Deteriorated hops were extracted with liquid carbon dioxide (LCO2) and with ethanol. The degree of hop deterioration influences both the extraction efficiency and the composition of the resulting extracts.
The time course of the extraction of a-acids by liquid carbon dioxide was investigated and it has been established that there are two zones with greatly differing rates of extraction. The rate in the first zone is governed by 'solubility' effects, while in the second zone the rate is limited by 'diffusions!' effects. Consequently the rate of extraction in the first zone depends upon the flow rate of liquid carbon dioxide while that in the second zone depends upon the time of extraction. The effects on extraction performance of the depth of the bed of hops and the extent of milling were also explored.
The quality of beers bittered with liquid CO2 and ethanoi extracts derived from fresh and deteriorated hops and the percentage utilization of alpha-acids therefrom were comparable. The importance of using analytical methods which measure bitterness substances per se is emphasized.
The time‐course of liquid carbon dioxide extraction of fresh and deteriorated hops was compared. The process of extraction becomes more difficult as hops deteriorate, which is reflected by the reduction in the LCV yield (g LCV/kg liquid carbon dioxide used). The extracts derived from deteriorated hops contain higher levels of uncharacterised soft resin. The pattern of elution of the latter does not allow the production of extracts low in uncharacterised soft resins and rich in alpha‐acids.
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