GB2043523A - Pelletising infusion material - Google Patents

Abstract

Infusion material, such as fired leaf tea, is prepared for storage and/or transport by being pelleted using a roller and ring extrusion press. The pelleted material can be stored for long periods without suffering undue spoilage through the growth of bacteria and moulds, and its increased bulk density facilitates transport. In the case of leaf tea, the pellets can be crushed to yield material suitable for use in tea bags or in the manufacture of instant tea. The leaf tea has a moisture content of at least 10%, and preferably not greater than 15% prior to extrusion. The extrusion head and/or the emergent pellets, are cooled.

Description

SPECIFICATION Handling of material The present invention relates to the handling of material, such as leaf tea, in bulk for the purposes of storage and transport.

The manufacture of tea products often involves the transport of huge quantities of the raw material (fired leaf tea) from the tea-growing areas of the world to processing factories which are geographically remote from the tea plantations. For example, leaf tea is dispatched from plantations in India, Sri Lanka, Africa and South America for further processing in factories in Western Europe and North America. Although the tea is transported in the fired state, i.e. it has been heated and dried to destroy the natural tea enzymes in the leaf in order to prevent continued fermentation of the leaf, it is still a relatively delicate commodity. The flavour of the final beverage produced from the tea can be affected adversely by spoilage resulting from bacterial or atmospheric contamination while the fired leaf tea is being stored and transported over such vast distances.Traditionally, leaf tea is transported in the familiar wooden tes chests lined with metal to prevent such contamination. Nowadays the metal lining is usually aluminium foil, although formerly it was lead sheet. This method of transport is becoming increasingly uneconomic because not only are the tea chests expensive to manufacture, but also the tea in the form of loose leaves is inevitably of low bulk ensity and hence occupies an unduly large volume.

Clearly the volume occupied by the leaf tea could be reduced if the leaves are compacted together. Historically, when tea was a product known only in the eastern world, it was transported within that area in the form of "tea bricks", ie small blocks of compacted leaves.

Such tea bricks could be readily transported on the backs of camels and other beasts of burden, and for use in producing beverages were broken up by hand. Although in principle such a method could be used today to transport the vast quantities of tea now being conveyed across the world, the expenditure required in equipment and energy necessary to produce large quantities of individual tea bricks would be quite unacceptable.

It is also becoming common practice for tea to be processed in the country of origin, especially in the manufacture of so-called "instant tea '. Even though no transporting of the tea prior to processing may be involved, it can be necessary for the tea to be stored for some considerable period before being processed. In the tea-growing areas of the world the local climatic conditions necessarily include temperatures and humidities which render such storage difficult.

The invention therefore seeks to provide a method of handling leaf tea and similar infusion materials whereby the risk of spoilage during storage and transport may be reduced and the storage and/or transport of the leaf tea or other infusion material may be rendered more convenient or economic.

By the invention we have found that fired leaf tea can be successful pelleted using the types of extruders and ring-roll presses commonly employed to produce animal feedstuffs in hard compact free-flowing form. Similarly, pelleting can be applied to other types of soft plant material from which aqueous infusions of beverage quality can be prepared. Generally such other types of plant material are of a herbal character.

In this specification the expression "infusion material" is used to mean any soft plant material such as leaves (which in practice can comprise a proportion of stems and/or shoots in addition to a predominate leaf content), petals and flowers in general, from which an aqueous beverage can be prepared. The infusion material in most common use is derived from the tea plant, Camellia sinesis, (L) O. Kuntze. Depending on the extent to which fermentation of the leaf tea after picking, cause by the natural enzymes in the leaf, has been allowed to continue prior to firing, the leaf tea can be green, black or oolong.A wide variety of other soft plant materials, derived for example for mats6, chamomile, mile, vervien, linden, hibiscus, orange blossom, lemon grass, blackberry leaves, skullcap, verbena, camfrey and alfalfa, are used in various parts of the world in the preparation of infusions consumed as beverages for refreshment or medicinal purposes.

The invention therefore firstly provides a method of preparing infusion material for storage and/or transport, in which method the infusion material is expressed through a die and the expressed material is sub-divided into pellets.

The invention further provides a method of handling infusion material, in which method the infusion material is stored in the form of pellets made by extrusion.

The invention also provides a method of handling infusion material, in which method the infusion material, in the form of pellets made by extrusion, is transported to a processing factory, and the pellets are crushed at the processing factory to yield finely-divided infusion material.

In the remainder of this specification the invention will be described in relation to the handling of fired leaf tea. The applicability of the invention to the handling of other types of infusion materials will be readily apparent to the skilled reader.

The most preferred types of pelleting equipment for use in the process of the invention is a ring-roll press. In order to minimise any loss of tea quality during the pelleting operation, the use of a pelleter having a chilled extrusion head is preferred.

Alternatively, or in addition, the pellets should preferably be chilled by an impinging current of cold air, or by transfer to a cold environment such as a cold store, immediately following extrusion. These procedures can help to reduce any possible loss of volatile flavour components.

Usually a pellet from a ring-roll press is basically cylindrical in shape, and typically has a diameter of from 5 to 1 5 mm and a length of from 10 to 30 mm, and a specific gravity in excess of 1.

To facilitate the production of robust pellets in accordance with the invention, it is desirable that immediately prior to pelleting the moisture content of the fired leaf tea should be at least about 10% by weight. In general, it is not necessary for the moisture content of the fired leaf tea to be greater than about 15% by weight immediately prior to pelleting, and in fact for preservation reasons a moisture content much in excess of 15% can be undesirable. The normal moisture content of freshly fired leaf tea is usually about 3 to 4% by weight.However, freshly fired leaf tea can rapidly pick up additional moisture from the atmosphere and the typical moisture content of the fired leaf tea of commerce which has been stored and/or transported by traditional methods is generally in the range of about 7 to 10% by weight. The moisture content of any given sample of fired leaf tea will depend on the processing, handling and prevailing climatic conditions to which it has been exposed. In any event, it is envisaged that in most instances it will be necessary to add moisture to the fired leaf tea in order to bring it into the optimum range for pelleting. Such addition of moisture can be achieved readily by, for example, spraying an appropriate quantity of water onto the leaf tea while the leaf tea is being agitated in a mixer.In an alternative procedure however, it may be preferable to modify the firing and drying conditions of the conventional tea process in order to leave a higher moisture content in the freshly fired leaf so that it is immediately suitable for pelleting.

During the pelleting operation some of the moisture present in the fired leaf tea can be expressed from the tea or lost by evaporation. Desirably, the final moisture content of the pelleted leaf tea will not exceed about 12% by weight, otherwise superficial spoilage through bacteria and mould growth may occur during storage and/or transport.

When applied to the transport of leaf tea, this technique has the dual advantages of dramatically increasing the bulk density of the tea and thus reducing its storage and transport costs, and due to the hard compact nature of the individual pellets much of the leaf tea within each individual pellet is inherently protected against contamination during storage and transport.

On arrival at a tea processing factory, the pellets can be readily broken up using conventional milling/crushing equipment to regenerate the tea in the form of very finely divided particles or flakes. The process of the invention is thus clearly not suitable for tea which is intended to be sold as loose leaf tea. However, at the present time much beverage tea is sold in the form of tea bags, in which the leaf tea must be in a very finely divided form in order to yield a satisfactory infusion. Further, much tea is now converted to so-called "instant tea" in a process which typically involves making an aqueous extract of the leaf tea, separating the insoluble material, and drying the extract to collect the water-soluble tea solid.Any such extraction process can only proceed efficiently if the leaf tea is very finely divided prior to infusion, and leaf tea which has been stored or transported in accordance with the invention is eminently suitable.

A surprising feature of the invention is that while it would be expected that the severe conditions of temperature and pressure associated with pelleting operations would be too harsh to apply to such a delicate commodity as leaf tea, we have found instead that the beverage quality of at least the cheaper grades of fired leaf tea which have been pelleted, stored and milled in accordance with the invention is not significantly inferior to that of leaf tea of comparable grade which has been stored loose in tea chests in the convention manner and then milled to produce finely divided leaf tea for tea bag or instant tea use.

The tea pellets of the invention can be transported in traditional tea chests. Alternatively, in view of the inherent protective nature of the individual pellets, the tea can be transported in a much larger bulk container, and the concept of such pelleted leaf tea being loaded directly into the holds of ships is a distinct possibility. In such a procedure, the free-flowing robust nature of the pellets would enable bulk loading and unloading equipment to be used, such as is already employed in the handling of grain and finely divided mineral commodities.

It will be appreciated that although the tea pellets will make up a load of substantially higher density than will loose leaf tea, there will be voids left in between the individual pellets. Where the pelleted tea is conveyed in tea chests or other handleable bulk containers, such voids could be filled by packing the pellets together with unpelleted leaf tea which on arrival at a processing factory can be separated if desired from the pellets by, for example, sieving before the pellets are crushed or milled.

The following Examples illustrate the invention iin greater detail.

Example I Three batches of a commercial grade of fired black leaf tea ("Lubona"), having an original moisture content of 8.7% by weight, were moistened by the addition of various levels of water by spraying onto the leaf tea churning in a bowl mixer. The three moistened batches were pelleted using a standard Buhler animal feedstuff ring-roll press at a through-put in the range 0.6 to 1 kg/min. The pellets so formed were cylindrical and had an approximate diameter of 10 mm and a typical length of about 25 mm. The pellets emerged from the press at a temperature of 25'C. The pellets so formed had final moisture levels as follows: Percent water Moisture prior Final Batch added to pelleting Moisture percent A 1 9.7 B 2 10.7 9.7 C 3 11.7 11.0 The material of Batch A lead to sever dusting in the press, and the pellets that emerged crumbled easily.This run was discontinued. This implies that a moisture content prior to pelleting of at least about 10% is desirable.

The pellets of Batches B and C were robust, and had an approximate density when loosely packed of 666 g/litre and 625 g/litre respectively, compared to an approximate density of 220 g/litre for the loosely packed commercial leaf tea.

Samples of pellets from Batches B and C, plus a sample of the original leaf, were stored for two weeks under "tropical" conditions (30"C/90%RH). Whereas the leaf tea had developed a significant population of aerobic bacteria and a visible mould growth, the pelleted tea was bacteriologically completely safe at the end of the storage trial.

Sample After 2 weeks under tropical conditions: Aerobes Moulds Unpelleted leaf 44.0 X 103 1.6 > < X 106 106 Batch B pellets 1.5 X 10' Indeterminable Batch C pellets 1.2 x 102 2.0 X 101 Further samples of both batches were crushed in a standard domestic food blender, producing a powdered mass of leaf tea which passed through a 1 700 micron screen. The hot waterextractable solids were determined using a standard method, and compared in quantity to the solids extractable under strictly comparable conditions from the original fired leaf tea milled to the same particle size.The following results were obtained: Sample Percentage extractable in hot water Original leaf 40.4 Batch B pellets 41.5 Batch C pellets 40.8 The variation in the percentages recorded is within experimental error, and it is clear that the process of the invention does not impair the quantity of solids extractable from the leaf tea.

Example 2 Three batches of a commercial grade of fired black leaf tea ("Lubona", having an original moisture content of 9.5% by weight, were moistened by the addition of various levels of water in the manner used in Example 1. The batches of leaf tea were then pelleted using a standard Buhler animal feedstuff ring-roll press, operated under conditions similar to those used in Example 1, yielding cylindrical pellets of approximate diameter 1 Omm and about 25mm in length. The levels of water added to the leaf tea, and the final moisture contents of the pellets, are given below: Percent water Moisture prior Final Batch added to pelleting moisture percent D 2.5 12 9.7 E 5 14.5 12.0 F 10 19.5 16.1 Each formed robust pellets, but those of Batch F developed an obvious mould growth after only a few weeks storage.A final moisture level os 12% (Batch E) is probably the maximum that can be tolerated from this point of view. This suggests that a moisture content immediately prior to pelleting of about 15% by weight is a desirable maximum.

Example 3 Two batches of pelleted commercial "Lubona" blend black leaf tea were prepared, using the procedure of Example 1, water being added as follows: Percent water Batch added G 2 H 3 A sample of each batch was stored for two years in an open-topped container under ambient conditions in Southern England. For comparison purposes, a sample of the unpelleted tea blend, with no added water, was stored under identical conditions for the same period. After two years each sample was subjected to a standard bacteriological analysis, with the following results: Sample After two years under ambient UK conditions Aerobes Moulds Unpelleted leaf 1.2 X 105 6.1 X 104 Batch G 3 X 102 Indeterminable Batch H 1 X 103 Indeterminable These results further illustrate the benefits of the invention in preventing unacceptable spoilage of leaf tea during prolonged storage.

Claims (10)

1. A method of preparing infusion material for storage and/or transport, wherein infusion material is expressed through a die and the expressed material is sub-divided into pellets.

2. A method according to claim 1, wherein the pelleting of the infusion material is effected by means of a ring-roll press.

3. A method according to claim 2, wherein the infusion material is fired leaf tea.

4. A method according to claim 3, wherein the moisture content of the fired leaf tea immediately prior to pelleting is at least about 10% by weight but not greater than about 15% by weight.

5. A method according to claim 1 and substantially as hereinbefore described with reference to any one of the Examples.

6. A method of handling infusion material, wherein the infusion material is stored in the form of pellets made by extrusion.

7. A method of handling infusion material, wherein the infusion material, in the form of pellets made by extrusion, is transported to a processing factory, and the pellets are crushed at the processing factory to yield finely-divided infusion material.

8. A method according to claim 6 and claim 7 wherein the infusion material is fired leaf tea.

9. Fired leaf tea in the ,orm of pellets made by extrusion.

10. Fired leaf tea in the form of pellets which are basically cylindrical in shape and which have a diameter of from 5 to 1 5 mm, a length of from 10 to 30 mm, and a specific gravity in excess of 1.