FR2771258A1 - Treatment and storage of shelled walnuts - Google Patents

Abstract

Walnuts are frozen at -40 <0>C after harvest, and stored at -20 <0>C, still in their shells, for up to four months, then thawed for shelling. This is done manually, after 2-4 hours at room temperature. The kernels are packed in a container which excludes light, in a non-oxidising atmosphere and frozen. An Independent claim is made for the final product.

Description

TECHNICAL AREA
The present invention relates to the agro-food industries and more especially to processes for the preparation and preservation of walnut kernels.

The invention will be described in relation to its application to walnuts of the walnut type, but it is applicable to various types of walnuts.

PRIOR TECHNIQUE
We know that the walnut, traditionally used for the production of oil, is currently sought after both for its organoleptic qualities and for its dietary properties, linked to the presence of unsaturated fatty substances providing a lipid balance within the body and promoting the stabilization of hypercholesterolemia levels. For these various reasons the use of nuts, and more exactly walnut kernels, is developing considerably in the production of food products relating to confectionery, pastry making or even cheese making or catering.

However, the development of this form of exploitation comes up against specific difficulties, linked in particular to the presence of unsaturated lipids in the walnut kernel, making this fruit sensitive to sources of oxidation and therefore susceptible to rancidity. This problem did not exist in the context of the production of walnut oil, which could be carried out during the period immediately following the harvest period, the final product in liquid form being able to be packaged in flasks or bottles and thus released. away from atmospheric oxygen.

In the case of the largely new pastry, cheese or catering operations mentioned above, the product used is the walnut kernel, the preparation, packaging and storage of which encounter problems which limit their exploitation. Oxidation, both superficial and at the heart of the product, should in fact be avoided, which alters both the beautiful ivory-white appearance and the taste and quickly renders it unfit for consumption.

So that the exploitation of walnut kernels in food, artisanal or catering preparations, and all the more so in semi-industrial preparations, has not been able to find the place that the taste and the dietary interest of this would justify. type of product.

In fact, no marketed form of the walnut kernel is currently known except in the dry or desiccated form, a form which has largely lost the taste quality of the fresh product, like its appearance, affected by the phenomenon of yellowing. In addition, the kernel in dry form remains difficult to peel, an operation which in any case requires a high consumption of labor time; chemical removal of the skin is unsatisfactory because of the traces of residual negative flavor left on the final product.

The distribution of peeled kernels at the production level, therefore skinless, and kept in the cold, could not originate and even less develop because it comes up against many difficulties; the main one being that the kernel can only peel itself from a fresh walnut for a relatively short period of time (after harvest) not exceeding one month. The output of an operator, given the slowness of the operation, does not however exceed one kg / day of peeled kernel; so that it is not possible, within the time limit of one month, to have the manpower and the corresponding logistic support, to process marketable quantities able to meet the potential demand.

But even more the operation of peeling remains delicate taking into account the configuration (division into lobes and cerebriform surface) of the fruit; and experience shows that we only collect (approximately) a rate limited to 1 "o of intact kernels, for 39 of marketable pieces and 60% of invalids, which leads to a significant waste in terms of valuation of the product, the intact kernels being of a very higher price.

DISCLOSURE OF THE INVENTION
The invention overcomes these drawbacks and allows in a new way the exploitation of fresh walnuts for the production of skinless kernels, their conservation over time and their distribution while preserving the qualities of the fresh product. Another object of the invention is to considerably facilitate the operation of removing the skin and consequently to significantly increase the hourly output of the operators and the profitability of the operation. A new object of the invention is to enable the production of skinless kernels in a considerably improved presentation; this both in terms of the white color saved over time after storage, and in terms of obtaining a proportion of whole kernels, thus ensuring a consequent valuation of the product.

The invention relates to a process for the preparation and preservation of walnut kernels, characterized by the succession of the following operations: a) the fresh walnuts in their shell are subjected to freezing, as soon as they are harvested, b) the walnuts after a period of cold storage are thawed; c) the walnuts thawed in this way are opened and the kernels separated from the shells are peeled manually, the previous freezing / thawing phases having caused the skin to separate and allowing rapid detachment of the skin while keeping a high percentage of kernels intact; d) the peeled kernels are packaged and subjected to final freezing to be stored and distributed in a cold chain.

The initial freezing of the nuts in their shell is carried out at a temperature of the order of -20, this for a maximum period of five months and preferably less than four months.

Preferably, phase b) of thawing the nuts in their shell is carried out by exposing the nuts to room temperature for a period of 2 to 4 hours at most.

Advantageously, during phase c) the peeled kernels, as the skins are removed, are protected from light while awaiting packaging.

According to yet another more particular characteristic of the invention, the kernels are packaged in opaque envelopes, protecting them from light.

And according to an alternative embodiment, the packaging of the kernels is carried out by keeping the kernels conditioned in a non-oxidizing gaseous atmosphere, for example by injection of nitrogen or carbon dioxide or alternatively under vacuum.

More particularly, phase d) of final freezing is carried out by passing the conditioned kernels through a nitrogen freezing tunnel, at a temperature between -120 and -130.

And preferably the storage of the kernels which have thus been subjected to deep freezing is carried out in a cold room, the kernels being maintained at a temperature of the order of −200.

EXPOSURE OF AN EXAMPLE OF AN IMPLEMENTATION
Other characteristics of the invention will emerge from the description which follows and which is given in connection with an exemplary embodiment presented by way of illustration and not by way of limitation.

A stock of 210 tonnes of fresh walnuts was made right after harvest; the nuts as the successive collections at a rate of 10 tons per day were placed in trays or perforated plastic tubs.

The successive batches of fresh walnuts are subjected to a first freezing, by passage through a rapid freezing tunnel at a temperature of -40 ° C., which causes freezing to the core in a few four hours.

The products in the frozen state are stored in cold rooms at a temperature of the order of -20 C, for a period of four months or more, a period during which the product does not evolve, being removed by the cold from the sources. degradation and thus keeps intact all the properties of the fresh.

This retention period is then used to process the products; the batches are taken from the stock successively to undergo shelling, by breaking the hulls and separating the kernels. Prior to this treatment, the nuts are thawed at room temperature for a period of two to four hours at most; the thawed walnut, at least superficially at the level of the kernel, has all the qualities of a fresh walnut.

The kernels separated from the shells, which are evacuated, are then returned to the workshops where the operators will proceed to the manual removal of the skins.

It was found that following the treatment described above, the skins are removed very easily and much more quickly than when peeling a fresh walnut; a saving of time, and therefore of productivity of 30%, compared with the peeling of fresh walnuts which have not undergone the freezing phases described, has been observed.

We can consider that this unexpected advantage is linked to the physical phenomena affecting the product during the previous cycle; the differential expansion coefficients between the skin of the kernel on the one hand and the flesh of the kernel on the other hand, linked to the significant thermal gradients experienced by the product during the freezing / thawing phases, cause superficial detachment and separation of the skin relative to the flesh of the almond; so the removal of the skin is obtained very easily, since the latter adheres only slightly to the surface of the fruit.

Furthermore, the tests described here have led to the observation of another important and essential advantage of the method according to the invention; after peeling, a percentage of intact whole kernels is obtained, considerably higher than that achieved during conventional operations for removing the skins from kernels originating from fresh walnuts picked or collected.

In fact, whole kernels intact after peeling represent from 30 to 50% of the products obtained instead of the percentage of 1% obtained in the peel of kernels not previously frozen and then thawed; waste or invalids of low commercial value represent 40% of the products obtained, while the pieces (lobes or half-lobes) represent 10% of the total obtained.

This surprising and also unexpected result, linked to the implementation of the method of the invention, is undoubtedly to be correlated with the preceding one; insofar as the removal of the skins is facilitated, the handling of the kernels is carried out under gentler conditions, and the tensile forces or stresses which it undergoes during these operations are then lighter and are less likely to cause a rupture or dismemberment of the whole kernel.

In addition, and thanks to the implementation of the method of the invention, it occurs that the kernels peeled at the end of an immediately preceding thawing phase have a superficial skin, warmed first by the ambient atmosphere and therefore having regained its originality. natural flexibility, while the heart of the fruit, less affected by heating, is still at a low temperature, possibly still at a temperature close to 0 C, either still negative or slightly positive; at this low temperature, the heart of the fruit is still stiffened and homogenized by the cold, which allows it to consolidate its natural structure and to better resist the external mechanical stresses which would tend to break its unity.

It can thus be seen that if the invention uses a known process for a first result also known, namely the preservation of food products by cold, it makes it possible here to obtain, in addition and above all, two new, specific and unexpected results: an ease in the peeling operation with an increase in yield of 30% and, what is better, a high valuation of the finished product with a high percentage of intact products obtained after removal of the skin.

The economic interest of the invention is therefore considerable by allowing a very significant gain in added value in the production of skinless kernels from a given harvest of walnuts, the commercial value of intact kernels being considerably greater than that. pieces.

The kernels thus obtained are, as they are peeled, protected from light in an opaque container, in order to avoid too rapid surface oxidation altering their desired white color.

These products are then subjected to deep freezing by passing through a deep freezing tunnel at a temperature between -120 C and -130 C; this hardening by deep cold allows to freeze the taste and organoleptic properties of the kernels.

It accentuates and enhances the whiteness of the product which lasts over time for up to twelve months or more.

The kernels thus treated are packaged in batches or commercial units, for example in opaque pouches and in boxes sealed with adhesive strips, then stored in a cold room at a temperature of -20 C.

User-defrosted products can be used maintaining their perfect whiteness for a period of 24 to 48 hours, while still providing the fresh taste, flavor and crunch of fresh walnuts.

In summary: it is recalled that to date there is no marketing of kernels without their skin; the known treatment methods make use of mechanical washing or chemical processes affecting dried kernels, with or without skin, but therefore always resulting in dried kernels.

The invention now makes it possible in a new way to produce and keep for twelve months and more kernels already stripped of their skin and exhibiting the taste of the fresh and the white color of the kernel obtained from the fresh walnut.

As previously explained, the raw harvested walnuts are frozen immediately, then thawed as they go in order to shell the walnuts and remove the skins of the kernels, an operation facilitated and accelerated as a secondary result of the previous phases of freezing / thawing; and moreover the operation under these conditions makes it possible to obtain 30 to 50% of intact kernels; the peeled kernels are then subjected to final deep freezing with liquid nitrogen to approximately -120 ", thus increasing not only the productivity of the treatment but the taste properties and the whiteness of the kernel.

The invention thus provides agrifood industries, such as craft activities and finally catering, a completely new product in itself, permanently available throughout the year.

And to this end the invention relates, in addition to the method described, and as a new industrial product in itself, kernels stripped of their skin, preserved by cold and having the taste properties and whiteness of the fresh product.

The temperatures indicated in this specification are expressed in degrees centigrade. The technical data set out above are presented by way of illustration and it is possible, without departing from the scope of the invention, to make modifications or arrangements.

Claims (8)

CLAIMS 1- Process for the preparation and conservation of walnuts, characterized by the succession of the following operations: a) the fresh walnuts are subjected to freezing, as soon as they are harvested, in their shell, b) the walnuts after a period of conservation by cold are thawed; c) the walnuts thawed in this way are opened and the kernels separated from the shells are peeled manually, the previous freezing / thawing phases having led to a detachment of the skin and allowing rapid detachment of the skin while preserving intact a high percentage of kernels; d) the peeled kernels are packaged and subjected to final freezing to be stored and distributed in a cold chain. 2- A method according to claim 1 and characterized in that the initial freezing of the nuts in their shell is carried out by passing through a tunnel at a temperature of the order of -40 C, the nuts then being stored at a temperature of the order of from -20 C, this for a maximum period of five months and preferably less than four months, 3- Method according to claim 1, characterized in that the phase b) of thawing the nuts in their shell is carried out by exposing the nuts at room temperature for a period of 2 to 4 hours maximum. 4- Method according to claim 1, characterized in that during phase c) the peeled kernels, as the skins are removed, are protected from light pending their packaging. 5- Method according to claim 1, characterized in that the kernels are packaged in opaque envelopes, shielding them from light, and the conditioning of the kernels is carried out by maintaining the kernels conditioned in a non-oxidizing gaseous atmosphere, by for example by injection of nitrogen or carbon dioxide. 6- A method according to claim 1, characterized in that the phase d) of final freezing is carried out by passing the kernels conditioned in a tunnel freezing with nitrogen, at a temperature between -120 C and -130 "C. 7. Method according to claim 1, characterized in that the storage of the kernels which have thus been subjected to deep freezing is carried out in a cold room, the kernels being maintained at a temperature of the order of - 200C. 8- A method according to claim 1 and claim 3, characterized in that the thawing is stopped and the kernels subjected to manual skin removal operation, when the surface of the kernel, that is to say its skin, has exceeded a positive temperature, the core of the kernel still being at a temperature close to a negative temperature. 9- As a new industrial product, kernels stripped of their skin, preserved by cold and exhibiting the taste properties and the whiteness of fresh kernels. 10- Walnut kernels according to claim 9 and obtained by the implementation of the method according to one of claims 1 to 8 above, the nuts having been frozen as soon as they are harvested, then thawed for peeling and peeling of the kernels, this operation manual being facilitated by the separation of the skins following the previous freezing / thawing phases and allowing a percentage of 30 to 50% of intact kernels to be obtained, the peeled kernels then being subjected to deep freezing at a temperature of the order of from -120 "C then stored in a cold room at about 20" C.