GB2214786A

GB2214786A - Processing vegetable material

Info

Publication number: GB2214786A
Application number: GB8802630A
Authority: GB
Inventors: Bruin Hoogstad; Roula Abdel Salam Rafi Kamhawi
Original assignee: Unilever PLC
Current assignee: Unilever PLC
Priority date: 1988-02-05
Filing date: 1988-02-05
Publication date: 1989-09-13
Also published as: GB8802630D0

Abstract

Method for processing vegetable material comprising the steps of (a) mixing the vegetable material with a liquid (b) feeding the mixture to a liquid permeable moving belt, whereabove one or more pressing elements are arranged (c) moving the belt such that the mix is subjected to an increasing pressure (d) collecting the liquid and/or the residue. Preferably the method is used for extracting tea leaves with water in a period from 2-8 minutes. <IMAGE>

Description

Method for processing vegetable material The present invention relates to a method for processing of vegetable material, more specific to a method for separating extracted tea leaves from water on a large scale in a short time.

Separation of vegetable material from a liquid is for instance done at the end of a period of extraction.

Extraction of vegetable materials is a well-known process in the food industry, materials suitable for extraction are for instance leaf materials such as tea, herbs or peppermint or ground bean materials such as coffee, chicory or soy. Water or aqueous solutions have proved to be preferred solvents.

Ideally vegetable material should only be extracted for a period of less than 10 minutes, preferably 2-7 minutes, starting with boiling water. If tea leaves are extracted ideal extraction times are 5-6 minutes, a longer extraction period dissolves an excess of tannins and other vegetable extracts. After the extraction period tea leaves are to be separated from the brewing liquid.

In domestic tea brewing ideal separation conditions are reached by quickly removing the tea-bag from the teapot after a few minutes of brewing. On industrial scale it was until now mechanically impossible to contact the tea leaves with water and separate the extract within this short period.

Alternative processes for extracting tea on industrial scale have been proposed for instance in US patent 3,065,077 (A.R. Mishkin). These processes require however long extraction periods and often give extracts which are less in quality than fresh home-brewed tea.

It is an object of the invention to provide a method for processing vegetable material wherein the material is separated from the liquid, which method can be used on a large scale and which only requires a short time without negative effects on the quality of the product. It has been found that this is possible by using a so-called pressure belt device or similar equipment for vegetable material/liquid separation.

Pressure belt devices have been known in itself since a long time. Up till now they were mainly used in wastewater cleaning operations, paper industry or for squeezing fruit. Standard pressure belt devices contain a transport band for supporting the processed material and one or more pressing elements for subjecting an increasing pressure to the material during movement of the belt.

The invention therefore relates to a method for processing vegetable material comprising the steps of (a) mixing the vegetable material with a liquid solvent (b) feeding the mixture to a liquid permeable moving belt, whereabove one or more pressing elements are located (c) moving the belt such that the mix is subjected to an increasing pressure (d) collecting the liquid and/or the residue.

The vegetable material can be any vegetable material commonly used in food applications. Preferred vegetable materials are alkaloid containing materials e.g. ground coffee or tea. Best results were obtained in extracting and thereafter separating tea leaves from water.

The vegetable material can be mixed with liquid solvent e.g. water in any ratio suitable for the purpose as desired. In extracting the weight ratio liquid: vegetable material will normally be more than 1, preferably more than 5, most preferred between 5 and 500. Any other food grade solvent can be used.

The liquid can have any temperntlXre as long as adequate interaction between vegetable material and the liquid is effected. For low temperature extracts the liquid will generally be at ambient temperature, for high temperature extracts temperatures above 70"C, preferably between 85-105"C are used. If desired the vegetable material can be subjected- to a two stage extraction e.g.

by first extracting with cold and subsequently with hot liquid.

After mixing and optional resting the mixture is fed to the conveyor belt which should be permeable to liquid and which is moveable. Above the belt are pressing elements arranged, these can be constructed from any mechanical means suitable for applying pressure.

Preferred is the use of a second top belt supported by pressure rollers to effect a progressive increase in pressure during transport of the mix on the belt.

Most preferred is the transporting of the mixture through three zones, a free run zone, a wedge zone and a surface pressing zone. In the free run zone the mixture of liquid and vegetable material is put onto the moving water permeable belt without the exertion of mechanical pressure onto the mix. In this zone the liquid will be separated from the vegetable material by gravity forces.

In the wedge zone the mix is slightly compacted e.g. by a top belt which gradually approaches the bottom belt, in this zone free liquid which is situated between the vegetable pieces is substantially released. In the surface pressing zone the pressure onto the mix is increased for instance by feeding the top and bottom belts through a set of rollers. In this stage mainly liquid which was absorbed by the vegetable materials is squeezed out thus giving a low moisture vegetable residue.

This low moisture vegetable residue is very dry compared to vegetable materials rfcF .yp eeparored from a 1iqiid by other methods. This renders the residue extremely easy to handle.

A preferred method according to the invention involves the extraction of vegetable material with water. Most preferred is the extraction of tea leaves. In doing this, the extract is collected for instance in a container which is situated below the water permeable conveyor belt.

It is believed that the excellent quality of the extract obtained with this method is due to the short time required for carrying out the process. Preferably the extraction will be carried out in a time period of 2-8 minutes, most preèrred 5-4 minutes, which is comparable to the domestic brewing period.

Although not fully understood another possible explanation for the high quality of the final extract could be that the final extract is in fact a mixture of extract fractions obtained by increasing the pressure on the mixture. Although not fully understood it is believed that the extract fractions which merely drip through the belt by gravity will have a different composition from the extract fraction obtained by severely pressing the mixture. The final extract will be a mixture of different extract fractions, surprisingly this balanced mixture provides an excellent taste.

The obtained extract can be further processed according to well-known methods like drying, concentrating, freeze-drying etc In other embodiments of the invention it is the aim to collect the vegetable residue. During decaffeination of tea or coffee the method according to the invention can for instance be used to effect a quick separation between the vegetable material and the caffeine solvent.

As stated before the residue is generally very dry which allows easy handling. Furthermore it has been found that the possible short contact time between solvent and vegetable material results in good quality products.

The invention will be further illustrated by means of the following figures and examples: Figure 1 shows a pressure belt device preferably used for carrying out the method according to the invention comprising a feeding pipe 1 for feeding a mixture of liquid and vegetable material 2 to a first bottom conveyor belt 3 which is perforated and thus liquid permeable. Initially the mixture passes through the free-run zone wherein liquid is separated from vegetable material by gravity and collected in container 4. Above the bottom belt a top conveyor 5 is arranged which gradually approaches the bottom belt in de wedging zone.

The liquid obtained in this zone is also collected in container 4. In the surface pressing zone the two conveyor belts pass through a set of rollers 6 which effect the final separation of the vegetable material.

The vegetable residue 7 is discarded or further processed.

Figure 2 shows in more detail the free-run zone showing the permeable bottom belt 3 and the mixture of vegetable material and liquid 2.

Figure 3 shows in more detail the wedge zone wherein the top belt 5 approaches bottom belt 3 thus compacting the mixture of vegetable material and liquid.

Figure 4 shows the surface pressing zone in which roller 6 effects a further compaction of the mixture of vegetable material and liquid.

Fxam le 20 Kg of standard black tea leaf was mixed with 200 litre water having a temperature of 97"C. The mixture was stirred for 2 minutes and fed to a water permeable moving belt. A first fraction of the extract dripped through the belt by gravity, a second fraction of the extract was obtained by compacting the mixture in the wedging zone, a third fraction was obtained in the surface pressing zone. The three fractions were collected in one container and further processed.

The total process was carried out in about 4 minutes.

The final extract had a solids content of 3,5%. The quality of the obtained extract was judged to be excellent and comparable to the standard home brewed tea.

Claims

1. Method for processing vegetable material comprising the steps of (a) mixing the vegetable material witb a 1 uid (b) feeding the mixture to a liquid permeable moving belt, whereabove one or more pressing elements are arranged (c) moving the belt such that the mix is subjected to an increasing pressure (d) collecting the liquid and/or the residue.

2. Method according to claim 1, characterised in that the liquid is water which is collected as extract.

3. Method according to claim 1 or 2, characterised in that the vegetable material is tea.

4. Method according to claim 1, 2 or 3, characterised in that the steps a-d are carried out in a time period from 2-8 minutes.

5. Method according to claims 1-4, characterised in that the vegetable material is contacted with water having a temperature of 85-105"C.

6. Method according to claims 1-5, characterised in that the mix is subjected to an increasing pressure in three zones, a free run zone, a wedge zone and a surface pressing zone.