GB2286108A

GB2286108A - A method of preparing coffee beans

Info

Publication number: GB2286108A
Application number: GB9401887A
Authority: GB
Inventors: Surinder Pal Grewal
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-02-01
Filing date: 1994-02-01
Publication date: 1995-08-09
Also published as: GB9401887D0

Abstract

A method of preparing coffee beans by placing them in hot oil at a temperature of approximately 240 DEG C for a time of 65 seconds or so. After cooking the hot beans are quenched in cold water which is removed along with any remaining surface oil in a centrifuge. The beans may be soaked in water before cooking in the oil.

Description

A METHOD OF PREPARING COFFEE BEANS The present invention relates to the preparation of coffee beans, particularly, but not exclusively, to a soaking and/or cooking or "roasting" step before they are ground.

Roasting green coffee beans releases various complex volatile ingredients, of which there are approximately 800, which give roast coffee its characteristic aroma and flavour.

Currently there are various ways of roasting the coffee, often divided between the non-fluidised and the fluidised bed roasting methods.

Conventional, non-fluidised bed roasting uses hot air at temperatures of approximately 5009C. Rotating cylindrical drums are used as roasters. They have paddles in them which constantly turn the charge of green coffee beans in a flow of hot air which passes through them. It takes approximately seven minutes to roast the beans at a bean temperature of approximately 200 to 210it.

Fluidized bed roasting of coffee is described in document US-A-4,169,164 (Hubbard et al.) with a two stage fluidized bed roasting process. The temperature in the first stage is from 226 C to 243 C whilst the second stage is at a temperature between 268 &commat; C and 285'C.

Similarly, document US-A-4,737,376 (Brandeline et al.) describes two stage bed roasting of coffee beans in hot air. The first stage is at a temperature of not less than 332"C and the second stage at an equal or lesser temperature. The total flow rate of air is from 20 to 60 pounds of hot air for every pound of green coffee beans and roasting takes between one and a half and three minutes.

Known processes can be slow, polluting and very wasteful of hot air. Further, in the known processes the high volumes of hot air extract the aromas and other volatiles which are released from the beans during roasting. Frequently these are just squandered and released into the atmosphere leaving behind a coffee bean with comparatively little of its potential aroma and flavour content. Some coffee roasters have tried various means of capturing the aromas from the hot air in an attempt to add these later back to the coffee, but these have shown poor results.

It is an intention of the present invention to provide an improved process of preparing coffee beans in which at least some of the above-mentioned drawbacks are diminished or alleviated.

According to one aspect of the present invention there is provided a method of preparing coffee beans comprising the step of cooking the beans in oil.

The beans may be immersed in the oil at a temperature greater than 200-C, and preferably at about 240 C.

Preferably they are soaked in cold water for a time of up to 10 hours, before being cooked. After cooking the beans may be quickly quenched, preferably by the use of water.

Excess water and oil may be removed from the surface of the beans in a centrifuge.

The oil is preferably a vegetable oil such as peanut oil. The preferred temperature for the oil is within the range of between 235-C and 245it. Preferably the beans are cooked for from 60 to 90 seconds.

According to a second aspect of the present invention there is provided a method of preparing coffee beans, comprising soaking the beans in a predetermined amount of water prior to cooking them, said predetermined amount of water being chosen so that, at the end of the soaking process, substantially all the water has been soaked up by the beans.

Preferably the predetermined amount of water is approximately 23 parts by weight of water to 25 parts by weight of coffee beans. It is also preferred that the water should be hot water and also should be soft water.

The second aspect of the invention is not restricted to being used in conjunction with the first aspect of the invention. The method of the second aspect of the invention may be followed by conventional air roasting of the beans.

The present invention also provides coffee bean cooking apparatus for the cooking of the coffee beans, preferably comprising: means for cooking said beans in oil.

In this case the apparatus preferably further comprises means for quenching the cooked beans and/or means for removing surface oil from the quenched cooked beans, and/or means for transporting beans from the cooking means to the quenching means and from there to the removing means.

Additionally there may also be means for soaking the coffee beans in water, the transport means being adapted to transport the beans from said soaking means to said cooking means.

The hereinafter described method and apparatus provide advantages over the prior art for both aspects.

For example, there are considerable savings of energy compared to those of previous processes and further there is little or no pollution of the air or environment. So far as the coffee beans are concerned, it is possible to obtain an improved taste with less bitterness and to retain more flavour and aroma in the beans. Further, using the first aspect, the weight loss of the roasted beans can be reduced to between 2 to 5% from the level of 10 to 12% encountered in the prior art and more coffee solubles can be obtained per unit weight of coffee, e.g. 3.7g of roasted coffee per 100ml of coffee to drink, compared with between 5.7 and 8g per 100ml previously.The second aspect alone can provide improvements in yield and amount of solubles and further improve the results if used in combination with the first aspect, rather than with conventional air roasting.

The present invention is further described by way of non-limitative example with reference to the accompanying drawings, in which: Figure 1 is a block diagram for apparatus for use in a first embodiment of the present invention; and Figure 2 is a block diagram for apparatus for use in a second and third embodiment of the present invention.

A distinctive feature of the present invention is the cooking of green coffee beans in a medium of hot oil. This is equivalent to the roasting step found in the prior art.

In the first embodiment, of Figure 1, the green coffee beans are loaded into a cooking vessel 2 and cooked in vegetable oil at a temperature of approximately 2400C.

The coffee beans sink to the bottom of a heated oil vessel 2 and start to effervesce any air trapped within them.

Within approximately 25 to 35 seconds, depending upon the size and variety of beans, the water and other volatiles in individual cells of the beans are vaporised. The rigid cell walls at these high temperatures become soft and elasticated and expand with the internal pressures in the cells. The beans increase in size and float to the surface of the hot oil. At this stage the colour of the beans is pale brown.

Within another 30 to 40 seconds the beans "pop" and start to develop the distinctive coffee flavour and aroma.

The beans change their colour from pale brown to reddish brown. At this stage they are rapidly removed from the oil bath.

The excess oil which clings to the beans is shaken off in the excess oil removing means 4. The still hot beans are immediately plunged into a bath 6 of cold water at a temperature of from 5 to 100C. In doing this the hot beans implode with a slight loss of aroma. This occurs as the individual cells in the beans contract suddenly and the pressures of the hot internal steam and volatiles equalise.

The beans are left to cool in the water to the temperature of the water itself. This takes about 5 seconds. The plunging of the hot beans into the cold water instantly stops any uneven post-cooking of the bean by the residual heat of the bean which can be a problem in conventional roasters. A very fine layer of oil remains from the roasting process and this prevents the water from leaching any coffee solubles.

Finally, the cooled beans are centrifuged, for example in a continuous centrifuge 8 which removes traces of water and oil layers from around the beans.

In a second embodiment, shown in Figure 2, green coffee beans are soaked in a soaker 12 in hot water at about 95C before being cooked. They are kept in the water for about an hour. During this time the beans soak up the water and swell up slightly. Afterwards they are dried externally to remove the surface water. Then they are cooked and treated as mentioned above in respect of the first embodiment.

When soaking the beans, soft water is preferably used. The use of hard water increases cooking time later.

The water is absorbed or imbibed by the bean, hydrolyses the solubles within them, and softens the cell walls.

Soaked beans give a higher post cooking yield than nonsoaked beans.

When coffee beans are soaked in water caffeine and coffee solubles have a tendency to leak out of them when there is an excess of water. This is usually undesirable since it reduces the taste, aroma, yield and amount of solubles in the final product. In one aspect of the present invention a control for a limited amount of water is used so that all the water is soaked up into the coffee beans and no solubles are leaked out. In this way no useful aspect of the coffee is wasted. The solubles are retained and hydrolysed within the bean. For usual raw Arabica and Robusta coffee beans for example, the beans will soak up all water if water is provided in amounts of up to about 23 parts by weight water to 23 parts by weight coffee beans.Above this ratio of 23:25 by weight of coffee there is a tendency for some water not to be soaked up, and consequently for some solubles to leak out of the beans. Below that ratio the coffee is not being used to its full potential. This may, however, vary according to coffee types and conditions. For example, if the raw coffee is already overly dry to begin with it may soak up more water.

The time it takes for the water to be soaked up completely, depends not only on the amount of water but also on the temperature and pressure. At atmospheric pressure cold water in the 23:25 by weight ratio mentioned above may take up to 8 hours before it is absorbed completely. On the other hand the same amount of water may be soaked up in one hour if the temperature is kept at 95-C. This time is reduced further by using slightly higher temperatures and pressures. Care must be taken, however, not to go too far and to render the beans uncookable. Improved taste, aroma, yield and amounts of solubles are a result of the beans being soaked in the abovementioned manner. This is so for the cooking method which involves oil as mentioned above and the conventional methods in which beans are roasted. The oil cooking of beans produces the best results though.Also Robusta beans, which are generally considered to be inferior to the Arabica beans are improved by the soaking such that they are on a par for a taste with the Arabica beans.

25g of raw coffee beans which have soaked up 23g of water gave a coffee bean yield of 28g after oil cooking.

This represents a 12% increase in yield over the starting coffee amount. For the actual making of coffee to drink 2.8g of cooked coffee were required per 100ml of water for soaked beans compared with 3.7g for non-soaked oil cooked beans and 5.7g for non-soaked atmospherically roasted beans.

When presoaked beans are cooked in oil the heat volatises all the cell volatiles and the water vapour and they stretch the elasticated cell walls to a greater extent than before. Again the coffee beans expand, increasing their volume, rise to the surface of the oil and start to "pop". As before the beans start to develop an aroma and flavour, changing colour from pale brown to reddish brown.

The beans are then removed; excess oil is removed in means 4; they are plunged into a bath 6 of cold water and centrifuged in means 8. Because presoaked beans tend to clump together in hot oil vigorous circulation of the oil, especially in the lower part of the oil vessel should be maintained. This ensures more even cooking.

Rather than soak the green coffee beans for a short time, in a third embodiment the beans are soaked in excess cold water for about 9 hours in the soaker 12. By doing this the caffeine in the coffee beans is drawn out and dissolves into the water and the beans are left looking pale green and are decaffeinated. Again these beans have increased considerably in size and weight. They too are cooked at 240it as before. The decaffeinated beans increase in volume and float to the surface within about 25 seconds. They are, however, left longer to cook at the top of the oil as they take longer to develop the aroma, flavour and colour. They are removed after about 120 seconds. Excess oil is removed; the beans are quenched and the excess water and the final oil layers are removed.

Again the aroma, flavour and solubles yield of the decaffeinated coffee increases from the conventional process. However, the soaking process to remove caffeine does also remove other, not unwanted, solubles.

Popping is encouraged in the present invention since it allows the hydrolysing of the volatiles of the bean and gives greater access to the inside of the bean to the cooking oil.

Different types of beans take different lengths of time at different temperatures to cook, cool, soak up water etc. If the coffee is therefore to be blended, then the different varieties of green beans, in most cases, should be cooked before being blended.

In the above three embodiments the cooking oil is regenerated, that is it is removed from the cooking vessel 2 and cleaned in a filter 10 before being returned to the vessel 2 to be reused. The majority of what is obtained from filtering the oil is chaff from the beans. Further to the filter 10 the excess oil is washed off from the chaff with hot water and the chaff is centrifuged. The chaff has by then developed the coffee aroma and can be used by adding it to the roasted coffee beans to increase the aroma.

Other ways of regenerating the oil as well as or instead of filtering may be used.

The oil could be filtered not only from the cooking vessel but can also be collected for reuse from the oil removing means 4, and/or separated from the water and collected from the centrifuge means 8. The water too, in the various processes could be recycled.

Refined peanut oil may be used in the above process.

This oil is largely unaffected by the roasting process and does not become noticeably contaminated, other than by the build up of chaff which may be removed by the filtration step discussed above.

One of the reasons for the decrease in the bitterness of the coffee produced by the above discussed embodiments is because, by using hot oil, the bean do not become noticeably charred, and this includes the chaff. Charred chaff is one reason why coffee can be bitter. Because the ends of the bean, when growing, curl round almost to meet in the middle, the surface skin or chaff becomes trapped there and cannot usually be removed. This trapped chaff is susceptible to charring in conventional hot air roasting methods. In the above discussed embodiments even if the chaff cannot be removed from the centre it is not susceptible to charring and causing bitterness. Further the shape of the bean can lead to uneven roasting with hot air but the use of oil provides a more even cooking.

It has been found that the process does not work well below 200etc. It is slow and the resulting coffee is not much improved. The preferred temperature of the oil can be lowered from 2400C to about 220 C provided the ratio of oil to beans is sufficient and the circulation of oil within the vessel increases.

Vegetable oils are ideally suited for the cooking process, that is such vegetable oils as peanut oil, corn oil etc. In the described embodiments the preferred temperature of the peanut oil is 240it. The required cooking can occur at temperatures above this but the oil begins to smoke at such temperatures and without sufficient ventilation this can be unpleasant. In any case such oils as olive oil begin to smoke at about 150*C and it is therefore not a preferred oil. Whilst the coffee beans can be cooked at the higher temperatures in smoking oil there is a limit in terms of how quickly the beans can be processed and removed. As the temperature increases so the cooking time decreases. Also with higher temperatures, ultimately there will be uneven cooking of the beans.

A further consideration in the choice of oil is whether the oil taints the beans. Peanut oil does not noticeably provide any taste of its own to the beans; olive oil does. The choice of oil can also depend on how many times it can be reused before it has to be changed. In the case of peanut oil it can be reused back in the cooking vessel approximately 20 to 30 times at high temperatures.

The only treatment required to reuse the oil is filtering it for solids. In other oils, such as corn oil, the number of reuses tends to be lower, for example about 10.

If preferred the oil that is used may be a blend of various oils.

During cooking the coffee beans themselves reach a temperature in the range of from 210 to 220it. It is a temperature of at least about 205'C which is required for the telltale colour changes to occur.

The particular apparatus for use in the present invention may vary within the scope of the invention. For instance, the beans do not need to be immersed in a vessel of oil but may be cooked in a continual stream of oil either passing along the length of a bed or across its width or through its depth. Other means may be used for removing excess oil and water, such as bringing the beans into contact with an absorbent material, or using chemical means. Also cold air could replace cold water, etc.

Whilst only vegetable oils have been mentioned, mineral oils could be used, but might not be acceptable to some coffee drinkers.

Claims

1. A method of preparing coffee beans comprising the step of cooking said beans in oil.

2. A method according to claim 1, wherein said beans are immersed in said oil.

3. A method according to claim 1 or 2, wherein said oil is at a temperature of greater than or equal to 2000C.

4. A method according to claim 3, wherein said temperature is within the range from 220"C to 260"C.

5. A method according to claim 4 , wherein said temperature is within the range from 235it to 245eC.

6. A method according to any one of the preceding claims wherein said beans are cooked in said oil for a time within the range from 40 to 180 seconds.

7. A method according to claim 6, wherein said times are within the range of from 60 to 90 seconds.

8. A method according to claim 6, wherein said times are within the range from 100 to 140 seconds.

9. A method according to any one of the preceding claims wherein said oil comprises at least a majority of vegetable oil.

10. A method according to claim 9 wherein said vegetable oil comprises at least a majority of peanut oil.

11. A method according to any one of the preceding claims further comprising the step of quenching said beans after said cooking step.

12. A method according to claim 11 wherein water is used to quench said beans in said quenching step.

13. A method according to claim 11 or 12 wherein said quenching step is at a temperature in the range of from -5eC to 20or.

14. A method according to claim 13 wherein said quenching step is at a temperature in the range of from 0 C to 10 C.

15. A method according to any one of the preceding claims further comprising the step of removing excess surface matter from said beans after said cooking step.

16. A method according to claim 15 wherein said removing step comprises the step of centrifuging said beans to remove at least surface oil.

17. A method according to claim 15 or 16 when dependent upon any one of claims 11 to 14, wherein said removing step occurs after said quenching step.

18. A method according to any one of the preceding claims further comprising means for regenerating the cooking oil for reuse.

19. A method according to claim 18, wherein said regenerating means comprises filtering means.

20. A method according to any one of the preceding claims further comprising a step of soaking said beans in water prior to cooking them in oil.

21. A method according to claim 20, wherein said beans are soaked for a time of up to 2 hours.

22. A method according to claim 20, wherein said beans are soaked in excess water for a time of up to 10 hours.

23. A method of preparing coffee beans, comprising soaking the beans in a predetermined amount of water prior to cooking them, said predetermined amount of water being chosen so that, at the end of the soaking process, substantially all the water has been soaked up by the beans.

24. A method as claimed in claim 23, wherein the predetermined amount of water is up to approximately 23 parts by weight of water to 25 parts by weight of coffee beans.

25. A method according to claim 23 or 24, wherein the water in which the beans are soaked is at a temperature of more than 800C.

26. A method according to claim 25, wherein the water in which the beans are soaked is at a temperature of between 90 C and 100"C.

27. A method according to any one of claims 23 to 26, wherein the soaking is terminated once all of the soaking water has been soaked up by said beans.

28. A method according to any one of claims 23 to 27, wherein the soaking is continued for 2 hours or less.

29. A method according to any one of claims 23 to 28, wherein the water in which the beans are soaked is soft water.

30. A method of preparing coffee beans, wherein the beans are first soaked in accordance with the method of any of claims 23 to 29 and are subsequently treated in accordance with the method of any of claims 1 to 19.

31. A method of preparing blended coffee comprising the step of preparing coffee beans according to any one of the preceding claims, for two or more varieties of coffee beans and blending said prepared beans together after said cooking step.

32. Apparatus for cooking coffee beans according to a method in accordance with any one of claims 1 to 22 or claim 30.

33. A method of preparing coffee beans substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

34. Coffee bean cooking apparatus comprising: means for cooking said beans in oil.

35. Apparatus according to claim 34, further comprising means for quenching the temperature of said cooked beans.

36. Apparatus according to claim 35, further comprising means for removing surface oil from said quenched roasted beans.

37. Apparatus according to claim 35 or 36, further comprising means for transporting said beans from said cooking means to said quenching means.

38. Apparatus for preparing coffee beans substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.