Decaffeination process

Fig. 10. Semicontinuous coffee decaffeination process using supercritical CO2 (1).

Decaffeination Regulations. Eor decaffeinated roasted coffee, EEC standards indicate the maximum content of caffeine as 0.1% db for decaffeinated instant coffee it is 0.3% db. In the United States, decaffeination usually signifies that 97% of the caffeine has been removed. Permissible solvents for decaffeination processes are defined by national legislation, eg, EDA or EEC directive. The maximum residual solvent content after decaffeination, roasting, or instant coffee processing is to be kept within good manufacturing practice, ie, very low ppm levels or below at point of sale (46). 

Methylene chloride is probably the most generally used solvent for decaffeination processes, but others, some of which are already found in small amounts in coffee beans, are coming into use. For example, ethyl acetate,8 formaldehyde-dimethylacetal, ethanol, methanol, acetone,9 propane,10 benzyl alcohol,11 carbon dioxide,12 and supercritical carbon dioxide with an acid13 are used. Generally the pressure and temperature of the system are adjusted to keep the solvent in the liquid state. Coffee oil itself is even described for this use in one patent.14... 

Solvent-assisted decaffeination of coffee can result in residues of solvent reaching the consumer.208 The use of chlorinated hydrocarbon solvents such as chloroform,209 methylene chloride, trichloroethylene,208 and difluoromonochloromethane (Freon),210 will probably be replaced by compounds already found in roasted coffee. The use of an ethyl acetate and 2-butanone mixture leaves a 26-ppm residue in green coffee, but zero residue in roasted coffee.211 Other solvent compounds used or suggested for coffee improvement or decaffeination include propane, butane,212 carbon dioxide,213 214 acetone215 dimethyl succinate,2161,1-dimethoxymethane, and 1,1-dimethoxyethane.217 Of all these, supercritical carbon dioxide, ethyl acetate, and methylene chloride are the solvents most used currently in decaffeination processes. 

Other processes beyond the high temperature roasting do not dramatically affect the bean, and with the exception of the decaffeination process, the caffeine content is relatively stable. 

The coffee bean contents of the extractors are discharged and refilled within certain time-periods (6). The decaffeination process is providing the decaffeinated coffee beans as well as the caffeine as valuable products. 

Processes with high mass-flow rates, for example more than 40 t/h, have energy demands of a very high level. Especially for the decaffeination processes, in which several hundred - up to a thousand tons of CO2 are in circulation, isobaric processes were developed. In these processes, the extraction step and the separation step have nearly the same pressure and temperature. The separation of the dissolved substance from the CO2 in circulation is maintained by adsorption on activated charcoal, with an ion-exchanger, or by absorption in a washing column. 

The separation in the isobaric decaffeination processes is executed with absorption of caffeine, that means, the caffeine dissolved in CO2 is carried over into water by means of a packed washing column, or by adsorption with activated charcoal, but without recovery therefrom. Other separation methods under investigation are the use of membranes, since the difference in molecular weight between extract and solvent is high enough, or by the addition of substances of low solvent power. It is questionable whether the advantage of the possible isobaric process can compensate for the investment for the additional process steps required. 

For an isobaric decaffeination process the following data apply... 

As a case-study, the decaffeination process for tea will be considered, where in every case the extraction parameters (pressure, temperature and extraction cycle) are maintained. In the... 

Schoeller-Bleckmann started about 1979 with CO2 extraction and focused his research work in 1983 on decaffeination processes [9,104], From the beginning of this development work great attention was paid to the idea that caffeine can be recovered according to the first process proposed by Mr. Zosel. 

Figure 9.6-2. Flow sheet for the decaffeination process by Schoeller-Bleckmann...

The pre- and after-treatment of the coffee beans is analogous to the usual decaffeination processes. The pre-treatment mainly consists of storing, cleaning and moistening. The moistening is effected by vapour, water, or a combination of both. A water content of 40 to 45% is optimal. After the extraction, the coffee beans have to be dried back to the initial moisture content of 10 to 12%. 

FIGURE 17 Supercritical-fluid extraction in decaffeination process. 

Carbon dioxide gas is a normal component of air. In the carbon dioxide decaffeination process, the gas is raised to a temperature of at least 32°C. Then it is compressed to a pressure of about 7400 kPa. At this pressure, it resembles a liquid but can flow like a gas. The carbon dioxide penetrates the coffee beans and dissolves the caffeine. When the pressure returns to normal, the carbon dioxide reverts to a gaseous state. The caffeine is left behind. 

Figure 10.5 Schematic representation of the coffee decaffeination process.

Figure 1.2 The first semicontinuous solid-supercritical fluid decaffeination process to be developed and commercialized.

In this chapter the SCF processing of two natural products, coffee and edible oils, is described in some detail. The principles involved in the coffee decaffeination process are similar to those described for the regeneration of activated carbon and the extraction of ethanol from water. In the remainder of the chapter a variety of other SCF applications are presented. 

Feb. 17, 1981 4,251,559 Decaffeination process Societe d Assistance Technique pour Produits Nestle SA... 

Sept. 18, 1984 4,472,442 Decaffeination process General Foods Corporation... 

Let us proceed to some of the technical facets of the decaffeination process. Figure 10.1 is a graph of the solubility of neat caffeine in ctu-bon dioxide (Krukonis, 1981a). The solubility of caffeine is about 0.2 wt% at 60°C and 300 bar. The caffeine content of most coffees is about 1 wt%. If, during the extraction process, the caffeine in coffee dissolves to the solubility limit during extraction at, say, 60°C and 300 bar, the amount of carbon dioxide required to decaffeinate coffee is easily calculated. It is 5.0 pounds per pound of coffee. 

This patent on a three step tea decaffeination process is included in chronological order with the coffee patents because of its similarity to U.S. 3,843,824 which describes a three-step process for the decalfeination of roasted coffee. In the first step, tea aromas are removed from dry tea using dry supercritical CO2. In a next step, the tea is moistened and moist CO2 is passed through the tea to extract the catfeine. In a third step the aromas are returned to the moist tea in the following manner. The aromas are dissolved into a sU eam of supercritical CO2 which is then passed first through a heat exchanger to liquify the CO2 and then to the vessel containing the tea which is now dried. When the tea vessel is filled with the solution of liquid CO2 and the aromas vapor CO2 is withdrawn from the vessel and the aromas precipitate into (and onto) the tea. 

For all that, the history of coffee has not come to an end. People liked the social atmosphere of coffee drinking but did not want the possible effect of caffeine, hence the decaffeination process, or of some acids, hence the steam-treatment. For others, making coffee from the roasted beans was too much trouble, hence the preparation of soluble coffees, decaffeinated or not. All these treatments alter the content, and therefore the taste of the beverage. There is now a trend to new products (iced coffee, iced cappuccino for example). There are also gourmet people who buy specialty roasted coffee and increase the side-market for coffee-pots or espresso makers by brewing coffee according to their taste. 

Unhke other decaffeination processes, a product treated with the hyper-crossUnked sorbent was rich in color and very flavorfijl. The ion exchanger and the neutral polystyrene macroporous adsorbent failed to produce similar good results. 

Most recently, genetic engineering opened the opportunity to knock-out caffeine-synthase and eliminate both of the last steps in the biosynthesis, methyla-tion of 7-methylxanthine and theobromine respectively. The goal is to cultivate thereby caffeine-free tea and coffee, without affecting their high polyphenol content as current decaffeination processes do. [511, 512]... 

For case 1, a screening unit of high flexibility and availability is needed. The extraction volume can be small. For case 2 the amount of extract should be apt to determine the course of the extraction with time. It has proved that about 100 to 500 g of solid substrate is appropriate, meaning that the extraction vessel volume should be about 1000 cm If a gas cycle is added, a parameter study can be carried out on extraction and precipitation. For case 3 the equipment should be able to carry out the total process or to simulate all the process steps in sequence in the same manner as intended in a production process. This means that for purposes of screening and a parameter study the precipitation of caffeine in a decaffeination process can be carried out by adsorption on active charcoal or by absorption in water. But for demonstration of process principles, the individual steps have to be carried out by the same unit operation and with the same type of mass transfer equipment as intended for use in a large scale process. Otherwise, no indication of the joint operation can be obtained. For information on scale up, the extractor volume must be at least one order of magnitude larger than in the laboratory type of equipment. 

A third method, the carbon dioxide decaffeination process, is being used with increasing frequency. The raw coffee beans are moistened with steam and water, and they are then placed into an extractor where they are treated with carbon dioxide gas under very high temperature and pressure. Under these conditions, the carbon dioxide gas is in a supercritical state, which means that it takes on the characteristics of both a liquid and a gas. The supercritical carbon dioxide acts as a selective solvent for caffeine, thus extracting it from the beans. 

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