NZ505790A - Method for manufacturing sterilized corks involving microwave irradiation - Google Patents

Abstract

The bulk cork is, or corks are, subjected to microwave radiation of 2-1000 watts per kg over an interval of 2.5-30 min. The preferred power is 50-200 watts per kg, in a conveyor oven operating continuously. Water content is reduced from 12-15 wt% to 6-10 wt%. Composite cork in manufacture is submitted to the microwave radiation for more rapid binder polymerization and setting. In addition, stabilization of adhesive between natural cork sections is accelerated.

Description

New Zealand Paient Spedficaiion for Paient Number 505790 17482 .3 PCT/EP99/00174 filed January 14, 1999. Translation of application as filed.

Treatment Method for Cork Material and Corks The present invention concerns a treatment method, in particular, for the sterilization and for the reduction of chemical contamination in cork material and corks.

Natural cork from the bark of the cork tree (Quercus suber) has been utilized since antiquity in large quantities for the sealing of bottles, tubes and the like. Bottle corks for high quality products, e.g. wine and sparkling wine, can be produced in differing manners and have different compositions. One can stamp the corks out of the cork bark of the cork oak to obtain a single piece of cork (natural cork). Alternatively, conventional agglomerate corks can be made from ground cork material with the addition of a binding agent either as individual or extruded products. Natural cork sheets and agglomerate bodies can also be combined into corks.

The harvested and stored plates of cork bark (cork wood) are prepared for further processing via a boiling process during which a change in the cell structure effects the high elasticity of the cork. Contaminants can thereby gain access into the cork material due to impurities in the water. Air 2 drying is normally used to adjust the water content of the cork plates to the desired value throughout the subsequent storage period (stabilization) of normally up to 21 days. During this period, bacteria or mold can develop in and on the cork material.

The natural cork is subsequently stamped out of the cork bark using a suitable device and subjected to a chemical bleaching process preferentially based on peroxide or on chlorine bleach. Further processing then follows using differing external processing agents. Natural cork sheets for sparkling wine corks or composite wine corks made from a combination of natural cork sheet and agglomerate bodies are stamped out of thin layers of natural cork, the outer layers of which are previously removed.

Agglomerate corks are produced from ground unused residue in natural cork production (ca. 60% of a cork plate). The granulated material is, in dependence on the quality of the agglomerate cork material to be produced, cleaned to a greater or lesser degree, mixed with bonding agents (e.g. polyurethane glue) and shaped in an extrusion procedure or in a single piece processing procedure. For the case of combined corks, agglomerate bodies and natural cork sheets are joined using various glues.

During the course of these differing production processes, a strong increase in the microorganism content on or in the 3 cork or corks can occur for various reasons, either due to new external contamination or due to an improvement m environmental conditions associated with the increase in internal temperature and moisture. Modern gluing techniques require long stabilizing periods during the course of which a large increase in the number of microorganisms can occur.

In addition, a degree of chemical contamination can also occur in the cork material for differing reasons. Cooperation between microbiological metabolism selectivity in the presence of chemical contaminants can lead to a strong enrichment in metabolism products, such as the conventional 2,4,6-trichloroanisol causing the characteristic cork flavor. The production of this latter material, according to the current state of knowledge, is only due to microbiological metabolization of chemical precursors. Two other metabolizing products are l-octen-3-ol, causing the strong wild mushroom aroma and guaiacol, causing a medical/or burnt taste discoloration. In addition, a plurality of chemical contaminants can lead directly, i.e. without intermediate metabolization, to tainting accents.

To solve or to reduce the above mentioned problems in conventional industrial cork production, the cork material or the corks are treated with peroxides. However, this does not lead to deep-acting sterilization, since the solutions do not penetrate into the cork or only to a very insignificant amount due to the poor permeability of cork with regard to 4 liquids. In addition, a reduction in chemical contaminants is not thereby achieved. Adjustment of the water content using the currently applied hot air treatment is associated with wide fluctuations, since cork is an extraordinarily good heat insulator.

It is thereby the underlying purpose of the present invention to create a treatment method for cork materials and cork by means of which not only the surface but also the inner portions of the respective cork are reached with the desired sterilization without damaging the cork material itself and which can be carried out under economical conditions, wherein contamination of the cork is also reduced. In addition, agglomerate corks and combined corks should be improved with regard to the curing of the glue.

This purpose is achieved through the treatment method articulated by the features in the main claim and enhanced by the features of the dependent claims.

In order to guarantee an event treatment, in dependence on the manufacturing phase in which microwaves are applied, cork wood plates (e.g. following the cooking procedure) or previously stamped-out cork, cork sheets, cork granulated material, freshly glued cork or other intermediate and end products are appropriately dispensed onto a conveyor belt and transported though a microwave installation to be irradiated with microwaves.

Since the materials being treated have differing compositions, quality and water content, the energy used as well as the irradiation time for the microwaves has to be adjusted to the respective initial conditions (cork type or types, cork quality and water content) and to the desired result.

The energy and the processing time are thereby determined in dependence on need and checked by suitable analytic methods. These quantities depend on additional boundary conditions such as the moisture and the temperature of the ambient air as well as on the size and configuration of the microwave installation used.

In order to guarantee a homogeneous irradiation of the cork being processed, the corks are either irradiated in a closed microwave oven or preferentially in a continuous conveyor belt microwave oven. An irradiation dose of 15 to 1000 W per kg of cork during an irradiation time of 2.5 to 30 minutes has turned out to be particularly appropriate. A microwave oven power of 0.1 to 4 kW/h per kg of cork, preferentially approximately 0.5 kW/h per kg, normally leads to very good sterility for the cork material. Lower power levels only lead to a partial drying of the cork but not to sterilization. In fact, lower irradiation doses have led to increased contamination compared to cork which has not been treated with microwaves. This is due to the production of 6 temperatures within the cork of 30 to 40°C which are advantageous for an amplified replication of microorganisms. Irradiation exceeding the power levels indicated above leads to an overheating of the cork material and thereby to excessive drying out and decomposition so that such treatment should be avoided. Complete sterilization is normally achieved. The risk of microbiological production of chemical compounds in cork which can be sensed and which are the primary causes of subsequent negative aromatic and taste changes in wine, sparkling wine and other beverages sealed with corks, is thereby substantially reduced.

As a positive side effect of the sterilization, corks having relatively strong initial moisturization with water contents of approximately 6 to 20%, as are obtained following bleaching and subsequent washing processes, are homogeneously dried to an even moisture of approximately 4 to 10%, which is optimal for processing.

A reduction in chemical contamination is also effected under these conditions. The risk of direct taste discoloration due to the migration of contaminants, which can lead to aromatic or taste changes without an intermediate microbiological metabolization, are significantly reduced by the processing as is the risk of taste discoloration due to the migration of contaminants which are first transformed into compounds which can be sensed after microbiological metabolization. 7 With regard to the production of agglomerate corks or of combined corks comprising agglomerate corks and natural cork sheets (e.g. sparkling wine corks, so-called 1+1 corks), the method leads to a more rapid polymerization and curing of the polyurethane binding agent currently used. A particular improvement is achieved in the presently used "sheet glue" (binding the agglomerate blank of the sparkling wine cork or of the 1+1 cork to the natural cork sheet) with which the so-called "stabilization phase" subsequent to gluing and prior to further processing can be substantially reduced.

By means of the thoroughly precise adjustment of the water content of the cork and of the intermediate cork product with the assistance of the new method, a significantly higher quality is achieved with regard to the application and binding of external processing agents which determine the sealing behavior of the cork and, moreover, guarantee a proper closing and opening of the bottles.

The substantial advantage of the microwave treatment compared to the thermal method is due to a fundamental shortcoming common to all types of thermal cork treatment: its substantially low heat conductivity. Using a thermal treatment applied externally, the required temperature increase is limited to the outer region of the cork or corks and decreases continuously towards the inner portion of the cork. 8 In contrast thereto, the microwaves excite, with the speed of light and with associated very high penetration depths, water and other molecules which can be excited by microwaves and which are located in the material being processed to thereby lead to a very rapid and homogeneous warming-up or heating of the material being processed without formation of temperature gradients. The higher the water content of the material being treated, the more effective the transformation of the microwaves into heat. This explains the bacterial reduction and sterilizing effect of the microwaves, which is due to a very effective transformation of the microwaves into heat in the cell water of the microorganisms to kill-off same.

The water content of the microwave-treated material can be continuously monitored under production conditions using appropriate sensor technology (contactless IR-measurement techniques, pyrometers, etc.), since the reduction in water content is associated with a reduced transformation of microwave energy into heat permitting a precisely calculable and predictable temperature dependence in the material being processed.

The reduction in chemical contamination is due: - to direct excitation of the compounds to be removed and thereby to a heating up and increased vapor pressure of the corresponding components, leading to a rapid out-gassing of the cork material, 9 and/or - to a co-distillation effect occurring during evaporation of water out of the cork material being processed and/or - to an increased out-gassing due to the increased temperature in the cork materials associated with the excitation of the water.

In a preferred embodiment, the cork material is continuously transported through a continuous conveyor belt microwave installation to achieve the purposes delineated above. Clearly, it is also possible to use other conventional types of microwave continuous flow ovens or dryers which have been commercially available for several years.

The experimentally utilized microwave continuous flow oven permitted adjustments of the microwave power in a heating zone of approximately 2000 mm up to 4.0 kW, wherein the product to be irradiated could be transported on a conveyor belt having a belt speed between 0 and 2 m/min with a conveyor belt width of 290 mm. In order to investigate sterilization, the cork was placed together on the conveyor belt and transported through the oven with a throughput velocity between 2 to 10 minutes. The microwave power was between 500 and 4000 Watt. As can be seen in table 1, the microbiological activity of non-treated cork is increased by weak microwave irradiation, wherein up to a doubling of the activity can occur which, with the subsequent higher irradiation density used in accordance with the invention, rapidly sinks to approximately zero.

Table 1: The Microwave Treatment of Cork for Purposes of Sterilization: Energy acceptance per kg Cork in Watts non-treated 1.5 100 microbiological Activity (CORA Factor) 1.075 1.055 1.260 2 .020 0 . 019 Table 2 shows the reduction of three exemplary chemical contaminants (trichloromethane, dichlorobenzole and 2,4,6-trichloroanisol). The microwave treatment was thereby carried out at an irradiation of 4 kW with an oven flow through time of 10 minutes with a charge of 1 kg of cork, a reasonable irradiation for successful sterilization. It has turned out that approximately 90% of both products are driven off. The out-gassing is thereby probably due both to an increase in the vapor pressure of the respective component through heating of the cork material as well as to a co-distillation evaporation together with the expelled water. 11 Table 2: The Microwave Treatment of Cork for Purposes of Chemical Decontamination: a) Energy acceptance Trichloromethane per kg cork in Watt Hg/g cork untreated 125 100 12 .5 b) Energy acceptance Dichlorobenzole per kg cork in Watt fig/g cork non-treated 8.9 100 O 00 c) Energy acceptance 2,4,6-trichloroanisol per kg of cork in Watt ng/g cork untreated 100 2.5 The manufacturing and treatment method is described more closely below for differing types of cork: In all cases, the bark of the cork oak is initially harvested, subsequently subjected to a curing process, and boiled. For purposes of sterilization and pre-sterilization or decontamination, the cork bark pieces are then subjected 12 to a microwave energy of 15 to 250 W/(kg cork), wherein the energy applied depends on the moisture of the cork bark pieces.

For production of single piece natural corks, same are subsequently punched out of the cork bark pieces and are then subjected to renewed irradiation with microwaves at a power of 50 to 200 W/(kg cork) to achieve substantial sterilization and decontamination. Natural cork sheets used for sparkling wine and champagne corks are produced and processed in a similar manner.

After scraping-off the natural corks, same are bleached with H202 (peroxide) and subsequently dried to a desired moisture content through renewed irradiation of microwave energy of 15 to 150 W/(kg cork).

For the production of agglomerate corks or combined corks, a granulated material is produced from material residues occurring during the punching-out of the natural cork, the moisture of which is adjusted to a desired value through irradiation of microwave energies from 50 to 200 W/(kg cork) and thereby simultaneously sterilized and decontaminated. A cork blank is then produced from the granulated material with the addition of glue in a single piece production method or in extrusion process, which is glued to the previously produced natural cork sheet. The corks produced in this manner are subjected to irradiation with microwave energy of

Claims (1)

13 20 to 150 W/(kg cork) for stabilization of the glue, wherein an approximately complete sterilization and decontamination are thereby simultaneously achieved. 4 to 6 weeks of time can sometimes pass between production of the corks and delivery to customers, so that the cork may have an insufficient amount of moisture (less than 4%) in certain isolated cases. In this event, the corks are moistened by spraying on water and the moisture content is subsequently adjusted to the desired level using the microwave energy, wherein renewed sterilization and decontamination are effected. 14 50 o 7 Claims 5 10 2 . 15 3 . 20 4 . 25 5 . Method for manufacturing single pieces of decontaminated and sterilized corks from cork material, wherein the corks are stamped out of pieces of cork bark and subsequently subjected to irradiation with microwaves with a power of 50 to 200 w per kg of cork for a duration of 2.5 to 30 minutes to decontaminate and sterilize, the cork subsequently being ground and bleached and/or washed and then subjected to renewed irradiation with microwaves with a power between 15 to 150 W per kg of cork. The method of claim 1, wherein the corks are disposed next to one another on a conveyor belt and transported therewith through a continuous flow-through microwave oven. The method of claim 1 or 2, wherein the corks are moistened 4 to 6 weeks after manufacture by spraying water, wherein the moisture content is adjusted to a desired level through the influence of microwave energy. The method of claim 3, wherein the moisture content is adjusted to 4 to 10 % by weight. Method for manufacturing decontaminated and sterilized cork from a combination of agglomerate and cork sheets, wherein the cork sheets are stamped out of pieces of cork INTELLECTUAL PROPERTY OFFICE OF N.Z. 1 <>' JAN 2002 RECEIVED 15 bark and subsequently subjected to an irradiation with microwaves with a power of 250 W per kg of cork for a duration of 2.5 to 30 minutes for decontamination and sterilization, wherein a cork granulate is produced from residual cork and, for sterilization and decontamination, is subjected to irradiation with microwaves with a power of 50 to 200 W per kg of cork for a duration of 2.5 to 30 minutes, wherein a cork blank is subsequently produced from the cork granulate by the addition of a glue, the cork blank then being joined with and glued to the independently produced cork sheets. The method of claim 5, wherein the cork granulate and/or cork sheets are disposed next to one another on a conveyor belt and transported therewith through a continuous flow-through microwave oven. The method of claim 5 or 6, wherein the moisture content of the cork granulate and/or cork sheets is adjusted to 4 to 10 % by weight through irradiation of microwave energy. The method of any one of the claims 5 through 7, wherein the glued cork is subjected to renewed irradiation with microwaves of power between 20 to 150 W per kg of cork to stabilize the glue. 16 i - _ ' ■' . . j ■ / ]' > » 9. A single piece of decontaminated and sterilized cork manufactured by the method of claim 1. 10. A decontaminated and sterilized cork manufactured from a 5 combination of agglomerate and cork sheets by the method of claim 5. 11. A method as claimed in claim 1 substantially as herein described with reference to any example thereof. 10 12. A method as claimed in claim 5 substantially as herein described with reference to any example thereof. END OF CLAIMS