GB2178292A - Process for the artificial drying of uncooked dough products - Google Patents

Abstract

Process for the artificial drying of uncooked dough, in which the temperature of the dryer in the first phase after the commencement of drying is kept above 100 DEG C and, at the same time, the humidity of the dryer is regulated in such a manner that its lower value is at most 5%, but preferably from 2 to 4%, lower than the current relative equilibrium humidity of the drying uncooked dough, and then in a further, second phase, the temperature and the humidity of the air in the dryer are reduced together in such a manner that the lower value of the relative humidity becomes at most 8%, preferably from 4 to 8%, lower than the current relative equilibrium humidity of the drying uncooked dough.

Description

SPECIFICATION Processforthe artificial drying of uncooked dough products The invention relates to a process forthe artificial drying of uncooked dough products.

As is known, the manufacture ofdryfarinaceous products (macaroni, spaghetti, pasta spirals, egg barley) can basically be divided into two main phases.

These are the manufacture ofthe uncookeddough in a suitable shape and then the drying process.

The basic material of dough production is the flour, which is in many respects different from the flour used in a bakery. For the manufacture of ground products forthe dough industry there are suitable only varieties ofglasswheatthatallowtheproducion of uniform, coarse-grained, bran-free semolina orflour and contain a large amount of tough, resilientgluten of good quality. Thetypes ofsemolina groundfrom glass wheat (triticum durum) are most suitable for these purposes. The gluten of glass wheat is particularly tough and resilient.In the case of the techniques known hitherto,the amount and quality ofthe gluten are of crucial importance to the qualityespeciallyto the cooking and mechanical properties- of dry farinaceousfood.

The gluten content of other ground wheat products is generally lower, and also the quality is unfavourable for dough production.

Th e g ranu lar structure of glass wheat allows the production of a ground product having a grain size of from 250 to 400 um, and this can advantageously be usedforthe production of dough.

None of the other types of wheat (triticum aestivum) has all ofthe described quality characteristics.

ltthereforefollowsthatthequality of dryfari- naceousfoods consisting of flour of aestivum wheat do not attain the quality of farinaceous foods consisting of ground durum products; the mechanical properties ofthe end products are likewise unfavourable.

The crop yield of glass wheats is significantly lower than that of aestivum wheats; furthermore, it is primarily the areas having a Mediterranean climate that are suitable for the production of glass wheat. For this reason the price of ground durum products is significantly higherthan that of ground aestivum products.

The main phases in the preparation of dryfari naceousfoods are as follows: - preliminary preparation ofthe raw materials, - stirring (preparation of the farinaceous food), -compacting, - shaping, -drying.

As is known, the purpose of drying farinaceous food products isto provide the product with qualities such that the product will withstand mechanical working during furthertreatment and will not act as a nutrient medium for the growth of microorganisms. The drying offarinaceous food is an operation requiring very careful consideration and specialist knowledge, and the manner in which the operation is carried out is crucial to the quality ofthe product. It is generally thoughtthatthe drying offarinaceous food is a very simpletask, butthis is notthe case.In particular, the drying offilamentary products represents a special and demanding task, especially because of the exact adjustmentofthetemperature and the relative humidity that is necessary throughout the drying operation.

The original, that is to say the simplest, method of dryingfarinaceousfood is drying in the natural surroundings or in the open air. This method was used especially in the Mediterranean regions where most of the air currents flow from the sea towards the land, so the the drying is carried out in air having a correspondingly high relative humidity. Because ofthe high humidity the drying takes a long time in the order of days. During the drying, when the water has evaporated from the surface layer of the product, the product is taken into a room that is from 12to 15 cooler, generally into a cellar. The product is kept here for8to 10 hours, a uniform distribution of moisture being obtained in the product. It is then taken into the open air again, and surface drying follows.These operations are carried out untit the water content of the product is approximately 12-13%. This process generallytakes several days. In the construction of artificial drying apparatus, special efforts were made to shorten the drying time while maintaining the qualityofthe product. Forthis reason, a slow, careful reduction in moisture is considered to be important in drying techniques. Therefore the drying time in the case offilamentary products was from 48 to 72 hours and in the case of small products from 24to 36 hours.

The maximum drying temperature was 30 to 320C and later 40 C. The relative humidity was kept at a value between 65 and 75%.

The drying devices according to these techniques were manufactured until the 1950s. Subsequently lines producing completefarinaceous foods began to be used, these lines being fully mechanised continuous lines and being provided with modern measuring and regulating apparatus. In the drying apparatus there is carried out a so-called pre-drying operation in which the farinaceous food introduced into the dryer is gradually heated from an initial temperature of 28-30'C to a temperature of 48-50"C.

The humidity of the air is 80-85% andthethroughput time forthe farinaceous food is 50-70 minutes. The water content ofthe farinaceous food passing into the pre-dryer is 30-32% and the water content ofthe farinaceous food being discharged is approximately 22-23%.The nextphase isthefinishing to equalisethe relatively high moisture gradients and the stress in the farinaceous food. The temperature in this phase is 60-65" and the relative humidity is 90-95%. The throughput time, that is to say the finishing time, is from 20to 60 minutes.

The next phase, or the end phase, ofthe process is the so-called final drying. The temperature in the apparatus is approximately 55"C on entry and this is gradually reduced to 35-300C. The relative humidity is reduced from 85-90% to 72-76%. In the case ofthis drying apparatus operating continuously, the total drying time-together with the pre-drying - is from 25 to 30 hours depending upon the product. These devices are still used today as industrial production units having large capacity.

The aim offurtherdevelopment in farinaceous food production was the further reduction ofthe through- puttime (drying tiem), and this was achieved by increasing the humidity and the temperature. These dryers have been used as industrial apparatus since the beginning ofthe 1 970s. They are distinguished by the factthatthey are also provided with a pre-dryer and a final dryer. Theflow rate of the drying air is 8 - 10 m/s in the pre-dryer.The heating ofthe air begins as early as at the entry point of the farinaceous food and is gradually increased form 30"C to 60"C. The relative humidity ofthe air is 85-90% inthepre-dryer.The throughputtime is approximately 50-70 minutes; during this time the water content of the farinaceous food is reduced from an initial value of 30% to approximately 18%. This is followed bythefinishing, which lasts approximately 20-30 minutes, at a temperature of 65-70"C and at a relative humidity of 95-98%.

Here too, the final phase ofthe process is the final drying; thetemperature ofthe air is initially 65-70"C, then is slowly reduced and in the last 4to 5 hours of drying is approximately 30"C. The relative humidity is approximately 85-90% atthe beginning ofthe operation, and is then gradually decreased to 75-80%. In this case the drying time is from 18 to 24 hours, depending upon the product Although the above-described solutions allow the production offarinaceous a food of high quality, they have the following disadvantages: -farinaceousfood production requires a granular flourofvery high quality (special flour having a high gluten content).This presents ever greater problems, because products ground from modern types of wheat having a high crop yield are completely unsuitableforthis purpose. The crop yield ofthe durum wheats that are suitable forthe farinaceous food industry is low; the grinding of such wheat requires a special technique. Furthermore, the storage ofthe ground products should also betaken into consideration.All this makes the most important basic material offarinaceousfood production-theflour- too expensive; -the drying time is stiil approximately 20 hours even in the most modern apparatus: with regard to production lines of large capacity, dryers having very large dimensions are used; - because of the relatively high temperature, which is usedfora shorttime, inthe mostmodern apparatus the germ count in the products is significantly reduced; however, even in this case infection can occur during drying, particularly in apparatus at a lowertemperature.

The most important aim ofthe invention is the development of a process for drying uncooked dough which can be realised industriallyandwhich enables the quality requirements with regard to the basic material to be reduced, that is to say that, as a result, ground products from modern wheats having high crop yields are also suitable forfarinaceous food production.

Another aim of our invention is significantly to reduce the drying time, and therefore the size ofthe dryer, so that production costs are reduced.

Afurtheraim ofthe invention is reliablyto avoid an increase in the germ count during drying,that is to say to avoid infection oftheflour.

The invention is based on the recognition that all the above-described aims can be achieved if the drying temperature, unlike the drying temperature in the previous drying processes, is increased to above 1 00'C in the first phase ofthe drying time, and the relative humidity during drying is maintained art a level onlyslightly lower, a maximum of 5% lower, than the current relative equilibrium humidity ofthe farinaceous food to be dried.

The expression "current relative equilibrium humidity ofthe farinaceous food" meand the relative humidity of airthat is equilibrium with the amount of water currently in the food, that is to say, the relative humidityoftheairatwhichthewatercontentofthe food neither increases nor decreases.

This recognition is surprising because according to previous experience in the farinaceous food industry, the drying cannot be carried out above 100'C without causing very considerable damage to the product, for example crack formation and decomposition, because, as a result of the very high moisture gradients occurring on the action ofthe high temperature, excessive mechanical stresses occur in the drying or dried farinaceous food.In the drying processes, therefore, not only was the use of temperatures above 1 00'C avoided but also the use oftemperatures above 70"C. In contrast, we have found thatthe use ofthe temperature above 1 00'C is not damaging if the relative humidity is adjusted in the manner described above, and, in addition the problems posed above can be solved. This will be explained in the following.

The invention therefore relates to a process forthe artificial drying of uncooked dough products in a dryer wherein, after an advantageous introduction phase of the drying, the temperature of the dryer in the first phase is at above 1 00'C and, at the same time, the humidity ofthe air in the dryer is regulated in such a mannerthat its lowervalue is a maximum of 5%, but preferably only from 2 to 4%, less than the current actual equilibrium humidity ofthe drying farinaceous food,then in afurther(second) drying phasethe temperature and the relative humidity ofthe dryer are reduced together in such a mannerthatthe lower value ofthe relative humidity becomes a maximum of 8%, preferably from 4to 8%, lowerthan the current relative equilibrium humidity of the drying farinaceous food.

Uncooked dough isto be understood as meaning the intermediate product which is generally prepared afterthe preliminary preparation ofthe raw materials bystirring, that is to say by preparation ofthe dough; this is generally followed by compacting and shaping.

The water content is approximately 25-30% before drying. As a result ofthe drying operation the water contentofthe intermediate product should be reducked to 12%. The uncooked dough dried in this manner is the product sold as dried farinaceous food.

The introduction phase of the drying process according to the invention is to be understood as meaning the introduction ofthefarinaceousfood into the drying chamber. Atthis stage, the use ofthe temperature above 1 00'C is not yet advantageous but a lowertemperature of approximately 80"C is used in the dryer. The critical first phase according to the invention preferably lasts approximately 1/3 of the total drying time, whilst the temperature is above 10000 and the humidity is regulated in the manner described above. Reducing this time, for example to below 1/4 of the drying time, or extending this time to a significant extent, for example towards 50% ofthe drying time, does not achieve the desired result.

However, the time period of 1/3 should not be regarded as rigid, becausethetime period used in practice depends upon the actual water content of the uncooked dough introduced and upon the type of dough.

Although we have mentioned atemperature of above 10000 in the first phase ofthe drying, this has its reasonable limits; it is not advantageous to raise the temperature in the dryer to above 120-125 C, because this has no advantage, and in fact certain disadvantages can occur, for example a discoloration with a slightlyyellowand brown tinge as a result ofthe superficial dextrineformation.

In the second phase ofthe drying process according tothe invention thetemperature in the dryer should be reduced. This reduction in temperature should prefer abiy be carried out gradually; the temperature ofthe dryer should finally be reduced to 75"C and accordinglythe moisture content should also be reduced in such a mannerthatthe relative humidity of the dryer is always a maximum of only 8%, but preferably from 4 to 8%, lowerthan the relative humidity according to the current equilibrium humidity ofthedrying farinaceousfood.Coolingto 75"C is a minimum requirement and it is possible to cool to lowertem peratu res, in practice generally to approximately45-5000, naturally with a simultaneous reductioninthe relative humidity. These lower temperatures are also associated with humidity content values according to the current equilibrium humidity- as has been described above.

The characteristic values for the relative equilibrium humidity ofthe farinaceous food having differing water contents -- at average moderate temperatures (50-80"C)--are shown inthefollowingtable: Water content in relative equilibrium the dough content % % 10.0 40 11.5 47 12.5 53 13.0 56 13.5 60 14.5 67 15.5 71 17.5 77 18.5 80 20.0 85 22.5 90 29.5 99 Higher or lowertemperatures produce slightvariations in these values.

According to the Table, for example, the current relative equilibrium humidity ofthe dough is 85% at a water content of 20%, but in a dough having a water content of 10%, the current relative equilibrium value is 40%.

During the process it is possible to use a dryer having an intermittantworking action, into which the uncooked dough is introduced and in which the alteration in temperature and humidity is basically carried out in the vicinity of the dough. It is better, however, to use a dryer having continuous operation, that is to say a drying apparatusin which the drying uncooked dough is in motion and the dough is dried by being passed through zones in the dryer having differenttemperatures and different humidities.

A heating device known perse is used to produce the required temperature, and the regulation of the relative humidity of the dryer is effected byventilation or by the addition of steam. Automation is advantageous because of the reliability of the technology. Duringthisautomation it is advantageous not only constantly to measure the temperature and the relative humidity and to regulate them accordingly, but also constantly to measure the water content ofthe dough and to use this value too during the regulation. In this manner the desired technological parameterscan be ensured.

Numerous solutions are known perseforthe measurement and regulation of the temperature. The humidity can be measured or regulated, for example, using the sensor described in HU-PS 179324, with which it is possible to measure the water content of the uncooked dough dietectrically and the signals from such a measuring device can be used for regulation.

As already mentioned, ventilation is also a means of regulation. It is advantageousto limit the flow of air in the dryer, forexampleto usean air speed of 2-4 m/s; and for producing the desired humidity of the air, for example, to compensate fora lowhumidity value, the addition ion of steam can be used or, in the case of an excess of moisture, a moisture collector known perse or another method of reducing humidity (for example using chemical means) can be used.

The advantage ofthe invention lies in the factthat, unlike previous processesfordryingfarinaceous foods, the process according to the invention makes itpossibleto produce dryfarinaceousfoodsof excellent quality, even from flour products of mediocraquality. This is also a result of the factthat during the drying process there is a continuous diffusion of moisture from the inner layers of the dough towards the surface and, as a consequence, the average water content of the substance is reduced from an initial 25-30% to 12%. Asthe drying temperature is increased to 10000 the diffusion rate of the moisture increases significantly especially in a dough having an extremely high water content. The humidity ofthe air in the dryer is kept in a state corresponding to the dew point of 98"C; as a result, no high moisture gradient occurs in the dough, and the formation of cracks and also the tendency towards crackformation is avoided.

The process according to the invention even has a favourable effect on the structure ofthe dough. In the doug h the g rains of starch aggluinateas a result of the action of heat and encapsulate the protein component, and this increases the stability ofthe farinaceousfood, improves the cooking properties to a great extend and even reduces losses during cooking. During the high temperature drying process the protein components are retained which likewise serves to stabilise the farinaceousfood, and as a result loss during cooking is further reduced. All these changes can be verified on microscopoic examination ofthe farinaceous food.The following Table shows a comparison between the cooking properties ofthefarinaceousfood according to the process of the invention and thefarinaceous food according to previous processes.

Cooking features of pasta samples Time of Control Samples cooking (minutes) Swelling (%) Cooking features Swelling (%) Cooking features 5 120 Uncooked, flour/stripe 115 Uncooked in the middle 10 149 Floury stripe still exists 768 Cooked, good substance, smooth surface, no floury stripe 15 181 No flour stripe, sticky 176 Good substance, smooth surface surface, smooth, crumbling structure 20 215 No change 181 Good substance, smooth, surface not sticky 25 221 No change 187 Good substance, slightly sticky surface 30 235 Rather soft, strongly 191 No change crumbling structure Cooking remainsx (%) (losses) 7.58 4.36 x Time of cooking is 12 minutes A furtheradvantage ofthe processaccording to the invention for drying uncooked dough isthat, in comparison with the known drying processes, the drying time is significantly reduced, since the drying time of 18 to 20 hours that can be achieved by artificial drying methods can be reduced by the process ofthe invention to approximately one third, that isto say to 6to8 hours. The reasonforthis is that atthe high temperature used when the uncookeddough is in its wetteststatethe diffusion of moisture isverymuch accelerated, but, because ofthe exactly regulated humidity of the air no moisture gradient occurs, and therefore the quality of the farinaceous food is not impaired.

Another advantage of the process according to the invention lies in the factthatthe risk of an increase in microorganisms is virtually ruled out because of the high germ count and the temperature of 1 OO"C that is used. This also means that, unlike previous processes, it is possible to produce an end product having a iow germ content.

An additional advantage of the method according to the inventionisthat, even when the dough is preparedfromflourhaving high polyphenol oxidase activity, the characteristic brown colour does not appear at all in the end product. This can be explained by the factthat the mentioned enzyme activity virtually ceases because of the high temperature.

The accelerated process also has the advantage that the dryer requires considerably less space.

Relatively small dryers can therefore be used to dry amounts of farinaceous food that in previous processes required dryers approximately three times larger, and, for example, in continuous operation, the dryers can operate with aconsiderably greater capacity if provision is made for the appropriate temperature and the regulation of the humidity.

The process according to the invention can be used for all types and sizes of farinaceous foods.

The invention will be illustrated in more detail with reference to an embodiment which is not, however, intended to limit our invention.

EXAMPLE Uncooked macaroni prepation is introduced into a dryer underthetemperature and humidity conditions given below. Using the process according to the invention,the preparation can be dried as follows: Time dry temperature moist temperature (minutes) "C "C Introduction 80 60 10 100 85 15 118 98 30 100 95 60 100 92 60 92 84 60 88 80 60 84 76 30 83 75 25 82 72 60 80 70 60 78 68 30 75 64 Removal The duration of drying according to the above described process is approximately 500 minutes. The cooking properties ofthe end product produced are compared with the controi product according to previous processes in the previously given Table.

The dry temperature is to be understood as meaning the actual temperature of the dryer, and the moist temperature as meaning the value ofthe temperature indicated in the dryer by a wet thermometer. This latter value is suitablefor indicatingthe humidity ofthe dryer.

Claims (9)

1. A process for the artificial drying of uncooked dough,whereinthetemperature ofthe dryer in the first phase afterthe commencement of drying is kept above 1000C and, at the same time, the humidity of the dryer is regulated in such a mannerthat its lower value is at most 5%, but preferably from 2to 4%, lower than the current relative equilibrium humidity ofthe drying uncooked dough, and then in afurther, second phase, the temperature and the humidity of the air in the dryer are reduced together in such a mannerthat the lower value ofthe relative humidity becomes at most 8%, preferably from 4 to 8%, lower than the current relative equilibrium humidity ofthe drying uncooked dough.

2. A process according to claim 1,whereinthe duration ofthe first phase is approximately 1/3 ofthe total drying time.

3. Aprocessaccordingto claim 1 or2,whereinthe temperatureandthe relative humidity of the dryer in the second phase are gradually reduced at least to 75"C and to the associated humidity.

4. A process according to claim 3, wherein the temperature in the second phase is reduced to 45 to 50"C, and the relative humidity is adjusted to that associated with thattemperature.

5. A process according to any one of claims 1 to 4, wherein the drying dough in the dryer is kept in motion, so thatthe dough is first introduced into the zone having a temperature of above 100 C and from there is gradually transferred to zones having lower temperatures.

6. A process according to anyone of claims 1 to 5, wherein the relative humidity in the dryer is regulated by ventilation and/or by the addition of steam and/or bycondensation of moisture.

7. A process according to claim 6, wherein the relative humidity in the dryer is adjusted with the aid of an automatic regulator.

8. A process according to any one of claims 1 to 6, wherein the automatic regulation of humidity is carried out also in dependence upon a value derived from the measurement of the water content ofthe drying dough.

9. A process as claimed in claim 1 substantially as hereinbefore described in the Example.