Production of Hops Extract

Hop is not a stable product and has to be dried immediately after harvesting. During its storage, the a-acid content decrease with time, not as fast when stored under 

Since 1980, the formerly used solvent methylene chloride has been substituted step by step by CO2 processes, covering nowadays over 30% of the hops production. Such plants are located in Europe, United States, and Australia while the first two countries use supercritical CO2, the latter use a process involving liquid CO2. Due to less solvent power, liquid extraction requires more than 50 kg of C02/kg hops in order to obtain the demanded yield of 9 5 wt% for a-acid, although hardly getting any hard resins. 

Independent of design, hops has to be pelletized, increasing the bulk density from about 125kg/m to 500kg/m and reducing consequently the extraction volume in the same extent. 

Hop extracts have the advantage of easier and cheaper storage and transport due to the remarkably reduced volume it can be easily standardized with regard to a-acid content and, consequently, is very easy to dose and maintain the beer quality. 

A comparison between beers brewed with CO2 extracts, hop pellets, or dichloro-methane shows no difference in bitterness and similar long-term stability, but foam values are better if CO2 extracts are used, because precipitation of protein is reduced due to lack of tannins, which forms complexes vhth protein. During wort boiling, a bit of aroma hop pellets are added to increase the polyphenol content and to compensate the slightly less full-bodied note, obtaining thereby an improved stability after maturation. 

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In the food industry, commercial plants with supercritical fluids have so far only been used with supercritical CO2 as solvent. The first plant was opened in 1981 in Bremen (Germany) for decaffeination of coffee, by a process invented in the 1970s by Zosel (1973). Plants for the production of hop extract and for the decaffeination of tea are today also in operation, for example, in Germany, England, and Australia (Voeste et al., 1997). Supercritical hydrocarbons such as propane are also used, for example, for deasphalting of heavy oils or for the removal of triglycerides from fish oils. 

Production of hop extracts 2% if hops added to wort, before... 

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