Hops extraction

The use of hops in the form of hop extract has spread rapidly the yield of the extract is better, yet insufficient. The production of a satisfactory hop extract quahty, ie, no taste difference to beer hopped by using other "natural" hop products, has appeared to be a science or art in itself Use of the right solvent and distillation is the key point, and many unsuccessful attempts have been made. The latest and most successful method, using the so-called Hquid carbon dioxide extraction, meets the high quaUty demands almost perfecdy. Preisomerization of the resins makes it uimecessary to boil them with the wort they can be added directly to the finished beer to avoid poor yield (through boiling) and the loss of resins (during fermentation). 

The separation of hops from the boiled wort has been accelerated by the use of hop pellets or hop extract. The wort is transferred directly from the wort kettle to a whirlpool where the hops are separated along with the hot sludge. Whirlpools have become popular because of their low operating costs. 

Trichloroethylene was approved for use for many years as an extraction solvent for foods. In late 1977, the Eood and Dmg Administration (EDA) harmed its use as a food additive, direcdy or indirecdy, prohibiting the use in hop extraction, decaffeination of coffee, isolation of spice oleoresins, and other apphcations. The EDA also harmed the use of trichloroethylene in cosmetic and dmg products (23). 

Supercritical carbon dioxide (SCCO2) is a well-estabhshed solvent for applications in extraction processes. During the last 40 years, there has been an implementation of large-scale processes, e.g., the extraction of caffeine [6] and the isolation of hop extracts from raw plant material [37]. These examples show that the usage of this supercritical fluid (pc = 73.8 bar, Tc = 31.1 °C) is a state of the art operation in process technology. 

Much of the interest in SFE has been focused on using carbon dioxide to extract different natural products from solid materials. Examples of large industrial processes in this area are decalfeinating coffee beans and hop extraction. 

In the United States, dichloromethane may be present as an extractant or process solvent residue in spice oleoresins at a level not to exceed 30 mg/kg [ppm] (including all chlorinated solvents), in hops extract at less than or equal to 2.2% and in coffee at a level not to exceed 10 mg/kg [ppm] (United States Food and Drug Administration, 1996). 

The second largest application is in the extraction of hops. In the last twenty years nearly all producers of hop extracts have changed to the supercritical extraction process. Even in the Eastern European countries the methylene chloride process was stopped several years ago. 

Figure 8.1-13. Production cost for hop-extraction under different processing conditions dependence on processing-weeks.

Extraction of hops can also be achieved under liquid conditions (preferably 72 bar, 20°C) with production costs about 10% lower compared to the process with the supercritical condition (extraction pressure 350 bar, separation pressure 45 bar). However, because hops-extraction plants are operated only four to six months/year, extractions under supercritical conditions are preferred, as such a design provides more flexibility, by allowing the processing of other materials such as tea or cocoa... 

Now nearly all hop-extraction plants operate with C02. In principle, it would be possible to reach the desired limits and to meet public health requirements with respect to level of residual solvents, but some solvents such as methylene chloride are always subject to doubt and public discussion. 

Above 400 bar, most of the hard resins are extracted. At 300 bar and 80°C the solubility of hops-extract in C02 is around 3.2%wt. The supercritical extraction has many advantages compared to the subcritical extraction, so that even though the investment costs are higher, all new plants have been built for supercritical extraction. 

Because of these advantages the CO2 extraction is a very successful technology for hops, with the result that nearly all hop-extraction plants have changed to the CO2 process in the last twenty years [21]. 

Standardization p-nitroanilide of myri stic acid Calibration hop extract Same as ASBC... 

Scope a-, / -, and iso-a-acids in hop and isomerized hop extracts Iso-a-acids in isomerized extracts Iso-a-acids in isomerized extracts Iso-a-acids in isomerized pellets... 

ACJ Hermans-Lokkerbol, AC Hoek, R Verpoorte. Preparative separation of bitter acids from hop extracts by centrifugal partition chromatography. J Chromatogr A 771 71-80, 1997. 

Institute of Brewing Recommended Methods. Hops and hop products 6.5. Alpha- and beta-acids in hop extracts by HPLC. 

ASBC Methods. Hops 14. a-Acids and /3-acids in hops and hop extracts by HPLC (International... 

JA Gusinski. Practical considerations of reduced hop extracts. EBC Symposium on Hops, 1994, pp 105-113. 

R Franiau, R Mussche. Quantitative determination of hop bitter substances and their derivatives in hop extracts by thin layer chromatography. J Inst Brew 80 59-67, 1974. 

Plants and plant extracts have been used as medicine, culinary spice, dye and general cosmetic since ancient times. Plant extracts are seen as a way of meeting the demanding requirements of the modem industry. In the past two decades, much attention has been directed to the use of near critical and supercritical carbon dioxide solvent, particularly in the food pharmaceutical and perfume industries. CO2 is an ideal solvent because it is non-toxic, non-explosive, readily available and easily removed from the extracted products. At present the major industrial-scale applications of supercritical fluid extraction (SFE) are hop extraction, decaffeination of coffee and tea, and isolation of flavours, fragrances and other components from spices, herbs and medicinal plants [1-4]. 

Process costs are influenced by various factors which are mutually dependent, so that it is not initially clear which extraction and separation conditions are the most favourable. A large value for AY is favourable, since the yield of hop extract per kg C02 is then high. A low pressure ratio p /p is also favourable, since the mechanical work for compression is then small. Solubility data are however most favourable for extraction when the pressure is high, whilst conditions for separation are most favourable at low pressure. A low initial compressor temperature tt is favourable, since the mechanical work is then small. Too low a temperature, however, requires a refrigeration unit which increases the mechanical work requirement and is thus unfavourable. 

It is found that, for Processes 1 to 3, the most favourable variants generally employ temperatures of 60°C or 80°C. These are the temperatures at which hop extract has its highest solubility at the pressures of 250 and 300 bar. The most favourable variants do not, however, involve the expected separation conditions at the lowest solubility values. At low separation pressure, the solubility is indeed very low, but the pressure ratio p /p and therefore the mechanical work of compression is greater, making such a variant more unfavourable than a variant at higher separation pressure. This applies to the Processes 1 to 3. The most favourable variants are thus often those with a separation pressure exceeding 100 bar. 

Comparison of the three processes reveals that costs scarcely differ between Processes 1 and 2. The costs K of the first ten variants lie in the range 0.014 - 0.017 DM/kg hop extract, whilst the first ten variants of Process 3 cost approximately 0.002 DM/kg hop extract less. It is thus an advantage that the separation temperature in Process 3 is achieved by pressure release alone, without adding or removing heat. Table 2 includes separation temperatures which often considerably exceed 40 °C. 

For purposes of comparison, some supercritical fluid extraction processes have been calculated in which the extract is separated at the subcritical pressure p = 60 bar (Process 4). Such a process corresponds to that in Fig. 1 with the difference that a pump is employed to increase the pressure from state 1 to state 2, since the CO2 is cooled down to 17°C after separation, i.e. is present in the liquid state before the pressure is increased. Even for the most favourable variant with K = 0.062 DM/kg hop extract, the operating costs for this process are significantly higher than for processes employing supercritical separation. They can be reduced significantly by heat recovery with a heat pump as published by Sievers and Eggers 3. ... 

Figure 1. Energy costs K in DM/kg hop extract for supercritical fluid extraction of hops with C02 according to Process 3.

By now, nearly every chemist has had some introduction to the subject of supercritical extraction in one form or another, and it would seem that after scores of papers, newsreleases, and trade journal articles, only so much can be said about the background and early findings, the thermodynamic interactions between dissolved solutes and high pressure gases, the equations of state that can correlate and predict solubility behavior, the many applications of the technology (some of which are in flavors), the full scale coffee and hops extraction plants now in operation, etc. What, then, can a paper entitled "Supercritical Fluids - Overview and Specific Examples in Flavors Applications" give that s new -hopefully, a different development of the historical perspective... 

Due to its unique characteristics and physicochemical properties such as being less toxic, nonflammable, and having the extraction power tuned by temperamre and pressure, SC CO2 can be used as a green solvent for extraction of substances especially from solid or liquid substrates. Such extraction has been carried out on commercial scale for more than two decades and applications like decaffeination of coffee beans and black tea leaves and hops extraction are involved in large-scale processes [17]. Other extractions such as extraction of flavors, spices, and essential oils from plant materials are under investigation. An overview of published data for different materials is given in the review of Marr and Gamse [18]. 

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