REDUCED SALT PRESERVATION PROCESS FOR SKINS AND HIDES

Technical Field

The present invention relates to a process which reduces or eliminates the need to use sodium chloride to preserve skins or hides.

Background Art

When an animal is slaughtered at an abattoir the skin is removed and preserved then sold, normally to tanners. The preservation process is required to allow storage and/or the transportation of the skin without the skin deteriorating. Properly preserved skins are expected to have a shelf life of at least 4 months without any deterioration

There are a variety of preservation methods available including cooling, freezing, drying, salting (dry or wet) or brining for skins and hides, and various chemical treatments.

The cost of freezing is expensive and not in common use industrially.

The drying of skins or hides can be economical if the drying can be carried out naturally, for example in countries such as India, Australia, Africa and South America but it can be time consuming. As some of the dry processing is carried out in the open insecticides may need to be added and these can be problematic to the downstream processing. It should be noted that straight drying is not the preferred method of preservation because any over or under drying can cause serious problems for the tanner.

The most commonly used preservation processes use common salt (sodium chloride) with the addition of biocides and/or fungicides. In countries like New Zealand the skins are normally washed then dewatered, usually mechanically, and if necessary trimmed of flesh and fat prior to drumming with a salting mixture. Other countries do not wash or flesh prior to further processing. The salting mixture is essentially sodium chloride with some biocides, with the mass of sodium chloride used being around 35% to 45% of the drained weight of the skins prior to processing. The processed skin retains a high concentration of sodium chloride which acts as a bactericide, the sodium chloride also removes water from the skin during the process. The New Zealand Ministry of Agriculture and Fisheries indicate that a properly cured skin should contain less than 50% water and be at least 85% saturated with salt. In many parts of Europe the skins are hand salted, onto the flesh side, then often chilled. This processing when properly carried out, and the skins are kept in cool dry conditions, preserves the skin for at least 6 months.

The salting mixtures and preservation methods used by each country varies, and each processing plant within those countries will have their own variations within this. For example in New Zealand drumming or mixing with 35% to 45% the drained weight of skins of a salting mixture containing 1-2% boric acid or citric acid and 0.2% dichlorophen, based on the weight of salt, is common.

Typically in Australia the skins are drummed with a salting mixture containing 1 % boric acid and 1 % sodium fluoride, by weight, approximately 2.2kg of the salting mixture is used per skin. In Europe the skins are hand salted and stacked with around 1 kg salt mixture per skin used. In most cases sodium chloride is the major constituent of the salting mixture, although some potassium chloride can be substituted albeit with a higher cost. For hides the drum or mixer based process involves processing with a salt mixture at the saturation limit for sodium chloride for at least 8 hours, hand salting requires 12 to 20kg salt per hide and many days stacked to drain and age.

When the salted skins or hides are received by a tannery they need to be washed to remove the sodium chloride. Typically during washing around 2kg of sodium chloride is removed from each sheepskin and around 15kg from a hide. Given a large tannery can process 50,000 skins per day this results in 100 tonnes of sodium chloride being washed out of the skins per day. This sodium chloride needs to be disposed of or recovered. Most tannery effluent is monitored for one or more of the following: BOD (Biological Oxygen Demand), COD (Chemical Oxygen Demand), colour, odour, SS (suspended solids), Nitrogen and pH. Before discharge to a water course tannery effluent must be treated, either onsite or at municipal sewerage works, and required to meet local standards.

This effluent treatment can include balancing, screening, settlement and biological treatment. During treatment the COD, SS, BOD, etc are substantially reduced but unless dilution is part of the treatment these have little effect on the sodium chloride present. For this reason larger tanneries can release 50 tonnes/day (or more) of sodium chloride into rivers or the municipal treatment system which can have a detrimental impact on water courses and lakes or the operation of treatment plants. For example in China where some of the rivers provide drinking water this additional salt can make the water unusable for this purpose.

It is possible to remove or at least significantly reduce the sodium chloride, and any other dissolved solids, from the waste water by a variety of means such as membrane filtration, ion exchange or drying for example, but each of these has a potentially high cost and as such they are not often used.

It should also be noted that the abattoirs are unlikely to adopt a method of preserving the skins or hides produced that does not fit within their current processing regime unless it is dictated by their customers, lower in cost, and/or required to meet local government standards or laws. The industry is also slow to change unless regulation forces it.

Certain preservation methods use boric acid and this is becoming less acceptable, in fact some tanners are refusing to accept preserved skins which contain boric acid.

Any discussion of the prior art throughout the specification is not an admission that such prior art is widely known or forms part of the common general knowledge in the field.

It is an object of this invention to provide a process which reduces the amount of sodium chloride that is used to preserve a skin or hide, or provide the consumer with a useful choice.

Disclosure of Invention

The present invention provides a skin or hide preservation process that is an essentially dry process for preserving animal skins or hides that includes the following steps, in order:

A. determine a water content of primary skins to be processed;

D. process primary skins with a predetermined quantity of a dry preservation mixture to create processed skins;

such that the dry preservation mixture includes: at least one solid acid with a melting point above 20°C; and a salt mixture containing sodium chloride and/or potassium chloride, with the potassium chloride concentration between 0% and 100%;

where the mass of the at least one solid acid added results in a pelt pH of 3.5 or below and the mass of salt mixture added results in a minimum concentration of

50g salt mixture/ litre of water within the processed skin.

Preferably the dry preservation mixture is in a divided form. Preferably the divided form is pellets, granules, powder, crystals or a combination of these forms.

In a highly preferred form the mass of the at least one solid acid is at least 3% of the mass of the primary skins. Preferably at least 10% salt mixture by mass of primary skins is added. Preferably the at least one solid acid has a melting point above 30°C. In a more preferred form the melting point of the or each solid acid is between 30°C and 45°C.

Preferably the at least one solid acid is one or more acid selected from the list consisting of oxalic acid, benzoic acid, sulphamic acid, sodium hydrogen sulphate (NaHS0 ₄ ), potassium hydrogen sulphate (KHS0 ₄ ), malonic acid, fumaric acid, tartaric acid, citric acid, and monochloroacetic acid.

Preferably the dry preservation mixture includes a fungicide and/or biocide. In a highly preferred form the dry preservation mixture includes more than one fungicide or biocide. Preferably the dry preservation mixture contains at least 0.05% of any one biocide or fungicide. In a highly preferred form the dry preservation mixture contains at least 0.1 % of any one biocide or fungicide. Preferably the fungicide and/or biocide is one or more species independently selected from the list consisting of p-chloro-m- cresol, o-phenyl-phenol, carbendiazim, chloroxy-xylenol, sodium pyrithione, di- iodomethyl-p-tolyl-sulphone, 3-iodo-2-propynyl-N-butylcarbamate, 2,2-dibromo-3- nitrilopropionamide and dichlorophen.

Preferably between step A and step D there is a step C where step C is

C. add primary skins to process vessel; Preferably in an alternative form the process is carried out by hand. In one preferred form the process is carried out by direct application of the dry preservation mixture to the primary skins which are then stacked.

Preferably the process vessel is used to process the primary skins into processed skins.

In a preferred form the dry preservation mixture contains at least one solid acid which is in crystalline, granular or powdered form, where a solid acid is an acid that has a melting point higher than about 30°C, and preferably higher than 45°C.

In a highly preferred form the dry preservation mixture includes:

at least one solid acid;

sufficient potassium chloride or sodium chloride to maintain a minimum concentration of 50 to 70 g/litre of any water present; and

one or more biocide or fungicide;

all in crystalline, granular or powdered form, where a solid acid is an acid that has a melting point higher than about 30°C, and preferably higher than 45°C.

In a highly preferred form the or each acid is selected from the list consisting of sulphamic acid, sodium hydrogen sulphate potassium hydrogen sulphate, lactic acid, malonic acid, fumaric acid, tartaric acid, citric acid, monochloroacetic acid and oxalic acid. In a still more preferred form the acid is oxalic acid, preferably as a dihydrate. Preferably during processing small amounts of additional solid acid are added to maintain the pH within a predetermined range.

In a highly preferred form the dry preservation mixture is added as a One shot' dose to the process vessel.

Preferably after step A the water content is adjusted to a predetermined level.

The present invention also includes any skins or hides prepared by the process described. The present invention also includes a dry preservation mixture for skins or hides that includes at least one solid acid and a salt mixture where the at least one solid acid has a melting point above 20°C; and the salt mixture contains sodium chloride and/or potassium chloride, with the potassium chloride concentration between 0% and 100%.

Preferably the dry preservation mixture is as described in the process description above.

Brief Description of Drawings

By way of example only, a preferred embodiment of the present invention is described in detail below with reference to the accompanying drawings, in which:

Figure 1 is a flowchart of the process;

Figure 2 is a flowchart of an alternative process;

Definitions:

Hydro, or hvdroed refers to centrifuging washed skins to remove the water, additional steps may follow the centrifuge dewatering stage.

Offer: amount of preservation mixture, or individual component of that preservation mixture, added as a percentage of the weight of skins or hides to be processed, basically the amount of material offered to process those skins/hides.

Raw Skin: skin or hide as removed from the animal.

Salt: When used herein this is intended to mean common salt or sodium chloride. Salt Mixture: when used herein, this is a mixture of sodium chloride and/or potassium chloride with up to 20% additives, the potassium chloride concentration being between 0% and 100% of the mixture. That is the salt mixture is x% NaCI + (100-(x + y))% KCI + y% additives, where y is less than or equal to 20%, and 0%≤ x≤ 100%.

Skin: When used herein this is intended to cover skins of smaller animals such as sheep, deer and goats and hides from larger animals such as cattle.

Best Mode for Carrying Out the Invention

The process involves the treatment of raw or washed animal skins or hides with an essentially dry, acidic preservation mixture, that results in a preserved skin or hide with a significantly reduced quantity of sodium chloride (or potassium chloride when used) when compared to existing methods. The dry preservation mixture includes at least one solid acid which can, at the concentrations used, lower the pH in the skin to 3.5 or below at the time of processing.

Acid conditions, less than pH 2.5, prevent most commonly encountered bacteria but moulds and fungi may still proliferate, as such a fungicide and/or mould inhibitor will be necessary in many cases.

Referring to Figure 1 the process is shown as a flowchart with the following steps in order:

A. determine a water content of primary skins to be processed;

B. add dry preservation mixture;

C. add primary skins to process vessel;

D. process primary skins to create processed skins.

Where step C is optional. Step C will not be present for most hand salting operations, and may not be present for those operations where low labour costs make manual processing economical.

Prior to step A the raw skins just removed from the animals are washed to cool the skins and remove any surface contaminants or loose material. This washed skin is then dewatered by known means, usually by putting through a mangle or hydro. After dewatering the washed skin typically retains around 120% the dry weight of the skin as water. In addition it has been found preferable to lightly shape the skin or hide to be processed by removing long or tubular shanks, anus holes or pizzles. This preprocessing step results in a primary skin which proceeds to step A.

It should be noted that not all processing plants wash the raw skins, and others may remove different amounts of water from the washed raw skins by using hydro or mangle. Where the water content of the ex-processing plant skins is too low it may be necessary to add water to the raw or washed skins to create primary skins with sufficient water. In some cases the raw skin may be the primary skin.

Please note that the term 'essentially dry process' is intended to mean the process is not carried out in an aqueous bath. In step A the primary skins are weighed before and after washing to determine the wet weight which allows the free water content of the primary skins to be determined. This free water content is then used to determine the composition and/or the mass of the dry preservation mixture to be used. This method of weighing ignores any water present within the skin prior to washing which may be up to 75%.

Using the water content of the primary skins, the composition and quantity of the dry preservation mixture is determined. It is believed that the water content of the primary skins should be close (+/-30%) to 100% the dry weight of the primary skins for optimum processing, but the range for successful processing is yet to be fully explored. It is believed that the water content (on a dry basis) for successful processing should be in the range of 50% to 250%. On a wet basis the water content is expected to be in the range 25% to 75%.

It should be noted that the determination of the water content may be a formal determination or simply be counting the number of primary skins and using a table to estimate the water content.

In further cases the determination of the water content is merely counting or weighing the primary skins and using this count or skin mass, along with properties of the primary skins to determine the mass of dry preservation mix to use. In this case the 'properties of the primary skins' includes, how the raw skins have been processed to produce the primary skins prior to the preservation process, for example:

(a) washed; or

(b) washed and mangled; or

(c) washed and hydroed; or

(d) flayed raw skin;

and, the age of the animal, size of the skin, wool length or any other physical characteristics of the primary skin. The mass of dry preservation mixture used is therefore based on the 'known' or 'estimated' water content of primary skins based on those properties. Knowing the properties of the primary skins allows the water content to be estimated without direct measurement. This indirect determination of water content, where the actual water content is not directly calculated or directly noted, is intended to be covered when 'determine the water content of the primary skins' is used. For example knowing you are processing 200 washed and hydroed lambskins with 1 "(25.4mm) of wool determines the water content of the primary skins. In step B the dry preservation mixture is prepared, this may be carried out by adding the individual ingredients to a process vessel, but in some circumstances it will not be prepared in the process vessel and may even be premixed. When used for a manual process the ingredients of the dry preservation mixture may be prepared in a mixer from the raw materials prior to application or supplied premixed from an external source.

It is believed that the dry preservation mixture should contain at least:

one solid acid;

sufficient potassium chloride or sodium chloride to maintain a minimum concentration of 50 to 70 g/litre of any water present; and

one or more mould inhibitor, biocide or fungicide;

all in crystalline, granular, flake or powdered (i.e. solid) form. In addition to the active ingredients a solid dispersant may be needed to ensure the even distribution of the solid acid and fungicides.

The solid acid preferred is oxalic acid but any solid acid for example sulphamic acid, sodium hydrogen sulphate (NaHS0 ₄ ), potassium hydrogen sulphate (KHS0 ₄ ), lactic acid, malonic acid, fumaric acid, tartaric acid, citric acid, monochloroacetic acid or similar that are able to maintain the skin pH below about 3.5 have been found successful in trials so far. Solid acids such as benzoic acid are being trialled but they are weak acids with a low solubility and it is likely that they will be used in combination with more soluble solid acids. It is essential that the acid is a solid at room temperature, so acids like lactic acid (liquid at 18°C) are not believed to be suitable. It should be noted that room temperature may mean 6 to 10°C or 30°C or any temperature in between depending on the location. For skins with low water contents, for example unwashed skins, it is felt that a solid acid mixture which includes highly soluble solid acids such as citric acid will be necessary.

It is believed that the solid acid should be capable of creating an aqueous solution with a pH of less than 3.5 to reduce the likelihood of moulds or bacteria. In some cases the solid acid should have limited solubility in water so that free crystals remain after processing, in this case acids like oxalic acid and sulphamic acid appear most suitable. Though the amino group on sulphamic acid may provide a food source for certain fungi so it may need to be augmented by additional fungicides. This being said where the skin has a low water content, below about 60%, a mixture containing soluble acids such as citric acid and low solubility acids such as oxalic acid may be necessary.

The sodium chloride or potassium chloride concentration is required to minimise or eliminate any swelling of the skin or hide being processed. Recent trials have shown that an offer of 20% salt and 5% Oxalic acid with a suitable fungicide results in a uniform distribution of the preservation mixture When processing a sheepskin it is expected that this will result in less than 400g of sodium chloride and less than 400g of potassium chloride being retained by a typical sheepskin after preservation. This amount of retained sodium or potassium chloride is much less than current levels, which is typically 1800g. The use of potassium chloride rather than sodium chloride, or a mixture of the two does work but the potassium chloride in many cases must be the sterilised (normally heat sterilised) form. The use of potassium rather than sodium chloride for processing will be dependent on the cost and as such will depend on the location and is likely to change over time.

The addition of one or more biocide or fungicide is optional, that is it may not be necessary as in some compositions of the dry preservation the solid acid used may eliminate this requirement. However, for certain applications, up to 10 g of sodium fluoride or 15 g of sodium hexafluorosilicate per kg wet weight of skin along and/or specific biocides, mould inhibitors or fungicides may be added. Like the use of boric acid, the use of fluoride salts may well be phased out due to health and safety concerns. Once again all of the biocides and/or fungicides are added as solid compounds and must be soluble (even if to a limited extent) in water. Some examples of acceptable compounds are p-chloro-m-cresol, o-phenyl-phenol, carbendiazim, dichlorophen, chloroxy-xylenol, sodium pyrithione, di-iodomethyl-p-tolyl-sulphone, 3- iodo-2-propynyl-N-butylcarbamate, and 2,2-dibromo-3-nitrilopropionamide.

The cost and potential toxicity of the specific biocides and/or fungicides necessitates their use in low quantities, usually below 0.1 % of the skin weight. This has led to the consideration of compounds that are insoluble or have a low solubility in water, these would be in the form of a sol, a colloidal suspension or similar. One fungicide/bacteriocide found suitable is colloidal sulphur. In trials using 2% to 4% colloidal sulphur to replace part of the salt in the preservation mixture significantly increased protection from fungal attack, examples with colloidal sulphur used and the stability test results is provided in the examples. It has been noted that for certain applications the colloidal sulphur can impart a slight yellow tinge.

Due to the low cost of colloidal sulphur it is believed that higher concentrations can be used, possibly 5% or more. It is believed that the use of colloidal sulphur will result in:-

1. Better fungicidal protection, due to the increased concentration;

2. More uniform distribution of acid and fungicides; and

3. The partial replacement of NaCI or KCI, leading to a reduction of these species in any effluent discharges.

As sulphur is insoluble in water it is believed there will be minimum effect on the chemical loading of any effluent streams.

It should be noted that there is a tendency for higher levels of sulphur to yellow the wool which is undesirable for many end uses, as such only low concentrations may be able to be used. Benzoic acid is a weak acid which has good fungicidal properties and it may offer an alternative to sulphur.

To reduce the amount of sodium chloride present further, but still ensure that the fungicides/biocides are evenly distributed amongst the skins the addition of a solid dispersant may be necessary. Where the addition of a solid dispersant is required it is believed that this must meet the following criteria:- a. Be essentially insoluble in water; and

b. It must not include any "heavy metal" elements; and

c. It must result in no permanent colouration.

Some suitable examples of solid dispersants meeting these criteria are silicon dioxide, bentonites, zeolites and silica gel, wood pellets or diatomaceous earth may also be an acceptable alternative. It was proposed in "Liricure" in JSLTC 81 , [1997] 137-143 that medium coarse sawdust [pine] may be an acceptable alternative.

Each of the components of the dry preservation mixture is added to the process vessel which is preferably a standard processing drum used for the processing of animal skins. The dry preservation mixture is then mixed in the processing vessel, as such the drum should be able to be rotated or incorporate some form of mixer. The contents are then mixed to ensure an even distribution of the ingredients through the dry preservation mixture.

Each of the various components of the dry preservation mixture may be in the form of powders, granules, flakes, crystals or any other suitable solid form. In addition the various components may be pre-coated or added in bags or other containers to control the concentration of the specific ingredient within the dry preservation mixture over time. In some forms some components may be encapsulated with a coating that breaks down over time within the process vessel, or added in a form which breaks down under physical action thus controlling the addition rate. In fact in some compositions a proportion of some active ingredients may be coated with a coating designed to break down.

In some cases the full quantity of dry preservation mix, or certain parts of the mix, are added during the processing rather than at the start. This allows some of the dry preservation mixture to be added/mixed prior to the skins being added with the rest added after the skins. This stepwise addition allows the skins to be contacted with a first chemical/mixture and then a subsequent chemical/mixture, which allows for a chemical reaction between first and subsequent chemical/mixtures, maintenance of the concentration of specific ingredients, the adjustment of the second/subsequent addition quantity or any combination of these.

Where step C is present the following steps apply.

Once the dry preservation mixture is at the required level of consistency step C is undertaken. In step C the primary skins are added to the process vessel then the dry preservation mixture is added, and step D is undertaken. It should be noted that a proportion of the dry preservation mixture can be added prior to, or with, the primary skins, with the remainder added after the primary skins are present.

In step D the primary skins are mixed with the dry preservation mixture and processing undertaken, during processing the drum is rotated to mix the dry preservation mixture and primary skins. The processing is continued until the desired penetration of dry preservation mixture into the primary skins is achieved, at a pH below about 3.5. In some instances it is thought that additional solid acid (and possibly other ingredients) may need to be added during processing in some cases to maintain the pH below about 3.5. Trials thus far have not shown this to be necessary but in certain environments some additions may be needed.

Once the processing is complete there will be an acceptable level of acid, biocide and fungicide within the skin that is sufficient to preserve the skin during storage and transport. Once this acceptable level is achieved the primary skins can be considered processed skins. It is expected that this desired penetration will occur after about 70 to 90 minutes processing at 4rpm to 8rpm for sheepskins and around 8 hours for hides. It is expected that a solid acid will be an acid that has a melting point higher than about 30°C, and preferably higher than 45°C.

Where step C is not present step D the primary skins have the dry preservation mixture applied manually, as uniformly as possible, and they are then stacked flat to process and drain. The processing is continued until the desired penetration of dry preservation mixture into the primary skins is achieved, at a pH below about 3.5. In some instances it is thought that additional solid acid (and possibly other ingredients) may need to be added during processing in some cases to maintain the pH below 3.5. Trials thus far have not shown this to be necessary but in certain environments some additions may be needed.

One method of determining the end point of processing is monitoring the pH, when the pH reaches a plateau, or no addition of solid acid is required to maintain the pH for a predetermined time, then the process is complete and the primary skins are now processed skins. Alternatively the end point may be simply when the pH reaches a preset value, and this could be determined by an indicator within the dry preservation mixture or sampling. For example immersion of a preset amount of processed skin could be immersed in a predetermined amount of deionised water and the pH and/or chloride level determined by any known means (e.g. pH meter, indicator, conductivity, titration, etc). One method involves using a suitable indicator such as thymol blue on a cut section of the skin/hide.

It is believed that as trials are carried out other methods of determining the end point will also be found, for example a predetermined time period, the disappearance of an indicator, the determination of free biocide/fungicide present, etc. The processed skins are then removed from the processing vessel and stacked for storage and/or transportation. Preferably the processed skins are then stacked skin up, with the top skin hair or wool up then covered with a watertight plastic material. As is normal the processed skins should be stored in a cool area out of direct sunlight. Over time the solid acid will be consumed by the skins but it will maintain the pH in the range of 2 to 3.5 for an extended period. It should be noted that to minimise the chance of any swelling from condensation a small amount of salt may be added to the top skins.

In some embodiments the dry preservation mixture may be in bulk and step B is simply weighing out the correct amount for the batch of primary skins to be processed. In further embodiments it may be made up of preselected bulk and pre-packaged mixed ingredients. In other words step B may be:

taking the raw materials and blending or reacting them to create the dry preservation mixture, or

adding specific masses of pre-blended and/or raw materials together and mixing; or

counting pre-weighed bags of individual or premixed ingredients and mixing; or

adding a specific quantity or number of containers with premixed ingredients without forming a homogeneous dry preservation mixture first; or

any combination of the above; or

any other suitable means of preparing the dry preservation mixture.

The dry preservation mixture can be prepared as individual component parts, pre- blended ingredients, or as a one shot mixture. The individual components, pre- blended ingredients or one (single) shot mixture can be as pre-weighed units or bulk. Noting that the one shot mixture or pre-blended ingredients may contain separately packaged or formulated ingredients which allow for time delayed release of some or all of the specific components. The time delayed components may be in packaging designed to release their contents over a specific time, when there is a specific amount of free water present, when a specific pH or other predetermined condition is met. It is expected that the dry preservation mixture will be provided premixed in suitably sized bags and as such step B will merely be determining the number of bags to add. In some embodiments there may be a number of different sized bags, or be bags which contain different compositions, so that the dry preservation mixture can be tailored to specific batches of primary skins by adding a combination of premixed bags.

In some embodiments the preservation mixture is applied to the skins mechanically, automatically or at least not manually by hand, prior to the skins being stacked.

It is intended that the dry preservation mixture will be provided in granulated or pelletized form. The pellets and/or granulated forms have been produced with standard pelletizing/granulation equipment but the steps vary depending on the dry preservation mixture's composition. With very low melting point acids the pelletizing and granulating machinery can melt the acids, which changes the equipment that can be used. Pelletisation trials already completed have shown that the inclusion of potassium chloride in the mixes, particularly when dispersants such as zeolites are being used is beneficial to augment the formation of the pellets.

In an alternative form, as shown in Figure 2, the process involves the following steps in order:

A1. Determine a water content of primary skins to be processed;

D1. Process the primary skins with a predetermined quantity of a dry preservation mixture to create processed skins; where the dry preservation mixture includes at least one solid acid selected from the list consisting of oxalic acid, sulphamic acid, sodium hydrogen sulphate potassium hydrogen sulphate, lactic acid, malonic acid, fumaric acid, tartaric acid, citric acid, benzoic acid and monochloroacetic acid.

It should be noted that the determination of the water content may simply be counting the number of skins and using a table to estimate the water content. In further cases there may be no formal determination of the water content, the number of skins simply counted and step D1 undertaken as the first step using this count to determine the mass of dry preservation mix to use. As such step A1 is needed but may not involve a formal determination of the water content.

To provide the process in a more specific form it is expected that a typical batch process would be as follows:

200 washed and drained sheepskins (primary skins), typical weight 800kg (wet weight). The water content based on this weight is determined to be 400kg (50% on wet weight basis, 100% on dry weight basis).

The mass of dry preservation mixture to be added was determined to be 15% to 25% of the wet weight that is about 120kg to 200kg (excluding fungicide) for this 800kg of primary skins, made up as shown in Table 1.:

Table 1.

NaF is optional and where not present the other figures may change slightly and the oxalic acid is the dihydrate.

In fact as NaF is toxic it is preferable to keep the NaF no higher than 1 % and as such the offer drops slightly to about 14% and about 24% as shown in Table 2.

Table 2.

Once again the NaF is optional and where not present the other figures may change slightly.

The primary skins (raw skins washed and drained) are added to the drum and the ingredients of the dry preservation mixture are added. The drum is rotated at 4 - 8 rpm for 80 to 100 minutes, or until the pH falls to a constant value below pH 3.5. At present the best practise for meat processing works in New Zealand is 6rpm for 90 minutes. The skins are removed and flat on pallets with the pelt side uppermost and drained for a minimum of 24 hours. The now processed skins are folded down the backbone with the wool side outermost. These folded processed skins are then stacked uniformly with the top skins sprinkled with salt, the stacked skins are then wrapped with a plastic cover.

When the processed skins are received at the tannery the skins may require de- acidification before normal processing. For example if the skins are to have the wool removed in the usual fashion [flesh side of skins painted with highly alkaline paint containing sodium sulphide] it is essential that any residual Oxalic acid is neutralised.

After determining the actual amounts of residual Oxalic acid [by titration] present in the skins, sodium carbonate [10.6g sodium carbonate will neutralise 9g Oxalic acid] is added to the liquor and pre-dissolved before addition of skins. Deacidification in this way is expected to minimise any risks from acid swelling. The deacidification is a slow process and in order to ensure the grain layer is de-acidified trials have shown that an overnight soak may be necessary. Additions of small offers of hydrogen peroxide can be expected to increase the rate of Oxalic acid removal. The use of oxidase and decarboxylate enzymes are also likely to be suitable for oxalate/oxalic acid removal.

If the skins are to be processed as wool on skins it may be possible to process without the above de-acidification process.

The processing time and equipment used may differ from the normal operation of the abattoirs but there will be a dramatic reduction in the sodium chloride present in processed skins.

Oxalic Acid can be aggressive towards the materials used for some processing equipment, as such some or all of the oxalic acid can be replaced with sodium hydrogen sulphate. The pH of the treated skins is the most important factor and providing this is below about 3.5 the solid acid (or mixture of acids) used is less important.

It should be noted that the water content of the skins may be determined by assuming a 'known' quantity of water is normally retained by a skin with that particular preprocessing, as such the determination may simply be counting the skins and using this 'known' value. For example in New Zealand a washed and mangled skin, with one inch wool, is assumed to be on average 4kg, 1 kg pelt + 1.5kg wool, with a water mass of around 1.5 kg, an unwashed skin is assumed to be around 0.8kg or around 20% water. So using a 4kg figure, and knowing the number of skins, the amount of water present and thus the amount of preservative to add can be estimated by counting the number of skins, or simply weighing the total mass of skins and using a predetermined water content figure.

Actually measured figures for the water content for a 2 inch lambskin, sourced from New Zealand are given in table A below:

Table A - actual pelt, wool and water contents of 2 inch lambskins

In Australia the lambskins are larger and often have a higher residual fat and flesh remaining on the skins than New Zealand, as such, even though Australian skins are unwashed, an average mass of 5kg can be used.

Example 1.

All percentages are masses based on the determined wet weight of the primary skins:

For all of the recipes any suitable solid fungicide or biocide can be used.

In many cases the preservation mix is pre-mixed to form a bulk material such as the one in the following example

Bulk Mix #1

100Kg Sodium Chloride Grade 23 [kiln dried and sterilized]

100Kg Potassium Chloride 10 mesh [2.5mm] - kiln dried and sterilized

50Kg Oxalic Acid [dihydrate**] **actual content of 100% Oxalic = 71.4% or 35Kg 1 Kg Para Chloro Meta Cresol flakes [PCMC]

From further research it has been confirmed that 10% NaCI, 10% KCI, 5% Oxalic Acid and 0.2% Fungicide is successful, all figures being mass percentage on a wet skin basis.

Example 2.

Results from Oxalic acid trials using between 3% and 5% oxalic acid (as a dihydrate) to determine how quickly the oxalic acid is consumed are shown in Table (i):

Table (i).

The figures given for oxalic acid are for pure unhydrated H ₂ C ₂ 0 ₄ , the figures in square brackets [ ] are for oxalic acid dihydrate. Example 3.

To further confirm the effectiveness LASRA (New Zealand Leather and Shoe Research Association Incorporated) accelerated mould testing and storage testing was carried out and the results are shown in table (ii) below. The solid preservation mix for these trials consists of 20% sodium chloride + [% indicated in Table (ii)] Acid + [percentage and composition indicated in Table (ii)] fungicides. For example for T-10 20% sodium chloride + 2% citric Acid + 0.1 % o-phenyl-phenol was added. All percentages are masses based on the determined wet weight of the primary skins:

For T-99 10% sodium chloride and 10% unsterilized potassium chloride was used, and for T-88 only 10% sodium chloride (rather than 20%) was used, the rest use 20% sodium chloride.

For this series of tests samples were sent to LASRA (New Zealand Leather and Shoe Research Association Incorporated) accelerated mould test procedure. This test involves inoculating disc samples of the treated skins with 15 known moulds followed by incubation at 25°C and 100% relative humidity. Samples fail when evidence of mould is found and the Days To Fail Mould Test [DTFMT] is recorded. This is a very aggressive test. Samples were taken from 3 skins in each trial. A Neck sample was taken from skin 1 , a Flank sample was taken from skin 2 and a Butt sample was taken from skin 3. Each sample was tested in duplicate. In addition a storage trial was carried out using the 6 trial lots processed as indicated, which were then stored in a container and maintained at 25°C. This additional trial attempts to simulate storage in warm climates, the results, after storage for 105 days, are in the column titled PSSM (Percentage Skins Showing Mould).

Table (ii).

Where PCMC = p-chloro-m-cresol, OPP = o-phenyl-phenol and DCPN = Dichorophen

The control (industry standard) did not fare well with the container test.

T-22 gave very good results.

T-9 gave mixed results with good container results.

T-99 and T-88 gave poor LASRA results but good container test results

T-1-4 gave poor LASRA results, thought to be related to the reduction in fungicide as the container test was good. Example 4.

During the trial carried out in example 3 the pH within the skin and wool was measured and the results are presented in Table (iii).

Table (iii).

P = Pelt; W = Wool

Example 5.

Details of a bulk trial carried out in a New Zealand freezing works are shown in Table (iv).

Table (iv).

Where PCMC = p-chloro-m-cresol, OPP = o-phenyl-phenol and DCPN = Dichorophen Sodium chloride was used as no suitable sterilised potassium chloride could be sou reed.

The % figures given are approximate, for example 20% sodium chloride is in fact 127kg not 130kg or 21 %.

The latest LASRA Intensive mould test procedure results from the bulk trial are below: Control

Samples from 3 separate skins tested in duplicate. One set of samples failed after 28 days, the other two sets have not failed after 56 days. Result: 33% failure rate at 28 days.

Trial Mixture

Samples from 4 separate skins tested in duplicate, after 56 days no failures have been recorded.

Example 6.

Trials with Australian sourced skins has shown that the quality of flaying can affect the penetration of the dry preservation mixture, the flesh and fat remaining on the skins preventing direct contact with the skin itself. It was found that if the treated Australian skins were allowed to stand for two weeks or more that the penetration under these areas was good. As the surface of the skin is not directly exposed in these areas this slow penetration is not believed to be a problem.

Example 7.

Based on the trials to date it is felt the dry preservation mixture below will offer the greatest sodium chloride reduction, though later trials may identify additional mixtures.

10% potassium chloride

4% to 5% oxalic acid

1 % to 5% benzoic acid

5% to 8% sodium chloride (possibly replaced with zeolites or other dispersants) 0.1 % to 0.2% fungicides (though lower strength fungicides may require higher levels)

Example 8.

Skins preserved with 5% oxalic acid as the solid acid have been successfully pre- tanned using a conventional chrome free process. This involved soaking in brine, fleshing and pre-tanning with chrome free chemicals. The resultant product produced commercially acceptable finished leather. Example 9.

Results from earlier oxalic acid trials using between 3% and 5% oxalic acid to determine how quickly the oxalic acid is consumed are shown in table (v):

Table (v).

W + P = mass in grams present in the wool + pelt;

W = mass in grams in wool; P = mass in grams in pelt;

End = % of added oxalic acid remaining at the end of the trial.

Example 10.

Results from LASRA (New Zealand Leather and Shoe Research Association Incorporated) accelerated mould test procedure for a variety of mixes is shown in table (vi). This test involves inoculating samples of the treated skins with 15 known moulds then incubating at 25°C and 100% relative humidity. Samples are inspected every 7 days and fail if any mould colonies have established on the samples. Table (vi)

PAS = pH after 24day/63 day storage DTFMT = days to fail mould test

+ after a number = number of days in test without showing any mould and test is still ongoing.