The historical development of techniques for extracting hops is reviewed and current extraction procedures described and assessed from a technical and commercial viewpoint. Extraction procedures using ethanol and liquid CO2 are illustrated using schematic flow diagrams. Also included in this review are solvent extraction with water, methylene chloride, hexane, trichlorethylene, and methanol. Liquid CO2 extraction produces a purer extract that retains the varietal characteristics of the hop extracted. The process advantages of using CO2 either in a liquid or supercritical state are that it is inert, a good solvent for hop resins, oils and aroma compounds, free of solvent residues, hard resins, fats, waxes, polyphenols and chlorophyll and is easily recovered at low temperatures. Many pesticides are less soluble in CO2 than in organic solvents. Isomerised hop extracts prepared from a CO2 base extract and added post-fermentation provide better hop utilisation and control of beer bitterness and improved foam stability. New specific hop oil fractions and selective fractions of hop resins produced using CO2 extraction technology can be used for brewing speciality beers. In the final analysis it will be the economics of extraction and application that will govern the rapidity with which the transition to increased use of CO2 extracts will occur.
Keywords : extract history hop extract hops process product survey