AU8085298A - Method and apparatus for applying volatile substances to materials - Google Patents

Description

I--i

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventors: Address of Service: DAVID JAMES LARK and ANDREW STIRLING INGLIS David James LARK and Andrew Stirling INGLIS BALDWIN SHELSTON WATERS MARGARET STREET SYDNEY NSW 2000 Invention Title: "METHOD AND APPARATUS FOR APPLYING VOLATILE SUBSTANCES TO MATERIALS" Details of Associated Provisional Application No. PO 8738 dated 22nd August, 1997 The following statement is a full description of this invention, including the best method of performing it known to us:- -v -2- METHOD AND APPARATUS FOR APPLYING VOLATILE SUBSTANCES

TO

i MATERIALS FIELD OF THE INVENTION This invention relates to a method and apparatus for the treatment of a material with a volatile substance entrained in a carrier gas. In a particular application of the invention, the method and apparatus is used to treat a food or pharmaceutical product or ingredient with a natural food acid such as carbonic acid for the purpose of achieving at least partial microbial decontamination and/or shelf-life extension.

0 BACKGROUND OF THE INVENTION: 10 Hitherto, conventional gaseous processes aimed at extending the shelf-life of materials prone to microbial spoilage have relied on modified atmosphere

(MAP)

procedures. In such procedures, the oxygen gas atmosphere surrounding the material is replaced with a food grade carbon dioxide and/or nitrogen atmosphere, and high barrier colaminate packaging is used to maintain the exclusion of oxygen from the package.

15 The slight acidity produced by the carbonic acid which results from the exposure of the material to carbon dioxide produces a fungicidal effect. However, MAP processes have disadvantages. That is, whilst it has been found that an extension of the shelf-life is achieved in respect of materials treated by the procedures, this extension is limited and considerable costs are involved including the cost associated with the specialised 20 colaminate film packaging used.

In copending Australian patent application No. 75449/96 (the entire disclosure of which is to be regarded as incorporated herein by reference), a method and apparatus is described for extending the shelf-life of materials prone to microbial spoilage by treating the materials with a volatile substance such as a natural food acid. The method described in this copending application involves prior evacuation of the vessel containing the material to be treated and, while this may lead to the more effective treatment of some materials, the inventors have now found that prior evacuation of the vessel containing the material is not necessi ry for the satisfactory extension of shelflife.

-;~;d;fYLY;lg~O ~rrrranrc~-- SUMMARY OF THE INVENTION: Thus, in a first aspect, the present invention provides a method of treating a material, comprising the step of contacting the material with a volatile substance entrained in a carrier gas.

Preferably, the material is a food or pharmaceutical product or ingredient and the method achieves at least partial microbial decontamination and/or shelf-life extension of the food or pharmaceutical product or ingredient.

The volatile substance is preferably microbicidal (eg. a natural food acid), and is preferably entrained in the carrier gas in saturating amounts. The material may be 10 contacted with the volatile substance/carrier gas mixture provided at pressures greater than ambient.

The method may be performed using a suitable vessel to contain the material during contact with the volatile substance/carrier gas mixture. The method may or may not involve evacuation of the vessel containing the material prior to contacting the 15 material with the volatile substance/carrier gas mixture.

In a second aspect, the present invention provides an apparatus for treating a material comprising: a vessel for containing the material; means for entraining a volatile substance in a carrier gas; and means for contacting the material contained within the vessel with the volatile substance entrained in the carrier gas.

Preferably, the vessel is adapted to allow the volatile substance/carrier gas mixture to be present at pressures greater than ambient. Open vessels may, however, also be used.

Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

1 -4- DETAILED DISCLOSURE OF THE INVENTION: Materials that can be treated by the method of the invention include any substance for which it is desired to have its chemical and/or physical characteristics altered by means of volatile substances. The method of the invention is suitable for microbial decontamination and/or control of a wide range of food products and ingredients including, but not limited to, baked goods such as bread, whole grain cereals, whole or diced berries. fruits or vegetables, prepared salads, nuts in their shell, nut meats in storage awaiting drying or while undergoing further processing, cheese, smallgoods, cured meats, chicken flesh, carcass on abattoir chains, sea and fresh water foodstuffs, and herbs and spices. The method of the invention is also suitable for microbial decontamination and/or control of pharmaceutical compositions and individual pharmaceutical ingredients, for head space sanitation and control of processing plant equipment. Still further, while the method of the invention may be used in isolation, it is also suitable for use with other treatment processes including for optimising dosing with anti-oxidants where high surface concentrations are desired, for the delivery of soluble food grade or other preservatives, for the depositing of substances onto surfaces with the possible assistance of electrostatic charges or in conjunction with MAP to increase the shelf-life of certain products.

The method of the present invention may be performed batch-wise or 20 continuously in a suitable vessel. Preferably, the vessel is adapted to allow the volatile g substance/carrier gas mixture to be present at pressures greater than ambient. For batch treatments, the material may be placed in the vessel using an infeed hopper attached to the vessel through, for example, a suitable valve. Alternatively, wrapped unsealed material may be placed in the vessel manually. For continuous treatments, the material may be placed in and out of the vessel by placing the material on a conveyor and passing the conveyor through the vessel and/or via rotary locks or other similar devices.

The duration of contact between the material and the volatile substance/carrier gas mixture may vary, as necessary, to achieve the desired aim. For example, for microbial decontamination of a material, the duration of exposure is that required to sufficiently reduce the total viable microbial content to a desired value and is dependant i* r~ on a number of variables including surface area of the material to be treated; flow rates of the carrier gas; surface water activity type and concentration of volatile substance and the bacterial and fungal bioburden of the material. The efficiency of the treatment method is also dependant on the interaction between the matrix geography and/or chemistry and the added volatile substance.

Typically, the duration of the contact between the material and the volatile substance/carrier gas mixture will be in the order of 0.05 to 2 mins, more preferably, 0.15 to 0.5 mins. However, in some applications of the invention, the duration of the S. contact between the material and the volatile substance/carrier gas mixture will be up to about 2 hours or more.

Contact between the material and volatile substance/carrier gas mixture may be achieved by means of one or more spargers. To assist contact between the material and volatile substance/carrier gas mixture, the vessel may be provided with means for tumbling andlor passing the material (eg. through falling under gravity) through the 15 volatile substance/carrier gas mixture.

The method of the present invention may comprise multiple (eg. up to 3 times) exposure (ie. contacting) of the material to a volatile substance/carrier gas mixture. The volatile substance(s) used in each exposure may be the same or different. Where multiple exposures are performed using a single vessel, the vessel may be evacuated between exposures and/or flushed with a suitable gas (eg. the carrier gas).

The volatile substance can be any substance which may be entrained in an inorganic or organic gas and which chemically and/or physically alter the treated material. For example, for microbial decontamination and/or extending the shelf-life of food and pharmaceutical products and ingredients, the volatile substance is preferably a natural food acid, more preferably carbonic acid and/or acetic acid, although any other natural food acid having microbicidal or preserving qualities can be used or other volatile preservative substances. Alternatively, a potentially residue-free chemical biocide such as hydrogen peroxide can be used. Mixtures of such volatile substances may also be used. The ratios of the component volatile substances in such mixtures will typically vary depending on the physical and chemical nature of the material being -6treated. However, for mixtures such as carbonic acid/acetic acid, carbonic acid/hydrogen peroxide and acetic acid/hydrogen peroxide, the ratio of the component volatile substances may be within the range of 1:10 to 10:1. Moreover, for the mixtures carbonic acid/hydrogen peroxide and acetic acid/hydrogen peroxide, the ratio of the component volatile substances is preferably within the range 1:5 to 5:1, more preferably, about 1:3.

The volatile substance is preferably entrained in the carrier gas by passing the carrier gas through a vessel or vessels containing the volatile substance or by other means by which a sufficient concentration of the volatile substance can be entrained in 10 the carrier gas without the formation of an aerosol. A multiple volatile substance/carrier gas mixture may be provided by mixing a group of parallel preferred volatile substance/carrier gas mixture streams after passing through their respective volatile substance sources or, alternatively, a single carrier gas stream may be passed through a series of volatile substance sources.

15 Alternatively, the volatile substance can be prepackaged with the carrier gas. The volatile substance is preferably entrained in the carrier gas in saturating amounts.

The carrier gas is preferably carbon dioxide and/or nitrogen gas which can be sourced from a cylinder containing the relevant compressed gas(es). The carrier gas, which is fully or partly stripped of the volatile substance after contact with the material 20 to be treated, may be recycled.

The volatile substance and/or carrier gas may be heated to increase volatility and hence concentration of the volatile substance in the carrier gas. Reduction in carrier gas usage and other efficiencies may result In the case of food products and ingredients, the limit to which the material to be treated can be contacted with the volatile substance/carrier gas mixture is generally determined by the flavour resultant from the acidulation of the product. That is, certain volatile substances (eg. acetic acid), have an unfavourable effect on flavour due to acidulation. However, other volatile substances (eg. carbonic acid). have been found to cause relatively little organoleptically detectable acidulation and can in some cases actually impart an appealing smoked flavour and/or aroma. In any case, the inventors -7have noted that the acidic flavour effects resulting from the method of the invention may recede during storage. Further, some materials end use involves heating or cooking (eg. crumpets), which will also decrease any lingering acidic flavour effects of the method. Mild surface drying to promote volatilisation of surface acids and posttreatment surface addition of alkalis such as approximately 0.2% w/w of sodium bicarbonate may also be used to reduce or avoid acidic flavour effects. It is also preferred that when the material to be treated has critical flavour specifications, the concentration of the volatile substance in the carrier gas be closely monitored and controlled.

S. I 10 Subsequent packing in packaging materials with poor gas barrier properties or small perforations may also assist in the diffusion of volatile substances from the surface of the material(s) treated by the method of the invention thus reducing any acidic flavour effects. Conversely, packaging with excellent gas barrier properties will aid to maintain an atmosphere of volatile substances thus enhancing the preservative 15 effect of the method. Accordingly, the barrier properties of the packaging may be chosen to suit the treated material.

The material to be treated should ideally have a minimum surface water activity of approximately 0.85 to allow the volatile substance to quickly transfer across from the carrier gas. An A, of approximately 0.95 will allow near optimum 20 transference rates and therefore minimum exposure times. To optimise transfer rates it may be appropriate to dose all the gaseous mixture required to an over-pressure of 0.01- 0.25 bar (7.5-190mm Hg) and up to 3 bar (2250mm Hg) above atmospheric pressure and allow the appropriate contact time. Lower A, foodstuffs without the addition of a small quantity of water (generally onto the surface of the material to be treated may require longer exposure times. This additional water can be applied as a fine mist in the case of relatively impervious products such as peppercorns or, preferably, by steaming in more difficult applications.

While particularly suited to use with water soluble volatiles, the method of the invention may also be used with other applications such as those requiring the transfer t 1 C~ I- -8of volatile substances that are soluble in, for example, lipids or other organic or inorganic solvents other than water (eg. some anti-oxidants).

Some post-contamination protection is also offered by the method of the invention and thus mechanical and/or human double handling is feasible. It is, however, preferable that where surface acidulation has been decreased to minimise acidic flavour effects, sometimes a requirement with bland materials, the material be handled and packaged in a manner so as to minimise microbial contarnination.

The method of the invention may also be performed in combination with one or more treatments of the material in accordance with the method described in copending 10 Australian patent application No. 75449/96. That is, the method of the invention may be performed in combination with one or more supplementary treatments involving evacuation of the vessel containing the material prior to contacting the material with a volatile substance entrained in a carrier gas. Such supplementary treatment(s) may be conducted prior and/or following treatment of the material in accordance with the 15 method of the present invention. The volatile substance used in the supplementary treatment(s) may be the same or different to the volatile substances used in the treatment(s) in accordance with the method of the invention. For some applications, the method of the invention may be performed in cycles with such supplementary treatments. Additionally, the volatile substance used in the separate cycles may vary or 1* 20 remain the same. The supplementary treatment(s) may be performed in the same vessel to that in which the material is treated in accordance with the method of the invention, or the supplementary treatment(s) in a separate vessel(s). In either case, the means for evacuating the vessel(s) is preferably provided by an external vacuum source. The Sevacuation is preferably conducted rapidly to achieve a sub-ambient pressure.

In addition, the inventors have found that it can be advantageous to dip or spray the material in'with a solution of the volatile substance, preferably prior to contacting the material with the volatile substance/carrier gas mixture. Dipping may be readily achieved by, for example, passing a conveyor with the material through a tank of an aqueous solution of the volatile substance. Following dipping, the material may then ~n Ilr be conveyed to a suitable vessel for treatment with a volatile substance/carrier gas mixture in accordance with the method of the invention.

The invention will hereinafter be further described by way of reference to the following, non-limiting examples and accompanying figures.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES: Figure 1 provides a schematic representation of a continuous treatment apparatus according to the invention, wherein the material is fed to a commercially available packaging machine for treatment and contacted with a volatile substance/carrier gas mixture provided through a gas sparging head.

S 10 Figure 2 provides a schematic representation of an alternative continuous S, treatment apparatus according to the invention. wherein a treatment vessel is isolated by rotary vacuum locks providing supplementary treatment stages.

s" Figure 3 provides a schematic representation of a further alternative continuous apparatus according to the invention, wherein the material falls in counter-current flow 15 to a volatile substance/carrier gas mixture.

MODE(S) FOR CARRYING OUT THE INVENTION As shown in Figure 1, continuous treatment of materials in accordance with the method of the invention may be achieved through a dedicated treatment system or commercially available packaging machine equipped with a conveyor a gas 20 sparging head and a gas control system Connected to the gas sparging head (3) by means of lines and and valves (10) and (11) is a compressed gas source one or more volatile substance sources preferably sparging vessels, and an aerosol trap The aerosol trap (14) is intended to minimise large droplets of the volatile(s) which can cause undesirable spotting and non-uniform distribution of the volatile(s) on the material surface. Multiple volatile substance sources (13) may be used to assist complete saturation of the carrier gas.

In the case of treatment with carbonic acid, the volatile substance source (13) may be at least initially filled with purified water such that bubbling of the CO, gas therethrough produces carbonic acid thus causing the CO, carrier gas to be at least partially satmated with the produced carbonic acid. Some materials will benefit more z after the carrier gas, preferably food grade carbon dioxide, has been passed through multiple volatile sources solvents to achieve a mixture of volatiles in the carrier gas.

Various type, combinations and concentrations of saturated carrier gases may be used to treat the material to optimise shelf-life and flavour parameters, particularly various mixtures of acetic and carbonic acids and hydrogen peroxide. A multiple volatile substance/carrier gas mixture may be provided by mixing a group of parallel preferred volatile substance/carrier gas mixture streams after passing through their respective volatile substance sources or, alternatively, a single carrier gas stream may be passed through a series of volatile substance sources.

10 In use, a batch ofmaterial (15) to be treated is introduced to a commercially available packaging machine The carrier gas is forwarded from the compressed gas source (12) to the volatile substance source the volatile substance thereby becoming entrained in the carrier gas, which is then introduced into the packaging machine through gas sparging head to thereby contact the material Valves 15 (16) and (17) may be operated to bypass the additional volatile substance source (13) if only one volatile substance source is required. The carrier gas, which is at least partially stripped of the volatile substances, is allowed to escape through a pressure regulator valve achieving a desired process overpressure for the desired contact time.

The duration of contact between the material and the volatile substance/carrier 20 gas mixture may be optimised to provide the maximum reduction in microbial bioburden while achieving the desired flavour and other properties of the material being treated. Once the desired duration of contact is attained, the flow of carrier gas is ceased and the pressure regulating valve released. The treated material is then removed from the vessel and packaged As shown in Figure 2, an alternative continuous treatment of materials in accordance with the method of the invention is achieved through a dedicated treatment system wherein material (23) is fed to a first rotary vacuum lock (24) (or other effective cavity mechanism) then. in trnm to conveyor (25) within treatment vessel (26) where the material is contacted with a volatile substance/carrier gas mixture, provided through gas sparging heads without prior evacuation of the treatment vessel (26) i 'I -llin accordance with the method of the invention. From the conveyor, the treatment material is transferred to a collecting hopper (28) via a second rotary vacuum lock (29) (or other effective cavity mechanism). The first and second rotary vacuum locks (24) and (29) isolate the vessel and permit operation of a two or three stage process wherein the material is also treated within the first and/or second rotary vacuum locks (24) and (29) with supplemental treatment(s) involving contacting the material with a volatile substance/carrier gas mixture preferably following evacuation The stage performed in the treatment vessel (26) may be of considerably longer duration than either or both of the supplementary treatment(s) and may benefit from cost !0 efficiencies associated with carrier gas recycling. Each of the stages could use the same -or different volatile substances.

As shown in Figure 3, continuous treatment of materials in accordance with the method of the invention may also be achieved through a dedicated treatment system, equipped with a means (31) such as an infeed hopper to deliver material (32) through a 15 suitable valve (33) (or conveyor) to the top of a vertical vessel (34) provided with one or more gas sparging heads (35) and material outlet valve (36) (or conveyor) located *within the base. A collecting hopper (37) is provided adjacent material outlet valve The gas sparging head(s) may be connected to a gas control system and sources of compressed carrier gas and one or more volatile substances in a manner as described above in connection to Figure 1. The material (32) passes through the vessel to the material outlet valve preferably in counter-current flow to the volatile substance entrained in the carrier gas. The carrier gas may be removed from the top of the vessel (34) through pressure regulator valve (38) and flue (39) and recycled if desired.

Residence time of the material within the vessel may be varied by adjusting flow rate of the material (32) and/or volatile substance/carrier gas mixture and/or by adjusting vessel (34) height so as to achieve a desired duration of contact between the material and volatile substancecarrier gas mixture or, alternatively, by interposing a screw conveyor system within the vessel with variable rotating speed to control the passage of the material (32) as it passes through the vessel In this configuration, the vessel

I.

,I

-12- (34) need not be erected vertically but can be arranged in any position compatible with the angle of repose dictated by the material (32) being treated.

Continuous treatment as shown in Figure 3 may be particularly suitable for grated/shredded cheese, other particulates and leafy materials such as herbs.

Example 1: TREATMENT OF SHREDDED CHEESE In this example, shredded cheese was placed in an evacuable test vessel and exposed to a acetic acidICO, gas mixture for the designated period(s) (ie. 2 x seconds with prior evacuation; 1 x 15 seconds without prior evacuation) with or I without prior evacuation of the vessel. The shredded cheese was contained in plastic 10 bags and a degree of pressure was allowed to develop in the plastic bags during eatment. The majority of the gas mixture entering the vessel escaped with approximately 50% of the residual gas mixture being expelled manually prior to sealing of the plastic bags. The samples were then stored for approximately twenty four hours prior to microbiological analysis. The results are provided in Table 1.

15 As can be seen from Table 1, a substantial reduction in the microbial bioburden of the shredded cheese was achieved both with and without the assistance of evacuation S. prior to contact with the acetic acid/CO 2 gas mixture.

Example 2: TREATMENT OF FRUIT WITH CARBONIC ACID DIPPING In this example, a twenty gram piece of skinned mango was dipped into an 20 equilibrated aqueous solution of carbonic acid for ninety seconds while a continual supply of food grade carbon dioxide was bubbled through the solution in an attempt to maintain an excess concentration of carbonic acid. The mango piece was treated with volatile carbonic acid in CO 2 carrier gas and held in this gaseous atmosphere at approximately 5°C for ten minutes whilst the aqueous carbonic acid dipping solution equilibrated (pH 4.0 by paper). Following re-dipping of the mango piece for one hundred and eighty seconds, excess water was removed by shaking.

Control and treated samples were stored under identical conditions at approximately 5 0 C. After three hours the control developed a dark orange colour and syneresis at three days. After three weeks there was very little change in the treated sample. Furthermore. only a slight amount of syneresis was observed after an additional rr ig, k' Ite irrr~-rciai-mar~

I

13- 24 hour storage time (ie. total 3 weeks and I day) at ambient temperatures. No change in colour nor observable mould growth was seen.

In similar trials with avocado, shelf-life was extended from three hours to sixty six hours; the assessment parameters again being colour and observable mould growth.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Ir r r 1 1<i h r "BP9 e~ T C TABLE I Total. Yeast FOODSTUFF GAS MIX No. of FLOW EXP. Plate Reduction Mould Reduction FLUSH RATE SEC. Count Count SHREDDED CONTROL CONTROL CONTROL CONTROL 3.61 E+05 CONTROL 5.87E+05 CONTROL

CHEESEI

CONTROL 4.56E+05 CONTROL 7.80E+05 CONTROL 1.19E+05 CONTROL S. 16E405 CONTROL Mean 3.45E+05 CONTROL 7.28E+05 CONTROL SHREDDED ACETIC

CHEESE

VACUUMIFLUSH

Sampl WVt: lflgms Aw 0.96 2 22L/M 1t] <10 V99.999 8.OOE±00 99.9989 SHREDDED ACETIC CHEESE 1 NO VACUUM Sample Wt~ logms Awv 0.86 22a1M 15 <10 1>99.999 1 10 >99.999

Claims (31)

1. A method of treating a material, comprising the step of contacting the material with a volatile substance entrained in a carrier gas.

2. A method according to claim 1, wherein the volatile substance is microbicidal.

3. A method according to claim 2, wherein the volatile substance includes a natural food acid.

4. A method according to claim 3, wherein the volatile substance includes carbonic acid. A method according to claim 2 or 3, wherein the volatile substance includes "10 acetic acid.

S.

6. A method according to any one of the preceding claims, wherein the volatile substance includes hydrogen peroxide.

7. A method according to claim 2, wherein the volatile substance is selected from the group consisting of carbonic acid, acetic acid, hydrogen peroxide and mixtures of carbonic acid and acetic acid, and carbonic acid and/or acetic acid with hydrogen peroxide.

8. A method according to any one of the preceding claims, wherein the volatile substance is entrained in the carrier gas by passing the carrier gas through a vessel containing the volatile substance.

9. A method according to any one of the preceding claims, wherein the volatile substance is prepackaged with the carrier gas.

A method according to any one of the preceding claims, wherein the volatile substance is entrained in the carrier gas in saturating amounts.

11. A method according to any one of the preceding claims, wherein the carrier gas is carbon dioxide and/or nitrogen gas.

12. A method according to any one of the preceding claims, wherein the method is conducted either batch-wise or continuously.

13. A method according to any one of the preceding claims, wherein the duration of the step of contacting the material with the volatile substance entrained in a carrier gas is in the range of 0.05 to 2 minutes. -T P i -16-

14. A method according to any one of the preceding claims, wherein the duration of the step of contacting the material with the volatile substance entrained in a carrier gas is in the range of 0.15 to 0.5 minutes.

A method according to any one of the preceding claims, wherein prior to the step of contacting the material with the volatile substance entrained in a carrier gas, the surface of the material is wetted with up to about 2.0% w/w of water.

16. A method according to any one of the preceding claims, wherein prior to the step of contacting the material with the volatile substance entrained in a carrier gas, an aqueous solution of a volatile substance which may be the same or different to the first- S' 10 mentioned volatile substance is applied to the surface of the material.

17. A method according to claim 16, wherein the aqueous solution is applied to the surface of the material by dipping or spraying.

18. A method according to any one of the preceding claims, wherein the step of contacting the material with a volatile substance entrained in a carrier gas is conducted 15 in a vessel with an over-pressure of up to 3 bar (2250mm Hg) above atmospheric pressure.

19. A method according to any one of the preceding claims, wherein the step of contacting the material with the volatile substance entrained in a carrier gas is repeated up to 3 times.

20. A method according to claim 19, wherein each step of contacting the material with the volatile substance entrained in a carrier gas is conducted in separate vessels.

21. A method according to claim 19, wherein each step of contacting the material with the volatile substance entrained in a carrier gas is conducted is conducted in a single vessel.

22. A method according to claim 21, wherein between each step of contacting the material with the volatile substance in a carrier gas, the vessel is evacuated and/or flushed with a suitable gas.

23. A method according to any one of the preceding claims, wherein the material to be treated is a food, pharmaceutical product or ingredient thereof.

24. An apparatus for treating a material comprising: -17- a vessel for containing the material; means for entraining a volatile substance in a carrier gas; and means for contacting the material contained within the vessel with the volatile substance entrained in the carrier gas.

25. An apparatus according to claim 24, wherein the means for entraining the volatile substance in the carrier gas is provided by a compressed gas source in communication with a volatile source.

26. An apparatus according to claim 24 or 25, wherein the means for contacting the material contained within the vessel with the volatile substance entrained in the carrier gas comprises a sparger.

27. An apparatus according to any one of claims 24 to 26, further comprising a means for tumbling the material within the vessel.

S.28. An apparatus according to any one of claims 24 to 26, wherein the apparatus is arranged such that the material passes through the vessel in counter-current flow to a flow of the volatile substance entrained in a carrier gas.

29. An apparatus according to any one of claims 24 to 28, further comprising a conveyor for continuously conveying the material into the vessel.

An apparatus according to any one of claims 24 to 29, further comprising means for feeding the volatile substance entrained in a carrier gas to the vessel to achieve an S 20 over-pressure of up to 3 bar 2 2 50mm Hg) above atmospheric pressure.

31. An apparatus according to any one of claims 24 to 30, further comprising means for contacting the material with an aqueous solution of a volatile substance which may be the same or different to the first mentioned volatile substance. DATED this 20th day of August 1998 DAVID JAMES LARK and ANDREW STIRLING INGLIS Attorney: PAUL G HARRISON Fellow Institute of Patent Attorneys of Australia of BALDWIN SHELSTON WATERS i