt dryers hop cones are dried at a drying air temperature of 55-60 o C for 6-8 h coming from original 75-85% of moisture to final 8-10% prior to conditioning. Bracts themselves, however, have moisture content of only 5-6%, while strigs may have a moisture content of up to 30%. Percentage of strig weight to the total cone weight (6-12%) has a great effect on subsequent moisture permeability during the conditioning of hop cones (Kořen et al. 2008). Controlled conditioning requires roughly up to a 1/3 of the total energy requirements needed for hop growing (Doe, Menary 1979). Stability of alpha bitter acids, being the key hop substance from the point of view of brewing technology, is sufficient at drying temperatures reaching up to 60°C. However, for some heat-labile substances the drying temperatures between 50 and 60°C in the final stage of drying are too high. They lead to irreversible transformations and losses. Such substances are for instance hop essential oils that are contained in the amount of 0.5-3.5%, depending on hop variety (Hofmann et al. 2013;Kumhála et al. 2013). The pilot studies showed a decrease of 15 to 25% of the overall content of essential oils present in the hops prior to drying at the current drying conditions (Kieninger, Forster 1973;Kirchmeier at al. 2005). Besides this amount, the sensory profile changes too, due to a loss of the more volatile components. With special aroma hop varieties, so called "flavour hops", whose 25Vol. 63, 2017, Special Issue: S24-S32 Res. Agr. Eng.doi: 10.17221/35/2017-RAE content and ...
In terms of content, the paper is aimed at analysing and comparing the quality of fresh green hops and hops dried at two drying temperatures – 55°C (in the traditional manner) and 40°C (using the so-called gentle drying), regarding the maximum preservation of hop essential oils. Comparative experiments were carried out in an experimental chamber dryer with two Czech hop cultivars Saaz and Harmonie. The moisture content of hops at the beginning of drying was 75% and at the end of drying it was 9–10%. By lowering the drying temperature from 55°C to 40°C, the drying time in cv. Saaz prolonged from 8 to 10 h and for the cv. Harmonie from 9 h to 12 h. Compared to fresh hops, the amount of hop oils decreased by 10% when dried at 40°C and by 36% (cv. Saaz) and 43% (cv. Harmonie) when dried at 55°C. These losses can be considered significant, especially for hops intended for late and dry beer hopping. However, by drying the hops at different temperatures, the ratios between various components of the essential oils and thus also their sensory character remained approximately unchanged. Due to the reduced amount of essential oils, the drying effect reduces the intensity of hop aroma depending on the drying temperature.
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