Supercritical hops extract

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. 

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. 

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... 

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. 

Extraction with supercritical CO2 is a technical process of increasing importance. It provides a mild and rapid technique for the extraction of low- or medium-polarity substances. Supercritical CO2 is used for supercritical fluid extraction (SFE) in important technical processes such as the decaffeination of coffee and the extraction of hops, as well as the extraction of naturally occurring compounds from biomaterials. As many applications are performed in the pharmaceutical, polymer, environmental and nutritional fields, direct on-line SFE-NMR would be an ideal tool to monitor the various extraction processes. 

Based on its ability to enhance solvating power by increasing fluid density, supercritical fluid extraction offers an attractive alternative for fractionation of fats and oils. It works by the phenomena of selective distillation and simultaneous extraction, as has been shown by many researchers [3-5]. While the use of supercritical fluids in the extraction of numerous biomaterials has been reported, its commercialization has been limited to the decaffeination of coffee and tea and to the extraction of flavors from hops and spices. The chemical complexity of most food ingredients and their tendency to react and degrade at elevated temperatures, emphasize the difficulties of supercritical solvent selection. Carbon dioxide is the preferred supercritical solvent (its properties have previously been cited [6]). 

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]. 

Energy costs K for supercritical fluid extraction of hops with C02 according to Process 1. 

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. ... 

Supercritical fluid extraction has now found a lot of applications in different fields (polymers, aromas and essential oils, fats, natural products, soil decontamination...) and several production units are operated in agroalimentary (coffee, hop...) and pharmaceutical industries. In order to estimate the economical interest of these applications, technical and economical extrapolation methods have been developed. These methods are dependent of the nature of the extraction and are based on experimental results obtained on pilot plant units. We describe here a general extrapolation procedure, and a case study is presented to illustrate an economical estimation of a supercritical fluid extraction. 

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... 

Water has been shown to be an effective solvent in some chemical reactions such as free radical bromination. Supercritical fluids such as liquified carbon dioxide are already commonly used in coffee decaffeination and hops extraction. However, supercritical carbon dioxide can also be used as a replacement for organic solvents in polymerization reactions and surfactant production. Future work may involve solventless or neat reactions such as molten-state reactions, dry grind reactions, plasma-supported reactions, or solid materials-based reactions that use clay or zeolites as carriers. 

The attractiveness of supercritical carbon dioxide extraction is shown by the already existing industrial applications of hop extraction, decaffeination of tea and coffee, defatting of cocoa powder, and extraction of herbs and spices and is also demonstrated by the large number of patent applications and scientific publications in recent years. 

F. David, P. Sandra, W. S. Pipkin, and J. Smith, Supercritical Fluid Extraction of Hops, Application Note 228-115, Hewlett-Packard Company Publication No. (43)5952-2342 (1990). 

All these items must be specified and they all affect capital and operating costs. We have mentioned product cost several times in this book, but we do not mean to imply that product cost is the most important factor to be considered. As we related in chapter 7, there are hop extraction plants in operation, and hop extract sells for 30 per pound yet there are also many propane deasphalting and residuum extraction plants in operation, and these petroleum products sell for only 10 cents per pound. These two products are on the opposite ends of the commodity spectrum, and their respective processes represent the potential breadth of application of supercritical fluid technology. 

A later patent assigned to the Brewing Patents Limited. Laws, D. R. J., N. A. Bath. C. S. Ennis, J. A. Pickett, and A. G. Wheldon, Production of an Iso-Alpha-Acid Preparation from Hops, U.S. 4,298,626, Nov. 3,1981, describes the isomerization of the alpha-acids obtained by CO2 extraction. It describes the advantages of using a supercritical CO2 extract in the subsequent isomerization process. 

Initial commercial applications of supercritical fluids were coffee decaffeination (in 1978) and hops extraction (in 1982). Together, these uses accounted for over half of the world s supercritical fluid production processes in 2001 (Figure 8.9). 

Not every pharmaceutical will eventually be comminuted by supercritical fluid nucleation, not every polymer processed for molecular weight control by supercritical fluid extraction, not every flavor concentrated by supercritical fluid extraction but some will be. Two applications listed in the table are already in commercial production, and several are in advanced pilot plant development and test market evaltiation. Hops extraction is being carried out by Pfizer, Inc. in its plant in Sydney, NE (33), and General Foods Corporation has constructed a coffee decaffeination... 

Much of the commercial interest has been in the food and pharmaceutical industries. Here, the major driving force is the desire to have conpletely natural processes, which cannot contain any residual hydrocarbon or chlorinated solvents tHumphrey and Keller. 19971. Supercritical carbon dioxide has been the SCF of choice because it is natural, nontoxic, and cheap, is conpletely acceptable as a food or pharmaceutical ingredient, and often has good selectivity and capacity. Currendy, supercritical CO2 is used to extract caffeine from green coffee beans to make decaffeinated coffee. Supercritical CO2 is also used to extract flavor conpounds from hops to make a hop extract that is used in beer production. The leaching processes that were replaced were adequate in all ways except that they used solvents that were undesirable in the final product. 

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