GB2038610A - Dehydrated vegetables - Google Patents

Abstract

Dehydrated vegetables, e.g. legumes, are produced by impregnation with an aqueous solution containing at least one substance capable of complexing polyvalent metal ions, e.g. a citrate, and then drying, wherein prior to drying the vegetables are: (a) optionally soaked in a liquid, aqueous medium (b) precooked in a liquid and/or vaporous, water-containing medium and (c) cooled to a temperature of about 50 DEG C maximum, with the proviso that at least one of the process steps (a) to (c) is performed in the presence of the aqueous impregnating solution.

Description

SPECIFICATION Process for producing dehydrated vegetables in pieces with reduced preparation times, dehydrated instant vegetables in pieces, and use of same This invention relates to a process for producing dehydrated vegetables in pieces with preparation times reduced by the incorporation of at least one substance capable of complexing polyvalent metal ions (complexing agent), especially a citrate, which can be prepared for consumption by introducing them into a hot, especially boiling, aqueous rehydrating medium and briefly allowing them to stand for no more than about 5 minutes (instant dehydrated vegetables), from fresh or field-dry vegetables or pieces of vegetables by impregnation with an aqueous solution containing at least one complexing agent and by drying, instant dehydrated vegetables, especially instant legumes, and the use of said products as or in dehydrated soup and/or dehydrated casserole mixes.

The term "instant" as defined in this invention refers to a product which, as has already been mentioned, can be prepared for consumption, i.e. can be rehydrated and cooked, by moistening it with hot, especially boiling water and briefly allowing it to stand for no more than about 5 minutes.

As legumes are known, on the one hand, as the types of vegetables which are most frequently offered in the form of dehydrated vegetables and preparation of dehydrated legumes, on the other hand, is particularly time-consuming and since attempts to create dehydrated vegetables (in pieces) with reduced preparation times or even with instant properties have had comparatively little success, especially as far as legumes are concerned, the below appraisal and description of the relevant state of the art as well as of the invention are given chiefly by reference to these types of dehydrated vegetables which are particularly difficu It to handle.

Apart from canned and frozen products, dehydrated vegetables constitute, no doubt, the most common storage-stable form in which vegetables in pieces are marketed. As far as legumes are concerned, leaving aside canned products, they are still offered today chiefly in the form of the field-dry seeds, preferably of peas, lentils and beans. To prepare these seeds for consumption it is generally necessary first to soak the seeds and then cook them for 30 minutes to several hours. It is only logical, therefore, that quite a number of "kitchen tricks" have been described for the ordinary preparation of these vegetables by the housewife in order to simplify this inconvenient procedure and especially to reduce preparation times.In exactly the same direction go the efforts made by breeders tocultivatevarieties with properties particularly suitable for the consumer or the industry, e.g. with shorter cooking times. This applies, though to a different extent, to other types of vegetables as well.

Now dehydrated vegetables, casseroles etc. are a form of food which is meant to make preparation of such dishes easier for the housewife or for institutional users and which is meant to reduce preparation as a whole to cooking and preferably short cooking or, at any rate, to cooking for an exactly defined period. Eecause oftheirvery bad and also highly varying cooking behaviour legumes in the form of their air-dried seeds normally are unsuitable for the production of such dehydrated products. In order to obtain legumes which are more suitable for the production of such products, the seeds are usually soaked, precooked and subsequently dried. As a result of such a pretreatment, called also "preparation process", products are obtained whose cooking times vary from 15 to 30 minutes, depending on the raw materials and process or drying conditions involved.These products today are the common raw materials for dehydrated soups, casseroles etc.

When comparing these cooking or preparation times with those of other convenience products, especially other dehydrated soups, bouillons etc., they must still be called extraordinarily long.

Numerous attempts have therefore been made to further reduce the preparation or cooking times of dehydrated vegetables in general and of legumes in particular.

Most of the processes so far developed for reducing cooking times are based on the long-known phenomenon that divalent cations, especially of calcium, which occur in protopectin itself but, originating from the cell sap or the cooking water, may also be bound to the pectin, impede the steeping process and the degradation of the pectin during cooking.

Therefore, in all these known processes reagents capable of calcium exchange or reagents complexing calcium are used in orderto improve the cooking behaviour.

A very comprehensive analysis of these facts in relation to the cooking behaviour of field-dry peas is given by S. MATTSON in his studies of the dependence of the cooking behaviour of yellow peas on pH, water hardness, NaCI, KCI and/or CaCI additives, phytic acid content, and phytase activity. As a result of these studies he ultimately proposed a mixture of trisodium and disodium phosphate as an optimum means for reducing cooking times. This phosphate mixture is added to the soaking water. The proposed treatment method therefore merely represents a process for reducing the cooking time of unusually slow-cooking peas to the average cooking time of normal peas in a usual preparation process, which exclusively comprises soaking and cooking to a ready-to-eat state, as it is commonly applied by the housewife.MATTSON does not mention a treatment aimed at something else than preparation for immediate consumption, e.g. the production of quick-cooking dry peas.

Such a treatment, which is also based on the use of mixtures of different alkali phosphates, is known however from US patent 3,108,884 in which beans are treated at temperatures up to 50"C with phos phate solutions. The bean subjected to this treat ment (which may include a blanching step) and finally dried show a much shorter cooking time of about 45 minutes, compared to about 3 hours needed for untreated beans.

Various phosphates as well as other complexing agents in combination with various salts (although, in practice, apparently only sodium hydrochloride is used) are proposed e.g. by ROCKLAND in quite a number of patents, in which impregnation with these additives in a so-called "vacuum hydration process" is a compulsory feature (US patents 3,318,708,3,352,687,3,635,728 and 3,869,556). Here again the beans are simply dried after the proposed treatment and are cooked only when prepared for consumption. The cooking times achieved with these processes still amount to between about 25 and 30 minutes and specifically apply to the preparation of baked beans which are very popular in the United States. Beans of this type must have a much greater firmness in the ready-to-eat state than the beans used in the casserole dishes customary in Central Europe.To achieve a degree of tenderness sufficient for casseroles, the cooking time of the beans would have to be increased to about 50 to 60 minutes, as a duplication of the processes disclosed in the ROCKLAND patents has shown. No mention is made in the ROCKLAND patents of the amounts of salt left in and to be consumed with the product.

Complexing agents with a particularly marked effect of reducing cooking times, according to the state of the art, are EDTA and especially citric acid and/or alkali citrates, which in connection which vegetables which are not particularly problematic in this respect, e.g. carrots, in some cases in fact permit a considerable reduction in cooking times.

The chances as well as the limits of this state of the art may be seen from German OS applications 1 802 941 and 2 122 531 which recommend a treatment with citric acid or its alkali salts as calciumcomplexing and pectin-degrading agents for reducing the cooking times of vegetables.

But these known processes are also unable in several respects to solve the problem in question in a fully satisfactory way.

According to German AS application 1 802941 the complexing agents incorporated in the vegetables immediately before they are dried, e.g. by immersion in or spraying with a complexing-agent solution, or they are added to the dried vegetables orto a soup mix containing the dried vegetables, optionally during cooking. A special treatment, e.g. blanching or precooking, is not envisaged and is even said to be unsuitable. The cooking times indicated for the vegetables mentioned (as far as legumes are concerned, only peas are mentioned) range at about 5 minutes. The chief disadvantage of this process is that an amount of alkali citrate corresponding to at least 5% w/w citric acid dihydrate (referred to vegetable solids) is needed to achieve this reduction in cooking time and remains in and is consumed with the product.

In German OS application 2 122 531 alkali salts of citric acid as well as other complexing reagents are recommended for treating vegetables. Treatment with the complexing agent may be performed in the most different ways either prior to or after drying, but precooking is expressly to be omitted. The cooking time achieved in this way for peas is 18 minutes compared to 24 minutes needed for peas which have just been punctured and blanched prior to drying.

The amount of citrate incorporated in the vegetables by such treatment is not indicated but the examples show that it generally ranges between 10 and 20% w/w, referred to vegetable solids. Nevertheless, dehydrated vegetables with instant properties as defined in this invention are at best obtained in this known process if extremely large amounts of complexing agents are added, which are undesirable on account of their disturbing flavor properties alone, and also if vegetables are used which by nature have a short cooking time and which have been cut into relatively thin shreds.

Another way of obtaining quick-cooking dehydrated vegetables is known from German patent 2 260 which recommends a treatment with pectolytic enzymes in combination with the soaking process for lowering the cooking time of peas and in which the peas are cooked with steam and are subsequently dried. Such a treatment lowers the cooking time from between 18 and 25 to between 8 and 12 minutes.

Entirely different roads are followed by some other known processes in which degradation of the protein by means of proteases or impregnation with water-soluble additives is tought.

B.S. BHATIER and co-workers, for instance, suggest a treatment of beans with papain during the soaking phase or after the precooking and priorto the drying step. Such a treatment reduces the cooking time from between 10 and 60 minutes for untreated beans to between 3 and 17 minutes simply by precooking and to between 1 and 7 minutes by precooking and an additional treatment with enzymes.

This means that apart from the decisive reduction in cooking time brought about by the precooking step a further reduction is achieved by the treatment with enzymes. However, very short cooking times are obtained merely for vegetables which by nature are already quick-cooking. Apart from the fact that this known process, while permitting a substantial reduction in cooking times, does not yield products with instant properties, it is unsatisfactory chiefly because of the effect of the enzyme, which largely depends on the raw material involved, because of the high cost in terms of money and time generally connected with the use of enzymes as well as because of the more or less unavoidable development of a strongly bitter taste which is probably due to the formation of so-called bitter peptides.

In German AS 1 492707 an improvement in the appearance of legumes with a simultaneous reduction of the cooking time to between 15 and 25 minutes is achieved by impregnation with edible mono-, disaccharides or polyhydric alcohols either alone or in combination with common salt, soda and sodium sulfite at 900C and subsequent drying. The amounts of additives remaining in the products again are extremely high and, for achieving the effect described, must accountfor at least 30%.

Impregnation with a soluble salt is casually recommended also for deep-frozen, then thawed and precooked green peas in US patent 3,493,400 which, in essence, describes the production of precooked toasted onions.

There is no exact comparison made of cooking times but mentioned merely that salt-treated peas are softer after 2 minutes of cooking than peas not treated with salt. A disadvantage of this process certainly again is the very high salt content of the product, with common salt accounting for the largest portion (45%).

Freezing of precooked starchy vegetables is proposed by CH. FELDBERG and co-workers as well as by US patent 2,813,796. The term "starchy vegetables" is used by the former authors exclusively for beans while in the US patent it refers preferably to rice. A feature common to both proposals is the claim that the development of ice crystals in the freezing phase partially destroys the cellular tissue and thus favors both the escape of water during drying and the entry of water during rehydrating The development of large ice crystals capable of destroying the tissue and the starch gel, therefore, is expressly claimed in US patent 2,813,796 and slow freezing proposed. The cooking times achieved in this manner in the US patent by soaking, cooking, cooling, freezing, thawing and drying of rice range at about 5 minutes.A critical point in this process is cooking inasmuch as overcooking of the rice grain, i.e. excessive swelling of the starch, has to be avoided.

No improvement in cooking behavior but merely an improvement in the drying rate (improved escape of water following ice-crystal development) as well as an improvement in the appearance (no bursting during drying on account of the escape of water facilitated by the ice-crystal formation) are envisaged by CH. FELDBERG and co-workers. The influence which freezing may have on the cooking behavior was not investigated at all, but merely the appearance of differently treated beans compared after a constant cooking time of 5 minutes. Therefore, it is not obvious from this publication whether and to what extent such a freezing step is capable of lowering cooking times.The softness ratings given in table 2 of this publication for frozen and nonfrozen but otherwise identically treated samples, on the contrary, even convey the impression that the non-frozen samples, although being generally rejected on account of their poorer retention of shape, definitely cook to a softer state than the frozen ones.

The finding that a reduction in cooking times by freezing and ice-crystal growth is possible with high-starch vegetables either to a limited extent only or not at all, strictly speaking, is not surprising because starches present in solution or as a gel (cooked legumes contain gelatinized starch as their main component) are known show a strong tendency to retrograde upon freezing. During retrogradation the starch recrystallizes and loses its waterbinding power. The retrogradation process can be reversed only at very high temperatures (approx.

130"C), that is to say at temperatures which do not normally occur in ordinary cooking. So retrograded starch cannot be re-converted under normal cooking conditions into the optimum swollen state as it is present after gelatinization. The fact that starch which has retrograded upon freezing cannot easily be returned into an optimum swelling state, incidentally, seems to be the reason why in the pretreatment of rice according to US patent 2,813,796 the cooking process is particularly critical.Only in an incompletely swollen starch gel is it possible on the one hand to loosen the structure by ice-crystal formation and, on the other hand, to restrict retrogradation, which is much lower in ungelatinized or incompletely gelatinized starch, to a point where the water penetrating into the porous structure meets with a sufficiently large amount of nonretrograded starch, i.e. starch to be gelatinized under cooking conditions, to ensure that a good texture, i.e. sufficiently swollen starch, is present in the rice grain after a cooking process which has even been additionally shortened. The total reduction in cooking times achieved with this known process, therefore, is the result of two effects which, strictly speaking, are contradictory, i.e. an acceleration of the access of water and the preservation of starch capable of gel formation.

Summarizing the state of the art is noted that, although a number of different processes are known according to which dehydrated vegetables of all kinds with more or less greatly reduced cooking or preparation times may be obtained, the production of instant dehydrated vegetables in pieces according to the known processes usually is not possible at all or, if it is possible, requires the use of vegetables which by nature are relatively quick-cooking and presupposes unacceptably great efforts and/orthe incorporation of very large amounts of additives which heavily impair the quality of the product.

It has therefore been an object of this invention to create a process which avoids the disadvantages of the state of the art and in particular permits the production of dehydrated vegetables from practically any type of vegetable in a comparatively simple way using relatively small amounts of additives, said dehydrated vegetables having instant properties even when present in comparatively large pieces, and to make available dehydrated vegetables in pieces which in spite of a low content of complexing agents show instant properties.

This object of the invention is accomplished in the manner disclosed in the main claim on the basis of the surprising finding that, by the per se known addition of complexing agents in amounts which according to the state of the art do not have any sizeable effect on cooking or preparation times or at best bring about a more or less substantial reduction of these times, instant dehydrated vegetables are obtained from practically any type of vegetable if the complexing agent is incorporated in the vegetables, which have been pretreated in the traditional manner, prior to drying by treatment with an aqueous impregnating solution containing at least one complexing agent and if the vegetables are precooked prior to drying in a liquid and/or vaporous aqueous medium and are then cooled, preferably rapidly, from the precooking temperature to a point where the vegetable temperature is no more than about 50"C, preferably no more than about 40"C and most preferably less than about35"C.

A subject of the invention furthermore are instant dehydrated vegetables in pieces according to the foregoing claims 15 to 17 as well as the use, covered by claim 18, of instant dehydrated vegetables of the invention and/or produced according to the process of the invention.

The obviously essential advantage of the invention is that, in a reliable and simple way, it leads to dehydrated vegetables in pieces which show instant properties although they contain complexing agents in only a fairly small amount which neither affects the taste nor is disturbing in any other way and which even for legumes, i.e. the type of vegetable usually requiring notoriously long cooking or preparation times, is far below the levels which according to the state of the art are required even for compartively quick-cooking vegetables to achieve but a significant reduction in cooking times (at least 5% w/w, referred to vegetable solids), and which usually is even below 2.5% w/w.

The optional soaking treatment of the invention, although not absolutely necessary in each individual case, is frequently advisable and recommended especially when relatively slow-cooking vegetables, especially high-starch vegetables and notably fielddry legume seeds or cereal grains, are used as starting materials.This treatment, as a rule, fulfills several functions among which the following ones play the largest role: In connection with field-dry, high-starch seeds, especially legumes, the soaking treatment ensures that the water content required for gelatinizing the starch is present in the seeds during the subsequent precooking step, and it is therefore absolutely necessary if the vegetables are precooked in a vaporous aqueous medium or is at least advantageous if the vegetables are precooked -- which is less advisable for several other reasons -- in a liquid aqueous medium.

The soaking treatment may reduce the duration of the subsequent precooking step, which is desirable especially for vegetables which are comparatively slow-cooking and/or which have to be cooked to a ready-to-eat state during precooking, that is to say chiefly for high-starch seeds, both in terms of process technique and in view of the detrimental effect which prolonged heating to high temperatures inevitably has on the product quality.

Since impregnation with the complexing-agent solution can be accomplished simultaneously, none of the subsequent process steps must be performed in the presence of a liquid aqueous medium, which may be desired and advantageous during precooking in most instances and may be desired and advantageous during cooling in some of the cases, namely ifthe precooked vegetables during cooling are frozen, since in that case the temperature of the precooked vegetables may quickly be lowered by simple evaporation to values at which further cook ing is excluded and the vegetables at the moment when they are frozen are free from adhering water thus permitting more efficient freezing and drying.

A preferred embodiment of the process of the invention for the production of high-starch instant dehydrated vegetables, especially legumes, there fore comprises the following steps: (a) Soaking the field-dry seeds in an aqueous trialk ali citrate solution, (b) steam-cooking the soaked seeds, (c) freezing the cooked seeds and maintaining them in a frozen state, (d) drying the frozen seeds (preferably without previous thawing) with the particular drying method not constituting a critical feature with regard to the instant character of the products.

The most favorable drying method, economically, is with hot air.

The soaking time depends on the seed variety used. It largely corresponds to the time which is needed for a maximum adsorption of water during swelling. Common and representative times are about 4 to 5 hours for lentils, about 6 hours for white beans and about 12 hours for peas, although longer soaking periods of 16 to 18 hours are not critical for all three varieties.

The temperature of the soaking water should preferably correspond approximately to room temperature (about 20"C). Critical and not preferred are temperatures over about 35 to 40"C and especially over 50"C while lower limits are set by the freezing point of water.

The weight ratio of soaking water to vegetable notably for legumes preferably is about 2.5:1 and should be adhered to as exactly as possible.

The concentration of complexing agents depends on the type of vegetables involved and is lower for seeds and vegetables which by nature have a good cooking behaviour than for very slow-cooking ones.

An increase beyond the levels just required for the various varieties usually offers no further advantages. As a general rule, impregnating solutions with a concentration of complexing agents up to 4.8% are more than sufficient; mostly a concentration not over 4.0 and frequently of less than 3.0% w/w is sufficient. In many cases even impregnating solutions with complexing-agent contents of only 2.5% and less were found to be perfectly sufficient.

Consequently, as already mentioned, the amounts of complexing agents incorporated in the vegetables in the process of the invention are surprisingly low.

Even for legumes, which are known to require particularly long cooking times, they range from about 0.5 to 2.5 and especially from about 0.7 to 1.3, a level which is even distinctly lowerthan the levels that are required, according to the state of the art, for quickcooking vegetables to achieve but a significant reduction in preparation times.

To illustrate this surprising circumstance it is mentioned that, for instance in the production of instant legumes according to the process of the invention using alkali citrates as complexing agents, the amount of citrate remaining in the product is of the order of 1% (referred to solids) and thus not essen tiallyabovethenatural citrate content of the legumes and, compared to other types of veget ables, e.g. potatoes etc., is considerably below the naturally occurring citrate contents.

In a preferred embodiment of the invention the complexing agent(s) is (are) incorporated in the veg etables by soaking and/or cooling in an impregnat ing solution containing said complexing agent(s).

Which of the various alternatives described should be preferred in each individual case depends chiefly on the type of vegetable used. As a general rule one may say that vegetables which by nature are slowcooking, which are to be precooked to a ready-to-eat state, which have a hard-to-cook skin, a high starch content and/or, in the condition in which they are delivered, a low water content, e.g. legumes, are recommended to be soaked in impregnating solution prior to precooking while in connection with vegetables which by nature are relatively quickcooking, which need not be cooked to a ready-to-eat state during precooking but are merely to be parboiled or blanched, which have a low starch content and/or a high natural water content, it is advisable to incorporate the complexing agent(s) by cooling in an impregnating solution, and that in those cases where the precooked vegetables are cooled to a for zen state it is generally inappropriate to treat the vegetables with an aqueous impregnating solution during cooling.

Precooking in the process of the invention preferably takes place at elevated pressure and, consequently, at temperatures above 100"C in order to keep the precooking time as short as possible.

Although the vegetables in the process of the invention may, in principle, be precooked also in a liquid aqueous medium and this method may even be advisable in some cases, for instance when vegetables are involved whose marginal areas cook slower than the center, precooking in a mixed-phase or in a purely vaporous medium is generally preferred, especially for vegetables which are relatively quick-cooking and/or which show a high water content and where exact precooking times are to be adhered to and/or where cooking in a liquid aqueous medium entails the danger of "overcooking" of the marginal areas.

Steam-cooking times and temperatures (pressures) also depend chiefly on the vegetable variety involved. Typical times and pressures are 35 minutes and 1.2 to 1.5 bar for lentils, 55 minutes and 1.2 to 1.8 bar for white beans, while 85 minutes and 1.1 to 2 bar are needed for peas.

As regards the extent to which vegetables should be precooked, it is recommended that high-starch vegetables, especially legumes, are subjected to more intensive precooking, preferably to a readyto-eat state, while for the other types of vegetables it is usually sufficient and preferred to precook them partially or simply to blanch them during precooking.

As already mentioned, precooking in the process of the invention is foilowed by a cooling step which should be accomplished as quickly as possible to a temperature of about 50"C maximum, preferably 40"C maximum and most preferably about maximum in order to avoid that the cooking process continues in an uncontrolled manner.

With regard to the above temperatures it should be noted that although a number of vegetables, especially those with a low starch content, need not be cooled below the temperature limits specified in orderto achieve the desired instant properties, other vegetables should preferably be cooled to even lower temperatures. For vegetables with a high starch content, for instance legumes, it is usually even necessary or at least advisable to cool them until they are frozen.

In those cases where no freezing is needed, the cooling step is performed preferably in a liquid aqueous medium, most preferably in an impregnating solution containing the complexing agent(s).

This embodiment of the invention, surprisingly, has as a rule been found to be advantageous in the prep aration of vegetables which by nature are quickcooking and which, as mentioned previously, during precooking are not cooked to a ready-to-eat state but preferably are merely blanched.

In the embodiment of the invention in which the precooked vegetables are frozen during cooling, the goods are cooled preferably to temperatures of about -10 to -350C. Following the freezing step the vegetables may, in principle, be dried immediately but experience has shown that it is frequently advantageous to keep the goods in frozen condition for a prolonged time prior to drying, preferably for 2 to 36 hours, more preferably for about 12 to 24 hours, and most preferably for about 14 to 18 hours.

Unexpectedly, present experience indicates the freezing rate not to be particularly critical, which means that the effect envisaged by the invention is achieved even when relatively fast freezing rates are employed so that no large ice crystals may form which would at best explain the favorable effect of the freezing step on the rehydrating behavior or the product.

It is also surprising that it is not only possible but usually even necessary to use this embodiment of the invention also and in particular for vegetables which have a high starch content and have been precooked to a ready-to-eat state, especially legumes, in order to achieve the desired instant properties since the state of the art suggested that freezing, notably rapid freezing, had exactly the opposite effect on vegetables with a high content of gelatinized starch, for instance on legumes precooked to a ready-to-eat state.

Steam-cooked products may be frozen either immediately or preferably after a brief evaporation and cooling time of about 5 minutes according to any desired method, e.g. in the freezer.

Frozen vegetables need not be thawed priorto final drying and in the process of the invention, for convenience, are as a rule directly subjected to the drying step.

Suitable drying systems are hurdle or belt dryers which are commonly employed for vegetables and especially legumes and which must ultimately lead to a final water content of the products below 10%.

The preferred final water content is between 5 and 7%. Optionally the frozen vegetables may also be freeze-dried but this method does not offer any advantage over much cheaper air drying as far as the instant properties of the products are concerned.

The complexing agents used in the process of the invention are preferably citrates and especially alkali citrates.

The dehydrated vegetables produced according to the process of the invention need not be cooked to prepare them for the table even if they have not been cooked to a ready-to-eat state during precooking but have, for instance, merely been blanched. As Examples 1 to 3 show, it is sufficient even for legumes to moisten them with hot water. In this context it is regarded as essential that this optimum reconstitution takes place also in the presence of a so-called "real" soup mix which apart from fat and protein is known to contain binders, e.g. starch.

In addition to the improved cooking behavior the process of the invention offers the advantage that, when using potassium citrate, which occurs naturally in almost all fruits and vegetables, as a complexing agent, a leaching-out of this substance is prevented and shifts in the mineral composition, as they occur with sodium salts, phosphates and other complexing agents, are avoided.

The following examples and comparative tests illustrate the invention and evidence the surprising effect achieved by the combination of measures of this invention.

Example 1 100 kg lentils are soaked at room temperature (approx. 20"C) in 250 liters of tap water in which 5 kg tripotassium citrate have previously been dissolved.

After4 hoursthe swollen lentils are separated from the soaking water by sieving and are steam-cooked in an autoclave for 35 minutes. Steam-cooking is performed in the following steps: 5 minutes at normal pressure, 20 minutes at pressures between 1.2 and 1.3 bar and 10 minutes between 1.3 and 1.5 bar.

After cooking the lentils are cooled by briefly (about 5 minutes) allowing them to evaporate and then freezing them in a freezer at -30"C. After a holding time of 16 hours at -30"C the frozen lentils are placed on a hurdle and are dried first at 80"C and then at 50"C airtemperature to a final water content of 6%.

The lentils thereby obtained are ready for consumption, which means that they have been reconstituted in an optimum way and have a tender consistency, when together with a real soup mix containing starch, protein and fat they are moistened with boiling water and are allowed to stand for 5 minutes.

In orderto showthe importance of the use of all measures proposed in this invention in the combina -tion outlined, three comparative tests were run which always strictly repeated the procedure given in Example 1, except for the changes mentioned below: Comparative Test la: No complexing agent (citrate) was used and the cooling (freezing) step omitted.

The lentils thus obtained remain hard when mois tened with boiling water and in a real soup mix may only be prepared for consumption by cooking for 15 minutes.

Comparative Test 1b: No complexing agent (citrate) was used.

As in comparative test 1 a, the lentils thus obtained do not show instant properties and differ merely inasmuch as they need not be cooked as long as that in a real soup mix in order to be brought to a ready to-eat state (cooking time 12 minutes).

Comparative Test 1c: The cooling (freezing) step was omitted.

The lentils thus obtained again do not exhibit instant properties and differ from the lentils obtained according to comparative tests 1a and 1 b only inasmuch as, when cooked in a real soup mix, they reach the ready-to-eat state in a shorter time (cooking time 3 minutes).

Example 2 100 kg white beans (Michigan pea beans) are soaked at room temperature (about 20"C) in 250 liters of tap water in which 7.5 kg tripotassium citrate have been dissolved. After a steeping time of 16 hours the soaking water is removed and the beans are steam-cooked in an autoclave for 55 minutes in the following steps: 10 minutes at normal pressure, 30 minutes at 1.5 bar and 15 minutes at 1.8 bar. After brief evaporation (about 15 minutes) the beans are frozen in a freezer at-30 C and are maintained atthis this temperature for 16 hours. Then they are hurdledried, first at 80"C and then at 50"C. The final water content is 6.3%.

The beans produced in this way also do not need to be cooked in orderto be prepared for consumption. The products are ready-to-eat (in real soup mixes) when moistened with boiling water and allowed to stand for 5 minutes.

Comparative Test2a: No complexing agent (citrate) was used and the cooling (freezing) step omitted.

The beans obtained in this manner remain hard when moistened with boiling water and may be brought to a ready-to-eat state in a real soup mix merely by cooking for 20 minutes.

Comparative Test 2b: No complexing-agent (citrate) was used.

The beans produced in this manner, like those after comparative test 2a, do not show instant properties and differ from these beans merely inasmuch as they need not be cooked as long as that in a real soup mix in order to be ready-to-eat (cooking time 10 minutes).

Comparative Test 2c: The cooling (freezing) step was omitted.

The beans thus produced again do not show instant properties and differ from the beans obtained according to comparative tests 2a and 2b only inasmuch as in the real soup mix they need less time for cooking to a ready-to-eat state (cooking time 5 minutes).

Example 3 100 kg peas are soaked at room temperature (about 20"C) in 250 liters of tap water, in which 7.5 kg tripotassium citrate have been dissolved. After a 16-hour swelling time the soaking water is removed and the peas are steam-cooked in an autoclave for 45 minutes at normal pressure and for 40 minutes at 2 bar. After brief evaporation (about 5 minutes) the peas are frozen in a freezer at-300C and are maintained at this temperature for 16 hours. Then they are hurdle-dried, first at 809C and then at 50"C. The final water content is 6.3%.

The peas thus prepared are ready for consump tion, i.e. they have been reconstituted in an optimum way and are of a tender consistency, when in combi nation with a real soup mix containing starch, pro tein and fat they are moistened with boiling water and are maintained in this mixture for 5 minutes.

Comparative Test 3a: No complexing agent (citrate) was used and the cooling (freezing) step omitted.

The peas thus obtained remain hard when moistened with boiling water and in a real soup mix may only be converted into a ready-to-eat state by cooking for 20 minutes.

Comparative Test 3b: No complexing agent (citrate) was used.

As in comparative test 3a, the peas thus obtained do not show instant properties and differ from the peas in that test merely inasmuch as they need not be cooked in the real soup mix as long as that in orderto be ready for consumption (cooking time 10 minutes).

Comparative Test 3c: The cooling (freezing) step was omitted.

The resulting peas again do not show instant properties and differ from the peas obtained according to comparative tests 3a and 3b merely inasmuch as they need a shorter time for cooking to a readyto-eat state in the real soup mix (cooking time 5 minutes).

Example 4 This example explains a preferred embodiment of the process of the invention for the production of instant dehydrated vegetables from a type of vegetable which has a low starch content and is relatively quick-cooking, i.e. carrots, celeriac or leek.

100 kg carrots, celeriac or leek each are washed, picked, peeled and cut in the usual manner (4 mm cutting thickness for root vegetables) and are then blanched in a steam blancher (peroxidase test negative), introduced immediately into a 2.5%tripotassium citrate solution and cooled therein within about 20 minutes to atemperature below40 C. Subsequently the goods separated from the cooling solution are dried on a hurdle dryer to a final water con tent of 6.5%.

The products produced in this manner do not need a cooking step for being converted into the readyto-eat state. When moistened with boiling water and allowed to stand for 5 minutes, the products are ready for consumption (in real soup mixes containing also starch, protein and fat).

Example 5 100 kg carrots, celeraic or leek each are prepared as described in Example4 and are blanched in a 1% citrate solution and following cooling to a frozen state are directly subjected to freeze-drying.

The products produced in this manner do not require a cooking step in order to be converted into the ready-to-eat state. When moistened with boiling water and allowed to stand for 5 minutes the products are ready for consumption (in real soup mixes containing also starch, protein and fat).

Comparative Test: Instead of being cooled and freeze-dried, the vegetables are immediately dried by circulated air (hurdle dryer) after having been blanched. The products thus obtained require a cooking time of 18 to 20 minutes for conversion into the ready-to-eat state.

Claims (18)

1. A process for producing dehydrated vegetables which can be prepared for consumption by introducing them into a hot, especially boiling, aqueous rehydrating medium and briefly allowing them to stand for no more than about 5 minutes (instant dehydrated vegetables), from fresh or fielddry vegetables or pieces of vegetables by impregnation with an aqueous solution containing at least one substance capable of complexing polyvalent metal ions (complexing agent), especially a citrate, and by drying, characterized in that prior to drying the vegetables prepared in the manner known (a) are optionally soaked in a liquid, aqueous medium, (b) are precooked in a liquid and/or vaporous, water-contaning medium and (c) are cooled to a temperature of about 50"C maximum, with the proviso that at least one of the process steps (a) to (c) is performed in the presence of an aqueous impregnating solution containing the complexing agent(s).

2. The process of claim 1, characterized in that an impregnating solution with a content of complexing agent(s) of no more than about 4.8, preferably no more than 4.0 and especially no more than 3.0% w/w is used.

3. The process of claim 1 or 2, characterized in that the vegetables are soaked and/or cooled in said aqueous impregnating solution.

4. The process of one of claims 1 to 3, characterized in that the vegetables are precooked at elevated pressure.

5. The process of one of claims 1 to 4, characterized in that the vegetables are precooked by heating in steam.

6. The process of one of claims 1 to 5, characterized in that the vegetables are cooled in a liquid, aqueous medium.

7. The process of claim 6, characterized in that the vegetables are cooled in an impregnating solution containing the complexing agent(s).

8. The process of claim 7, characterized in that the complexing agent(s) is (are) incorporated in the vegetables only during the cooling step.

9. The process of one of claims 1 to 8, especially for the production of instant dehydrated vegetables with a high starch content, preferably instant legumes, characterized in that the vegetables which have been cooled and optionally freed from excessive liquid precooking and/or cooling medium are frozen prior to drying.

10. The process of claim 9, characterized in that prior to drying the vegetables are maintained in a frozen state, preferably at a temperature of between about -10 C and -35 C, for a prolonged time, preferably for about 2 to 36 hours, more preferably for about 12 to 24 hours and most preferably for about 14to 18 hours.

11. The process of claim 9 or 10, characterized in that the frozen vegetables are dried or freeze-dried directly, i.e. without previous thawing.

12. The process of one of claims 1 to 11, characterized in that at least one citrate, especially an alkali citrate and preferably a potassium citrate, is used as said complexing agent.

13. The process of one of claims 9 to 12 for the production of instant dehydrated vegetables with a high starch content, especially instant legumes, characterized in that the vegetables are cooked to a ready-to-eat state during precooking.

14. The process of one of claims 1 to 12, espe ciallyofclaim(s) 3,4, 5,6,7,8 and/or9forthe pro- duction of instant dehydrated vegetables with a low starch content, characterized in that the vegetables or pieces of vegetables are merely blanched during precooking.

15. Dehydrated vegetables in pieces with cooking times which have been reduced by incorporation of at least one complexing agent, especially a citrate, in an amount of at least about 0.5% wlw, referred to the dry weight of the vegetables, characterized in thatthey (a) have been precooked in the presence of liquid and/or vaporous water, (b) contain complexing agent(s) in an amount not over 4% w/w, preferably not over 3.5% w/w and especially not over 2.5% w/w, referred to solids, which has (have) been incorporated prior to drying by impregnation with an aqueous solution, and (c) show instant properties, i.e. can be prepared for consumption by introducing them in a hot, especially boiling, aqueous rehydrating medium and briefly letting them stand for no more than about 5 minutes.

16. The vegetables of claim 15, characterized in that they have been produced according to the process of one of claims 1 to 14.

17. The vegetables of claim 15 or 16, character- ized in that they have a high starch content and consist especially of legumes, corn, rice and/or pieces of tubers.

18. The use of dehydrated vegetables of one of the claims 15 to 17 and/or of dehydrated vegetables produced according to one of the claims 1 to 14 in dehydrated soup and/or dehydrated casserole mixes.