GB2208096A

GB2208096A - A process for the preparation of vegetable material having improved extractability

Info

Publication number: GB2208096A
Application number: GB8815728A
Authority: GB
Inventors: Antonius Petrus Gijsbe Leemans
Original assignee: Douwe Egberts Koninklijke Tabaksfabriek Koffiebranderijen Theehandel NV
Current assignee: Douwe Egberts Koninklijke Tabaksfabriek Koffiebranderijen Theehandel NV
Priority date: 1987-07-03
Filing date: 1988-07-01
Publication date: 1989-03-01
Anticipated expiration: 2008-07-01
Also published as: GB2208096B; GB8815728D0; NL8701569A

Abstract

A process for preparing vegetable cell material having improved extractability comprises moistening vegetable cell material with water or an aqueous solution, reducing the pressure, and subsequently drying the moistened vegetable cell material. The product so obtained may be dissolved at from 0 to 25 DEG C or at from 70 to 100 DEG C. The vegetable cell material may be tea leaves, coffee (preferably ground coffee) or herbs.

Description

DESCRIPTION A PROCESS FOR THE PREPARATION OF VEGETABLE MATERIAL HAVING IMPROVED EXTRACTABILITY The present invention relates to a process for the preparation of vegetable cell material having improved extractability, to vegetable cell material obtained by said process, and to a method of preparing an extract from a vegetable cell material.

For a long time now, there has been a need for methods of preparing drinks from vegetable cell materials, such as coffee, tea and/or herbs by extraction with cold water.

In addition, there is a need for shortening the extraction time, in particular for use in automatic dispensing machines, in which fresh coffee or fresh tea is prepared starting from ground coffee or tea leaves, rather than powder or a concentrated extract. An improvement of the extractability with cold water is of importance in particular for tea leaves, as tea leaves of improved extractability can be used for making iced tea without much trouble. In fact, normal tea leaves require time-consuming operations, such as, for example, cooling the extract, or first making a concentrated hot extract, which is subsequently diluted with iced water to the required strength.

The improved extractability of cell material also has advantages in using the cell material in beverage dispensing machines. In particular machines for dispensing freshly-made tea use a relatively large amount of tea leaves, compared with the ultimately obtained strength of the product, because owing to the available short extraction time, only a portion of the tea dry solids present can be extracted.

In EP- A- 0 135 222, it is described that black tea can be treated with tannase and one or more cell wall degrading enzymes. After extraction and drying, this gives an instant tea which is better soluble in cold water. This process has the disadvantage, however, of requiring a special enzymatic pretreatment of the tea, while the enzymes used should subsequently be deactivated with a base, followed by heating.

EP- A- 0 209 937 describes a process in which tea leaves are first soaked with a small amount of hot water, followed by extraction with cold water. Although that process is a clear advance for the production of iced tea, it still does not permit treating vegetable cell material with it in a simple manner, which material can subsequently be marketed, for example, in bags of wet-strength paper.

It has now been found possible to provide a process for treating vegetable cellular material for improving its extractability, which comprises moistening vegetable cell material with water or an aqueous solution, reducing the pressure and subsequently drying the moistened vegetable cell material.

It has surprisingly been found that this process can be used for treating vegetable cellular material, such as, for example, tea leaves, coffee (preferably ground coffee) and herbs, whereby clearly improved extractability is obtained. This concerns both the extractability with water, in particular in the direction towards a better extraction of the dry solids, i.e., that a higher dry-solids content is obtained, and with hot water, in particular to the effect of reaching the desired degree of extraction more quickly. This latter is of course especially of advantage for application in beverage dispensing machines, in which it has hitherto been necessary to use a two-fold to three-fold excess of, for example tea leaves to obtain sufficient strength.

In the practice of the process, in principle, the vegetable cellular material is first moistened with water or an aqueous solution in a proportion of, preferably, 0.5 to 3 times the weight of the vegetable cellular material, more specifically 1.0 to 2.5 times. The pressure may vary within wide limits, but during moistening the pressure must not be too low, because the second stage of the treatment requires a minimum pressure drop. Preferably, the pressure during moistening is 0.8 to 5 bar. The period of moistening is not critical, but it should be taken into account that the cellular material must be able to absorb the moisture at least in part, while on the other hand it must be avoided, in particular when using large amounts of water, that there is too much extraction.The temperature of the water is not so essential either, but naturally the use of hot water leads to more rapid moistening than the use of cold water. The temperature of the water or the aqueous solution is therefore preferably from 0 to 100or, specifically from 10 to 40 C.

In addition to water, the moistening liquid may contain food-grade acids, salts, flavours or taste imparting substances, or mixtures of two or more of these substances. Examples are tea flavours, such as, for example, essential oils and the like, sweeteners, citric acid, and the like.

In the second stage of the treatment, which may take place in the same or in a different space, the pressure is reduced, preferably as quickly as possible, which results in rapid evaporation of the liquid. Naturally, this is accompanied by loss of heat.

This evaporation gives rise to boiling phenomena.

The degree of pressure reduction is determined, among other factors, by the initial pressure used, the quantity of water, and the temperature. The final pressure in this phase is preferably from 0.005 to 1 bar, and the ratio hetween the initial pressure and the reduced pressure is preferably no less than 3, and most preferably no less than 10. The upper limit of the ratio of the pressures is not critical and may range, for example, from 100 to 1000.

Subsequently, the vegetable material is dried to the desired final moisture content. This final moisture content varies depending on the nature of the material.

For tea, for example, it ranges from 1 to 10% by weight, and for coffee this value ranges from 1 to 8g by weight.

Drying can be effected in various ways. The cell material may be dried at atmospheric pressure by adding heat. Preferably, however, the material is dried at subatmospheric pressure, as this results in better extractability.

As, during drying in vacuo, heat is withdrawn from the material, this method can, in turn, be carried out in various ways. In fact, the conditions,pressure and heat supplied, can be selected so that no freezing of the moisture in the cell material occurs.Another possibility, which is preferred, is that the conditions are chosen so that freezing occurs. This, in fact, comes down to freeze drying. The advantage of this preferred process is that optimum extractability of the material is obtained.

This is particularly surprising, because a process in which the moistened material is first frozen and then freeze dried has considerably less effect on the rate of extraction.

The process which accordingly is most preferred comprises of moistening the vegetable cell material with water or an aqueous solution at normal pressure, followed by pressure reduction to about 0,01 bar (generally 0.005 to 0.1 bar). At this pressure, boiling effects are obtained first and subsequently the moisture is frozen. By controlled heat supply, sublimation takes place, which is allowed to continue until the desired final moisture content is reached.

The invention also relates to vegetable cell material having improved extractability, producible by using the process according to the invention. The invention also relates to a bag of wet-strength paper containing the vegetable cellular material obtained using the invention.

In a final aspect, the invention also relates to a method of preparing an extract from a vegetable cellular material, which comprises extracting a vegetable cellular material obtained by using the process according to the invention with water or an aqueous solution.

Depending on the desired temperature of the extract, the extraction can be carried out with a liquid having a temperature basically ranging from the freezing point to the boiling point of the liquid. For a cold drink, for example, for iced tea, the temperature of the extraction liquid is preferably chosen as low as possible, preferably from 0 to 250C. For making a hot drink, for example, in a tea dispensing machine, the temperature is preferably selected as high as possible, preferably from 70 to 1000C.

The invention is illustrated in and by the following examples, which are intended to illustrate the invention, but should not be construed to limit the invention in any way.

Six experiments were carried out, in each of which 700 g black Kenya tea was moistened under atmospheric pressure with water in various water-to-tea ratios (W/T ratio). In the comparative example, the tea was not moistened.

The five samples of moistened tea were subsequently subjected to vacuum (0.01 bar) and at that pressure freeze dried to a moisture content of 4% by weight.

Of the six tea samples, subsequently 2 g was extracted with 100 ml water of 10 C. The progress of the extraction was followed by determining the drysolids content in the extract.

The following table includes these data. The extraction efficiency relates to the amount of dry solids extracted from the tea, relative to the original quantity of tea. In this case: Dry solids in extract (g) x x 100% 2 (g) = extraction efficiency For comparison, a tea sample was moistened with water, frozen and freeze dried. The data are included as Comparative Example 2.

The results from the Table are shown graphically in the accompanying figure.

Table Example 1* I II III IV V 2* Extraction time Extraction efficiency (%) (min) 1 3 5 11.5 15 15 13 5 2.5 4.5 11 17.5 22 19 14.5 13.9 5 7.5 18.5 22.5 28 22 18.5 17.8 15 19.5 25 26 31 28 21.5 23.2 W/T ratio 0 0.5 1.5 2 2.5 3 2.5 *Comparative Example

Claims

1. A process for preparing vegetable cell material having improved extractability which comprises moistening vegetable cell material with water or an aqueous solution, reducing the pressure, and subsequently drying the moistened vegetable cell material.

2. A process as claimed in claim 1, in which the vegetable cell material is moistened at a pressure of from 0.8 to 5 bar and the pressure reduced to from 0.005 to 1 bar, with the ratio between the pressures being at least 3.

3. A process as claimed in claim 1 or 2, in which the amount of water or aqueous solution used for moistening the vegetable cell material is from 0.5 to 3.0 times the weight of vegetable cell material.

4. A process as claimed in claim 3, in which the quantity of water or aqueous solution is from 1.0 to- 2.5 times the weight of vegetable cell material.

5. A process as claimed in any of claims 1 to 4, in which the vegetable cell material is tea.

6. A process as claimed in any of claims 1 to 5, in which the vegetable cell material is dried at a pressure of less than 1 bar.

7. A process as claimed in claim 6, in which the pressure is selected so that the temperature of the cell material is below the freezing point of the liquid present in the cell material.

8. A process as claimed in claim 7, in which sufficient heat is supplied during the drying process that water can sublime.

9. A process as claimed in any of claims 1 to 8, in which the cell material is moistened at a temperature of from 0 to 1000C.

10. A process as claimed in claim 9, in which the cell material is moistened at a temperature of from 10 to 400C.

11. A process as claimed in any of claims 1 to 10, in which the aqueous solution contains food-grade acids, salts, flavours, taste imparting substances or mixtures of two or more of these substances.

12. A process for preparing vegetable cell material substantially as hereinbefore particularly described.

13. Vegetable cell material having improved extractability, whenever obtained by a process as claimed in any of claims 1 to 12.

14. A bag of wet-strength paper containing vegetable cell material as claimed in claim 13.

15. A method of preparing an aqueous extract of a vegetable cell material, which comprises extracting vegetable cell material obtained by using the process as claimed in any of claims 1 to 12 with water or an aqueous solution.

16. A method as claimed in claim 15, in which the temperature of the water or the aqueous solution ranges from 0 to 25 0C or from 70 to 1000C.

17. A method of preparing an aqueous extract of a vegetable cell material substantially as hereinbefore particularly described.