WO2000004788A1

WO2000004788A1 - Method for producing tea in particulate or leaf form with reduced labor and plant costs

Info

Publication number: WO2000004788A1
Application number: PCT/EP1999/005135
Authority: WO
Inventors: Giuseppe Imo Manzolli
Original assignee: Marlegreen Holding S.A.
Priority date: 1998-07-24
Filing date: 1999-07-19
Publication date: 2000-02-03
Also published as: AU5161499A; ITMI981729A1; IT1301871B1; ITMI981729A0

Abstract

A method for the production of tea in particulate or leaf form, comprising a step of harvesting the parts of the tea plant to be treated, characterized in that it comprises a step of freezing the parts of the tea plant at a temperature which is substantially between -40 °C and -150 °C to cause the rupture of their cell walls and of the sub-cell organelles due to the freezing of the protoplasm, and thawing step of causing a mixing of the oxidases and substrates which escape from the sub-cell organelles which are ruptured by the freezing step; after the freezing step and before the thawing step the parts of the plant are subjected to a mechanical action to detach the leaves from the remaining parts of the plant that are subjected to treatment. Said parts of the plant are then subjected to separation into the various elements that compose them.

Description

METHOD FOR PRODUCING TEA IN PARTICULATE OR LEAF FORM WITH REDUCED LABOR AND PLANT COSTS Technical field

The present invention relates to a method for producing tea in particulate or leaf form, with reduced labor and plant costs. Background art

Tea is a key beverage worldwide, since according to current statistics it is one of the most widespread and demand for it increases continuously, to the point of being consumed daily all over the world in its various commercial forms.

Tea is obtained by infusion of leaves, generally the first three, of the bud of the tea plant; these leaves contain a higher concentration, with respect to older leaves, of valued substances such as caffeine (theine) and catechins, which as a consequence of the particular processing to which the leaves are subjected give the infusion its typical aroma. The concentration of these substances decreases as the age of the leaf increases; accordingly, teas having a higher percentage of young leaves are more valued in terms of quality.

Although over three thousand different qualities of tea are commercially available, it is possible to divide tea production into three main qualities: black (fermented) tea, which is by far the most commercially widespread variety; green (unfermented) tea; and the so-called "oolong" (semifermented) quality. Flavored teas are also available next to these three main qualities. For the sake of simplicity in presentation, reference is made herein only to the production methods of black tea and green tea, since oolong teas are fermented, albeit to a lesser extent than black teas, and therefore their production method is very similar to the production method of black teas.

The classic production method for black teas and oolong teas begins with the harvesting of the buds, which is traditionally performed manually and is limited to the first three leaves of the buds. Harvesting is followed by a withering step, which is meant to reduce the humidity of the buds by 30- 50%, making the buds less brittle but pliable and free from nervure and therefore ready for the next treatment step. The subsequent treatment step, known as rolling, consists in rolling the leaves in different manners so as to rupture the cells and sub-cells walls of the leaves in order to release the substances contained therein, which are decisive in obtaining the characteristic aroma of the infusion. The so-called fermentation in tea production consists, more exactly, in an oxidation of the catechins produced, in the presence of oxygen, by the contact of these substances with enzymes (oxidases) contained in the leaves. Rolling, by rupturing the cell and sub-cells membranes, is indeed meant to produce contact of the oxidases with the catechins in the tissues, where a certain amount of oxygen is always present. The catechins, by making contact with the oxidases, are first transformed into orthoquinones and then into theaflavins and thearubigins, which give black tea its particular aroma, which is more or less strong depending on the intensity of the fermentations or oxidations, which depend on the reaction time, on the temperature and on the concentrations. After rolling, the tea leaves are left to rest for a preset time, so as to allow the development of the oxidation or fermentation, and they are then subjected to drying so as to reduce their humidity to approximately 5%, which is ideal as regards preservation (since higher humidities would entail the risk of causing the product to form mold, making it unusable) and as regards the aroma. Higher drying would in fact cause the tea to be scarcely fragrant in taste, since it would cause part of the substances that must enter the infusion to become insoluble or would in any case alter their taste, since in order to reach such levels of drying it would be necessary to bring the leaves to temperatures above 80°C, which are detrimental for these purposes. The production of green tea is different from the production of black and oolong tea mainly because the oxidation of the catechins is inhibited in the production of green tea. In this type of processing, the tea leaves, after harvesting, are subjected to a thermal treatment by means of which the oxidases are inactivated.

According to one production method, this inactivation is performed by subjecting the tea leaves to a flow of steam for 20 to 60 seconds, while according to another production method said inactivation is performed by placing the tea leaves in containers which are heated so as to provide a sort of partial steaming of the leaves.

The inactivation of the oxidases prevents or substantially hinders the oxidation of the catechins and accordingly maintains a green coloring for the tea and a taste which is closer to that of the freshly plucked leaf.

After this inactivation, a rolling step very similar to the rolling used to produce black tea is performed in the production of green tea as well.

The retention period provided in the production of black tea is replaced, in the production of green tea, with successive rollings and gradual partial dryings which alternate and gradually bring the product closer to its final form and degree of humidity. Once the green or black dry tea has been obtained, the different qualities are then selected and sorted; their most important distinctive element is the different percentage of younger leaves with respect to the older ones.

The gradual rise in the cost of labor has led to an increasing mechanization of tea production. First of all, an attempt has been made to mechanize the harvesting of tea leaves by organizing plantations in efficient layouts and by using machines to cut and harvest the first three leaves of tea. The organization of the cultivation of tea plants and the gradual improvements to these machines, however, have not yielded fully satisfactory results, since with mechanized harvesting the tea production process receives in input not only the first three leaves but also the fourth leaves and sometimes the fifth leaves and the stalks of the buds as well, which have a significantly lower content of noble substances than the leaves.

This of course entails, as a contrast to the reduction in labor costs, a decrease in the quality of the tea produced, since the tea still contains at the end of the process, in less than perfectly controlled doses, old and young leaves and stalks which in traditional manual production were better sorted and, respectively, rejected or more precisely included in controlled doses.

The rolling operation has also been mechanized by adopting machines which perform true roller crushing and machines which cut the tea leaves in order to equally rupture the walls of the cells in order to release the oxidases and thus start the oxidation processes.

The mechanization of this step, owing to the fact that it produces a fragmentation of the leaves, makes it practically impossible to distinguish the younger leaves, which are thinner, from the older leaves, which are thicker, and therefore inevitably increases the difficulty and reduces the effectiveness of the subsequent selection and sorting of the various qualities.

For many leaves, rolling performed mechanically is incomplete and accordingly needs to be repeated. For this reason, several rolling cycles are usually provided for, performing intermediate screenings in order to separate the leaves that have not been processed completely, and which must therefore be subjected to rolling again, both from the leaves that have been completely processed, which are instead sent to the subsequent treatment step, and from the stalks, which at this very stage of the process separate physically from the leaves.

The drying operation, known as firing, is performed in suitable ovens in which the temperatures and the humidity levels of the product being processed are controlled and regulated continuously according to diagrams designed specifically and adapted both to the characteristics of the incoming material and to the type of result to be obtained, in order to have, within the preset times, the correct and appropriate degree of evaporation.

In mechanized production cycles, the selection and sorting operation is performed by successive screenings by using a plurality of cascading vibrating screens, in which the dry crude product, entering from above, encounters a first vibrating screen with a wider mesh which retains and separates the coarser fragments, while the fragments that pass through it fall onto the subsequent screen which has a slightly smaller mesh and separates out a second fraction of the product which has smaller dimensions than the first one and so forth for 5-10-12 times until the finer particulates are separated. In mechanized cycles this screening operation, owing to the fact that mechanized rolling has produced a fragmentation of the leaves, is scarcely effective and can lead to different results in terms of quality of the selected products. In practice, although the screening operations undoubtedly allow to separate the various parts that compose the dry tea as a function of their various fragment sizes, they are unlikely to be capable of performing a perfect differentiation of the various parts of the bud in terms of quality.

Mechanization, by increasing the variety of the components of the bud introduced in the production cycle and by not allowing an accurate and precise discrimination of these components during production in order to allow their specific treatment, has significantly reduced the average quality of the product.

During the various steps of mechanized production, average treatment conditions are inevitably encountered which can be considered satisfactory or acceptable but which, if examined in terms of the individual components of the bud, are unsatisfactory or inadequate and negatively affect the qualitative result.

Thus, for example, during withering the smaller and thinner young leaves lose water much more rapidly than the older and thicker leaves and even more than the stalks, and accordingly they are excessively dehydrated when they reach the rolling step; in rolling, the younger leaves are much more sensitive to mechanical action than the old leaves and the stalks; the fermentation times adopted cannot be equally optimum for the various different leaves, since as mentioned the concentration of the substances involved in the fermentation varies according to the age of the leaf; moreover, drying as performed at present, i.e., in an undifferentiated manner on the entire mass of the product, leads to less than entirely satisfactory results, since in order to achieve an average humidity of approximately 4- 5% more humid stalks and old leaves are obtained, while the younger and therefore qualitatively more valuable leaves are often dried excessively if not indeed burnt.

In summary, while traditional manual production allowed good to excellent results, albeit with prohibitive costs, the onset of mechanization in production has significantly reduced production costs but the quality of the product has dropped distinctly.

Disclosure of the Invention

The aim of the present invention is to solve the above-cited problems by providing a method for the production of tea in particulate or leaf form which, although allowing considerable savings in terms of labor, achieves better qualitative results than the mechanized processes currently used. Within the scope of this aim, an object of the present invention is to provide a method which allows to reduce or eliminate the rolling operation, thus also reducing the overall costs of the apparatus required for tea production.

Another object of the present invention is to provide a method which can be adopted both for the production of black and oolong tea and for the production of green tea.

Another object of the present invention is to provide a method which allows a more effective selection and sorting of the parts that compose the bud of the tea subjected to the treatment.

This aim, these objects and others which will become apparent hereinafter are achieved by a method for the production of tea in particulate or leaf form, comprising a step of harvesting the parts of the tea plant to be treated, characterized in that it comprises a step of freezing said parts of the tea plant at a temperature which is substantially between - 0°C and -150°C to cause the rupture of their cell walls and of the sub-cell organelles due to the freezing of the protoplasm, and a thawing step of causing a mixing of the oxidases and substrates which escape from the sub-cell organelles which are ruptured by the freezing step; after said freezing step and before said thawing step said parts of the plant are subjected to a mechanical action to detach the leaves from the remaining parts of the plant that are subjected to treatment.

Further characteristics and advantages of the present invention will become apparent from the following detailed description of a preferred but not exclusive embodiment thereof, illustrated hereinafter only by way of non-limitative example.

The method according to the invention comprises a step for harvesting the parts of the tea plant to be subjected to treatment, which are constituted by the first leaves of the bud of the tea plant.

This harvesting can be performed easily by means of the machines currently used for this purpose, and the fourth and fifth leaves and the stalks that compose the bud can thus be included in the harvesting.

Then the parts of the plant thus plucked are subjected to a step for quick freezing to a temperature substantially between -40°C and -150°C, preferably between -70°C and -100°C, for a time which can vary between 5 and 20 seconds according to requirements.

This freezing operation can be performed by means of conventional freezing systems and in particular it can be performed by striking with a stream of liquid nitrogen the parts of the plant being treated. This freezing method has the advantage of requiring reduced plant costs and low costs for the purchase of liquid nitrogen.

This freezing step, followed by a thawing described in detail hereinafter, effectively replaces the rolling operation of conventional art. Owing to the fact that the plant cells are delimited by semipermeable walls which have a certain thickness and rigidity and that said walls enclose a substance which is very rich in water, known as protoplasm, and in which vital functions occur which are suitable for nutrition, reproduction and for specific functions depending on the tissues to which they belong, quick freezing initially stiffens the cell membrans, almost vitrifying them, and then freezes the water in the protoplasm, with a consequent increase in volume which necessarily leads to fragmentation of the cell walls and of the sub-cell organelles and to tissue necrosis.

In practice, the step allows a co-mixing of oxidases and substrates which leak from the sub-cell organelles which are ruptured by the freezing step and accordingly an effect is obtained which is comparable to the effect produced by "rolling" but is undoubtedly more uniform, controllable, manageable and repeatable.

If one wishes to produce black tea, the freezing operation can be preceded by a withering operation, reducing by 30-40% the humidity that is present in the parts of the plant that are subjected to the treatment, which is approximately 78-75% at harvesting time. This withering can still be performed even when it is not necessary, since it does not hinder the freezing operation, although it slows the subsequent oxidations. If one wishes to produce green tea, a step for inactivating the oxidases by heat is performed before the freezing operation. This oxidase inactivation step can be performed in a per se known manner, for example by striking the plucked plant parts with a flow of steam.

In black tea, oolong tea and in green tea, after the freezing step and before thawing, the parts of the tea plant that are subjected to treatment undergo a mechanical action to detach the leaves of the plant from the stem portions that support them.

This mechanical action can be performed by pressing the parts of the plant being treated, for example by roller crushing. In particular, in a preferred but not exclusive system, this mechanical action can be constituted by an extrusion of the parts of the plant that are subjected to treatment through a duct which tapers gradually.

This mechanical action, performed on the parts of the plant that are still frozen, in a condition of particel or total cristallization, and therefore highly brittle, causes the leaves to break at the petiole that provides connection to the stem and possibly in other more fragile parts of the leaves, thus possibly allowing to distinguish between the blade of the leaf and the larger nervures.

After this mechanical action, the parts of the plant that are subjected to treatment undergo separation into the various fractions that compose them. This separation is preferably performed by feeding the parts of the plant that are subjected to treatment, preferably still frozen, into an upper region of a treatment chamber and by striking said parts with an air stream which has a substantially horizontal orientation and a speed which decreases from the top downward. In this manner the leaves and the other parts fall, separated from each other, into collection hoppers which are arranged on the bottom of the chamber and are mutually spaced along the advancement direction of the air stream according to the different ratio between the mass and the air impact surface of the various parts of the mixture introduced in the treatment chamber. In this manner it is possible to obtain, inside the various hoppers, in the following order: stems, thicker and therefore older leaves, thinner and therefore younger leaves, and small fragments of leaves or particulates, all perfectly separated from each other.

This separation undoubtedly provides a qualitatively better sorting than conventional methods and allows to compensate for any errors in mechanized harvesting, since the older leaves, which accordingly have a higher ratio of mass to impact surface, and the stalks can be easily separated from the more valuable parts and can be then appropriately introduced in controlled doses in less valuable products or optionally eliminated. After this separation operation, the parts of the plant that are subjected to treatment, after thawing and after optionally eliminating the unusable parts, can be subjected to the treatments that are usually performed after rolling, i.e., oxidation or fermentation and drying. Oxidation or fermentation occurs as a consequence of the contact, inside the tissues, of the oxidases with the catechins released by the preceding freezing operation, as before explained.

It should be noted that these further treatments can be performed on the various parts of the product being processed while they are separated from each other, so as to be able to vary, according to the type of said parts, the timings, temperatures and the other parameters of the process. In this manner an optimum oxidation is obtained, according to the intended target values of the various sortings of separated products, as well as an optimized drying thereof, without, the danger of having excessively moist parts or excessively dried or even burnt parts, to the benefit of a better quality of the finished product. In practice it has been observed that the method according to the invention fully achieves the intended aim and objects, since by achieving a more complete and uniform rupture of the cell walls and by allowing a more selective and accurate subsequent separation of the various parts of the plant subjected to the treatment it allows to obtain a product which is qualitatively better with production costs which are comparable to, or even lower than, those required by known mechanized processes.

The method thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; all the details may also be replaced with other technically equivalent elements. The disclosures in Italian Patent Application No. MI98A001729 from which this application claims priority are incorporated herein by reference.

Claims

1. A method for the production of tea in particulate or leaf form, comprising a step of harvesting the parts of the tea plant to be treated, characterized in that it comprises a step of freezing said parts of the tea plant at a temperature which is substantially between -40┬░C and -150┬░C to cause the rupture of their cell walls and of the sub-cell organelles due to the freezing of the protoplasm, and a thawing step of causing a mixing of the oxidases and substrates which escape from the sub-cell organelles which are ruptured by the freezing step; after said freezing step and before said thawing step said parts of the plant are subjected to a mechanical action to detach the leaves from the remaining parts of the plant that are subjected to treatment.

2. The method according to claim 1, characterized in that said freezing is performed by bringing the parts of the plant to a temperature which is substantially between -70┬░C and -100┬░C.

3. The method according to one or more of the preceding claims, characterized in that said freezing is performed for substantially between 5 and 20 seconds.

4. The method according to one or more of the preceding claims, characterized in that said mechanical action comprises a step of pressing the parts of the plant that are subjected to treatment.

5. The method according to one or more of the preceding claims, characterized in that said mechanical action comprises a step of roller crushing the parts of the plant that are subjected to treatment.

6. The method according to one or more of the preceding claims, characterized in that said mechanical action comprises the extrusion of the parts of the plant that are subjected to treatment through a duct which gradually tapers.

7. The method according to one or more of the preceding claims, characterized in that after said mechanical action for detaching the leaves from the remaining parts of the plant, said parts of the plant are subjected to separation into the various elements that compose them.

8. The method according to one or more of the preceding claims, characterized in that said separation is performed as a function of the ratio of mass to air impact surface of the various elements that compose the parts of the plant that are subjected to treatment.

9. The method according to one or more of the preceding claims, characterized in that said separation is performed by feeding the parts of the plant subjected to treatment into an upper region of a chamber and by striking said parts of the plant with an air stream which flows in a substantially horizontal direction and with a speed which decreases from the top downward in order to make the leaves and the other parts of the plant fall so that they are mutually separate into collection hoppers which are mutually spaced along the advancement direction of said air stream, according to the different ratio of mass to air impact surface of the elements that compose said parts of the plant.

10. The method according to one or more of preceding claims, characterized in that said separation is performed while the parts of the plant are still frozen.

11. The method according to one or more of the preceding claims, characterized in that after said thawing step the parts of the plant that are subjected to treatment are left to ferment (oxidize).

12. The method according to one or more of the preceding claims, characterized in that before said freezing step said parts of the plant are subjected to a step for inactivating the oxidases by heat.

13. The method according to one or more of the preceding claims, characterized in that said step for inactivating the oxidases is performed by striking with a flow of steam the parts of the plant that are subjected to treatment.

14. The method according to one or more of the preceding claims, characterized in that after said fermentation step the parts of the plant subjected to treatment are dried.