GB1602709A - Method of fermenting tea - Google Patents

Description

(54) A METHOD OF FERMENTING TEA (71) We, JAMES FINLAY & COMPANY LIMITED, a British Company of P.O. Box 58, Finlay House, 10-14 West Nile Street, Glasgow G I 2PP, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: The present invention relates to a method of fermenting tea.

In the manufacture of black tea, withered green tea leaf is cut or rolled in order to damage the cells, and initiate the so-called process of fermentation, an enzymic process which depends on the presence of oxygen. When fermentation is considered to have proceeded sufficiently, enzymic activity is teminated by drying the leaf.

It is well known that the tempeature of the leaf during fermentation and the time for which fermentation is allowed to proceed are of critical importance in determining the character of the black tea produced. This character is described by tea tasters in a multitude of terms, but two terms commonly employed are 'brightness' and 'colour' and will be used illustratively herein.

'Brightness' describes the well known orange hues which are visible in tea liquor when consumed with milk, and which so easily differentiate the appearance of a cup of tea from that of a cup of coffee. 'Colour'. on the other hand, refers to the darker brown tones which are generally associated with a strong cup of tea.

Short fermentation times generally produce bright teas with little colour, whereas longer fermentation time increases colour, usually at the expense of brightness. A slight increase of leaf temperature during fermentation increases the speed of the chemical reactions which are occurring in the fermenting leaf, and consequently a given brightness or colour is reached more rapidly.

It is well known that tea produced at a higher leaf temperature for a shorter fermentation time is not identical to that produced at a lower temperature for a longer time. The effects of time and temperature are not therefore interchangeable, and the use of the correct temperature for the correct time is essential to good tea manufacture.

Unfortunately, leaf temperature is not easy to control and is one of the objects of the invention described herein.

Historically, the most common method of damaging withered tea leaf to induce fermentation was to roll the leaf, either by hand or on a mechanical rolling table, thus producing an open type of "dhool". As heat is generated by the process of fermentation, the "dhool" is spread in a thin layer on a floor in an attempt to maintain an even temperature throughout the leaf bed, and to permit air to come into contact with the leaf, thus providing the oxygen required for fermentation. More recently, continuous cutting processes have been introduced to replace rolling which is a batch operation. However, such cutting results in a more compact leaf mass which makes it even more difficult to maintain an even temperture throughout the bed and to ensure sufficient ingress of oxygen.Attempts have been made to resolve these problems by blowing air through the leaf (see, for example, Patent Specification No. 885,027) but this method is not entirely successful in contolling the temperature, and also results in the loss of volatile constituents from the leaf. As these constituents may significantly contribute to the characteristic black tea aroma, their loss is most undesirable.

The invention provides a method of fermenting tea. which method comprises introducing rolled or comminuted tea leaf into a trough having a shaft disposed longitudinally therein, the shaft having a plurality of paddles extending radially therefrom arranged in a helical configuration, maintaining the interior of the trough at a desired temperature suitable for the fermentation of tea, and rotating the shaft about its axis thereby causing the paddles to agitate and aerate the leaf tea and to convey the leaf tea from one end of the trough to the other.

The internal surface of the trough may be maintained at a constant temperature preferably by means of a jacket for the passage of a suitable fluid, e.g. a water jacket.

In carrying out the method of the invention a number of such troughs may be used in series, and the individual troughs may either be arranged in the same horizontal plane, or they may be disposed in a vertical array so that fermenting leaf discharged from one trough falls into the trough below it. Vertical arrangement is useful in making most economical use of limited floor space .

One of the troughs, usually the lowest, may be made longitudinally movable, so that the overall residence time of the leaf in the troughs may be adjusted by moving this trough longitudinally, the movement thus causing the leaf to fall into the trough part away along its length and thus reducing the leaf residence time in that trough.

When the troughs are arranged in a vertical array, it is not essential that the axes of all the troughs be in line, and troughs can, for example, be positioned at right angles to each other. Such a configuration may facilitate installation where limited space is available.

Use of more than one trough is, of course, not essential. One trough of sufficient length, may be adequate, suitable intermediate spider supports being used to carry the shaft, if necessary.

However, additional aeration of the fermenting leaf can be achieved as the leaf passes from one trough to the next by fitting a rapidly rotating paddle, which is referred to in the industry as a "ball breaker", below the outlet of the trough.

Two shafts, arranged for rotation in opposite directions may preferably be provided in the or each trough. The capacity of such double shaft units, because of the increased width thereof. is considerably greater than that of a single shaft unit, and economies are therefore achieved in construction costs and floor space.

An alternative way of varying the residence of time of the fermenting leaf is to adjust the angle of the paddles so that at a given speed of rotation, the residence time of the leaf may be increased by decreasing the angle of the paddles, and vice versa.

If the angle is made too small, difficulty is encountered at shut down in clearing the unit of fermenting leaf, the reason being that the leading edge of one paddle does not pick up leaf left behind by the trailing edge of the preceding paddle. This can be overcome by constructing the paddles so that part of the trailing edge is set at an angle to the remainder of the paddle to deflect the tea into the path of the next paddle. Thus, for example a small "tail" may be fitted at an angle of 130 to the trailing edge of each paddle. The tails have little effect on the residence time when the unit is full of leaf, but when the leaf level is low at the end of operation, the tails push leaf into the path of the following paddle, thus facilitating rapid elimination of leaf from the unit.

Control of the speed of rotation of the shaft may be achieved electrically by electronic control of the motor speed, or mechanically by means of a suitable variable speed V belt drive or variable speed gear unit, or by any other suitable means.

When variable speed control is used, clearance of leaf from the unit at shutdown is facilitated by increasing the speed of rotation at that time.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings in which Figure 1 is a schematic view of apparatus according to the invention, employing three fermentation units, the bottom one of which is longitudinally movable Figure 2 is a plan view of a doubleshaft-type unit according to the invention Figure 3 is a front elevation of the unit of Figure 2, and Figure 4 is a section on A-A in Figure 3.

Figures 5 and 6 are respectively an elevation and plan view of paddles which form part of the unit of Figures 2 to 4, Figure 7 is a front elevation of a specific embodiment arrangement according to the scheme of Figure 1, using three units as shown in Figures 2 to 4, and Figure 8 is an end elevation of the apparatus shown in Figure 7.

Referring first to Figure 1, troughs A and B are fixed, and unfermented rolled or comminuted green tea leaf is supplied to trough A, by means of leaf feed conveyor 10.

Trough C is longitudinally movable between positions C1 and C2 to give,respectively the minimum and maximum possible overall residence times for the leaf. Any intermediate position may be chosen, depending on the degree of fermentation required. The fermented leaf is discharged through outlet 11 onto discharge conveyor 12.

The twin unit of Figures 2 to 4 comprises a trough 1, containing two shafts 2 each having a plurality of projecting paddles 13. The shafts 2 are journalled in bearings 3.

In Figure 7, four shafts of two vertically stacked troughs are driven from a single variable speed drive 4, and reduction gear 5, by means of sprockets 6 and a chain 14. The two shafts of a third trough 7 are driven from a separate variable speed drive 8. During the period in which the leaf is held in each trough, its temperature is controlled by circulation of water from a temperature controlled reservoir, through a sectioned jacket 9 attached to the lower surface of the tough. Continuous aeration of the fermenting leaf results from agitation caused by the paddles, but to ensure proper agitation and avoid packing of leaf in the space between paddles it has been found that in the embodiment specifically described, the pitch of the helix defined by the paddles should not be less than the radius of the paddles.

The invention is illustrated by the following example: The apparatus used comprised three stainless steel double shaft fermenting troughs located one above the other, the lowest trough being movable and mounted on rails. The length of each trough was 10 ft., and the diameter of each paddle and shaft assembly section 18". The vertical walls of each trough extended 15" above the shafts. The shell of each trough was jacketed, and water at a preselected temperature was continuously circulated through each jacket. The maximum working volume of each trough to the top of the paddles was 40 cu. ft., and the density of cut leaf is 17.5 kg/cu.ft. The maximum capacity of each unit was therefore 700 kg. of fermenting leaf. For a fermentation time of 2 hours with a cut leaf feed of 900 kg/hr., a residence volume of 1800 kg. of cut leaf was required.As the first and second troughs contributed 1400 kg. capacity, a capacity of 400 kg was required for the third trough. The third trough was therefore moved so that approximately two thirds of its length was utilized. In order to facilitate this location, a calibration scale was marked along the length of the third trough, and movement achieved by means of a simple cable winch. Water at 270C was circulated through the jacket on the first trough, and at 24"C through the jackets of the second and third troughs. Measurement of the leaf temperature with an electronic thermometer indicated that the bulk of the leaf was substantially at the temperature of the jacket water in each trough.

On discharge from the third trough, the fermented leaf fell on to a conveyor and was dried in a conventional tea dryer. When the resultant black tea was compared by tea tasters with black tea produced by the conventional tea fermentation processes it was generally judged to be superior in brightness, strength and aroma.

WHAT WE CLAIM IS:- l. A method of fermenting tea, which method comprises introducing rolled or comminuted leaf tea into a trough having a shaft disposed longitudinally therein, the shaft having a plurality of paddles extending radially therefrom arranged in a helical configuration, maintaining the interior of the trough at a desired temperature suitable for the fermentation of tea, and rotating the shaft about its axis thereby causing the paddles to agitate and aerate the leaf tea and to convey the leaf tea from one end of the trough to the other.

2. A method as claimed in claim 1, wherein the interior of the trough is maintained at a constant temperature by a temperature control means.

3. A method as claimed in claim 2, wherein the temperature control means is a water jacket.

4. A method as claimed in any one of the preceding claims, wherein the trough is provided with at least two of the said shaft and paddle assemblies disposed longitudinally therein, the shafts being arranged for rotation in opposite directions.

5. A method as claimed in any one of the preceding claims wherein the speed of rotation of the or each shaft is variable.

6. A method as claimed in any one of the preceding claims wherein the angle of the paddle is variable.

7. A method as claimed in any one of claims 1 to 5, wherein the pitch of the helix defined by the paddles is fixed and at least equal to the radius of the paddles.

8. A method as claimed in any one of the preceding claims wherein the trailing edge of each paddle is set at an angle to the remainder of the paddles.

9. A method as claimed in one of the preceding claims wherein the tea, is conveyed through a plurality of the troughs arranged in series.

10. A method as claimed in claim 9 wherein the troughs are disposed in a vertical array and each trough except the bottom trough is arranged so that the partially fermented tea is discharged into the trough immediately below.

11. A method as claimed in claim 10 wherein one of the troughs is longitudinally movable and the tea is conveyed along only a portion of the length thereof.

12. A method as claimed in any one of claims 9 to 11 wherein the tea is conveyed through a rotatable paddle between any two successive troughs.

13. A method of fermenting tea substantially as hereinbefore described with reference to the accompanying drawings.

14. Fermented tea when produced by a method as claimed in any one of the preceding

Claims (1)

1. claims.