Asymmetrische Diels-Alder-Reaktionen von Trans-1,3-Pentadien und Cyclopentadien mit Chiralen Acrylsaeure-Derivaten

SIGLEAvailable from TIB Hannover: DW 3194 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Impact of bulk weight on drying behaviour and hop quality after drying

Hops are a key ingredient for beer brewing due to their role in the creation of the foam characteristics, bitterness of the beers and aroma. Whilst in the past foam and bitterness were the key characteristics sought by the market, the last decade has seen a steep increase in demand of aroma hops for the production of crafts beers. Color of the final product plays a major role in quality perception of traders and brewers. Therefore, color changes were investigated to estimate the impact of bulk weight and thus drying time and conditions on the upper surface of the bulk. A calibrated imaging system consisting of a CCD camera and illumination was integrated into the dryer. Further, changes of and ß acid contents were investigated. Hops of the variety Mandarina Bavaria were dried at 65°C and an air velocity of 0.35 m/s. Bulk weights investigated were 12, 20 and 40 kg/m² respectively. Drying times were 105, 135, and 195 min. Drying characteristics showed a unique development which very likely is due to the distinct physiology of hop cones (string, bracteole, bract, lupilin glands). Color changes depended strongly on the bulk weight and resulting bulk thickness whilst a and ß acid contents were not affected by the drying conditions. The research presented showed that air mass flow in relation to the mass of water to be removed is critical for the quality of the product as well as the processing time required

Measurement of hop moisture content and chromaticity during drying with VNIR hyperspectral imaging

The drying of hops is a crucial post harvesting stage in the production of beer. If hops are not dried to below a specific moisture content they will spoil prior to being processed into pellets for beer production. Further to this, drying of hops is usually undertaken by farmers themselves, and with a single harvest per year the drying operation is of great economic importance for their survival. The monitoring of moisture content is usually undertaken through moisture and humidity sensors placed within the hops themselves. However this method leads to the sampling of moisture content in specific spots, and as such relies upon drying uniformity. Furthermore the moisture content of the hops at the input stage varies greatly with environmental conditions. Optical methods with 2D sensors offer the opportunity to monitor moisture content changes across the entire drying area. With hyperspectral imaging allowing investigations to uncover the most important wavelengths related to moisture content. To investigate this Mandarina Bavaria hops were imaged during the drying process in-situ using a hyperspectral camera (Specim PFD-V10E) across the 400-1000nm region. Drying was undertaken at two temperatures (65, 70°C), with three different bulk weights (12, 20 and 40 kg/m²) and at two air speeds (0.35 and 0.50-0.35m/s). This was to introduce variation into the model to allow fully characterisation of spectral changes of hops during drying. Investigations have shown that a simple optical system using a small number of wavelengths can be used to estimate hop moisture content and chromaticity

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

BACKGROUND: It is well known that duration of pre-drying storage impacts on hop quality. However, little knowledge existsregarding its actual effects on valuable hop components. To investigate these effects, fresh hop cones were stored for 5 or24 h and dried for 210 min at 65 °C thereafter. Furthermore, to understand the effect of freezing hop cones on the essentialoil content, both fresh and stored samples were frozen before and after drying. RESULTS: The results from gas chromatography analysis show an increase in linalool, -caryophyllene, humulene, geraniol con-tent and decrease in myrcene content dependent on the period of storage. Total colour difference ∆E values of 4.61 and 5.27were obtained for fresh and stored hops respectively, indicating discoloration of hops during storage. Modelling of moisturecurves revealed the Wang and Singh model to be suitable, with R2adjvalues of 0.978 and 0.989 and root-mean-square errorvalues 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 conesboth during storage and drying and will further help hop processors optimize their storage times