Dielectric properties of hops – an effect of bulk density

https://doi.org/10.17221/34/2017-RAECitation:Lev J., Kumhála F. (2017): Dielectric properties of hops – an effect of bulk density. Res. Agr. Eng., 63: S18-S23.
download PDF
  Continuous detection of basic physical properties of freshly picked and cleaned wet hop cones would be very helpful for better control and automation of harvesting processes. That is why the main aim of this article was to determine the effects of bulk density changes on dielectric properties of freshly picked hop cones. Relative permittivity and loss factor were measured using a newly developed capacitance measuring device. A strong linear correlation between fresh hops relative permittivity and bulk density was found. This finding could be used e.g. for consequent hop drying process control. Significant differences between tested hop varieties were observed for both relative permittivity and loss factor measurements. These differences cannot be explained only by a slightly different moisture content of the measured varieties and ambient temperature changes. Measured material loss factor was only slightly affected by bulk density changes. However, relative permittivity was affected by bulk density changes significantly. These facts could be used for other properties of wet hop cones estimation.  
References:
ASABE Standards (2008): S358.2 Moisture measurement. Forages. St. Joseph ASABE.
 
FAOSTAT (2016): Food and Agriculture Organization of the United Nations. Available at http://faostat.fao.org
 
Hofmann R., Weber S., Rettberg N., Thörner S., Garbe L.-A. Folz R. (2013): Optimization of the hop kilning process to improve energy efficiency and recover hop oils. BrewingScience, 66: 23–30.
 
KROFTA KAREL, MIKYŠKA ALEXANDR, HAŠKOVÁ DANUŠA (2007): Changes in antioxidative properties of hops in the course of drying, milling, pelletization and storage.. Kvasny Prumysl, 53, 266-272  https://doi.org/10.18832/kp2007014
 
Kumhála F., Lev J., Kavka M., Prošek V. 2016: Hop-picking machine control based on capacitance throughput sensor. Applied Engineering in Agriculture, 32: 19–26.
 
Mejzr J., Hanousek B. (2007): Drying of hop. Research on Agricultural Engineering, 53: 155–160.
 
Nelson Stuart O. (2016): Fundamentals of Dielectric Properties Measurements and Agricultural Applications. Journal of Microwave Power and Electromagnetic Energy, 44, 98-113  https://doi.org/10.1080/08327823.2010.11689778
 
Nelson S.O. (2015): Dielectric Properties of Agricultural Materials and Their Applications. Academic Press, Elsevier.
 
Nelson S.O., Trabelsi S. (2012): Factors Influencing the Dielectric Properties of Agricultural Products and Food Materials. Paper No. 12-1338239. St. Joseph, ASABE.
 
Rybáček V. (Ed.) (1991): Development in Crop Science: Vol. 16. Hop Production. Amsterdam/Prague, Elsevier/SZN.
 
Rybka A., Heřmánek P., Honzík I., Hoffmann D., Krofta K. (2016): Analysis of the technological process of hop drying belt dryers. In: Proceeding of 6th International Conference on Trends in Agricultural Engineering 2016, Prague, Sept 7–9, 2016: 557–563.
 
Oh M., Kim Y., Park J. (2007): Factors affecting the complex permittivity spectrum of soil at a low frequency range of 1 kHz-10 MHz. Environmental Geology, 51: 821–833.
 
J. F. Thompson , M. L. Stone , G. A. Kranzler (1985): Modified Air Flow Rate and Temperature Hop Drying. Transactions of the ASAE, 28, 1297-1300  https://doi.org/10.13031/2013.32427
 
download PDF

© 2020 Czech Academy of Agricultural Sciences