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

Abstract

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