GB2251366A

GB2251366A - Improvements in and relating to snack products

Info

Publication number: GB2251366A
Application number: GB9200224A
Authority: GB
Inventors: Jerome Selwyn Selwyn-Smith; Malcolm Stuart Wilkes
Original assignee: United Biscuits Ltd
Current assignee: United Biscuits Ltd
Priority date: 1991-01-04
Filing date: 1992-01-06
Publication date: 1992-07-08
Anticipated expiration: 2012-01-06
Also published as: GB2251366B; GB9200224D0

Abstract

A process for making potato snack products, in which potato slices are immersed in oil that is maintained at a temperature that is not less than the gelatinisation temperature of starch and not greater than 90 DEG C, the temperature of the oil and the period of the immersion being such that starch at and in the vicinity of the surface of the slices is gelatinised, and the oil-treated slices are fried in a continuous fryer at a temperature not greater than 160 DEG C.

Description

Improvements in and relating to snack products The invention relates to a process for the manufacture of a potato snack product. The invention also relates to a potato snack product produced by the process. The invention relates in particular to the sliced-potato snack products generally known as "crisps" in the UK, and as "chips" in the U.S.A. and in certain other countries.

In one previously known process for making potato snack products, potatoes are sliced and the slices introduced directly into a batch fryer filled with oil at a temperature of, for example, 150 C. The slices are prevented from sticking to one another by an operator who stirs the floating slices. Starch that has been freed from the sliced surfaces of the potato falls down through the heating element that is generally present in batch fryers to a region at the bottom of the fryer, which is cooler so that the starch tends not to burn.

The product obtained according to the above process is generally known as "kettle fried" and is dense and hard in texture. The process is, however, expensive to operate because of the need for an operator to stir the contents of the fryer.

Attempts have been made to automate the manufacture of such products by use of a continuous fryer. In a continuous fryer, however, starch that has been released by cutting the potato causes the slices to adhere to one another and, as a result, some portions of the products may be undercooked. Further, the temperature of the continuous fryer is maintained by pumping the oil through a heat exchanger; there is a tendency for free starch in the oil to build up on the heat exchanger elements and to burn and also to reduce the efficiency of the heating elements. It is therefore usual in processes that use a continuous fryer to wash the slices in cold water in order to remove free starch before frying. The product of such processes is softer and less dense than that of the batch frying process described above.

It has not previously been recognised that the cold washing step has any effect on the texture of the subsequently fried product, but it has now been found that, for slices that have been washed for from 1 to 10 seconds, there is a substantial decrease in hardness, the magnitude of the decrease being positively correlated with the length of time of the wash. For slices that have been washed for longer periods, a further, more gradual decrease in hardness with increasing wash times is observed. It has also been found that, on washing the slices in cold water, a rapid weight loss of 3% occurs in the first ten seconds of washing, followed by a more gradual weight loss of 1% over the subsequent five minutes.

It is thought that the initial, rapid weight loss is accounted for by the removal of loose starch grains that have been released by slicing the potato, and that the subsequent, more gradual weight loss is accounted for at least in part by the release of starch derived from cells that have been cut or otherwise ruptured by slicing the potato, but that are so bound to the slice that they are not as readily detachable as the said loose starch grains. Also, during the wash, water enters the cells of the slice by osmosis.

The present invention is based on the observation that both the loss in solids content of the slice and the increase in water content contribute to the softer, less dense nature of the product as compared with a kettle fried product.

The present invention provides a process for making potato snack products, in which potato slices, preferably, raw potato slices, are immersed in oil that is maintained at a temperature that is not less than the gelatinisation temperature of starch and not greater than 90 C, the temperature of the oil and the period of the immersion being such that starch at and in the vicinity of the surface of the slices is gelatinised, and the oiltreated slices are fried at a temperature not greater than 160 C.

The gelatinisation temperature of most potato starches is approximately 63 C and the temperature of the oil will therefore generally be within the range of from 63 C to 90 C. The oil is advantageously maintained at a temperature in the range of from 70 C to 90 C and, preferably, from 70"C to 800C. The temperature of the oil may vary during the immersion of the slices therein, but will at no time exceed 90 and, preferably, will at no time exceed 80 C.

The term "oil treatment" is used herein to denote the process step in which potato slices are immersed in oil that is maintained at a temperature that is not less than the gelatinisation temperature of starch and not greater than 90"C, the temperature of the oil and the period of the immersion being such that starch at and in the vicinity of the surfaces of the slices is gelatinised.

The term "oil-treated" used herein in connection with potato slices denotes that the slices have been subjected to the oil treatment defined above.

Starch at and in the vicinity of the surface of potato slices is starch that has been released from cells that were cut or otherwise ruptured when the potatoes were sliced. In a conventional cold water wash, and in any other treatment similarly involving water, that surface starch is washed away. As indicated above, it is believed that the loss of that starch contributes to the relatively soft, less dense texture of conventional sliced-potato snack products. The oil treatment of the slices according to the present invention has the effect of immobilising the surface starch.

It is thought that an increase in the water content of those cells in the interior of the slice that are not cut or otherwise ruptured as a result of the osmotic flow of water into the cells during the cold water wash also contributes to the relatively soft, less dense texture of conventional sliced-potato snack products. It is believed, for example, that the increase in water content, as compared with potato slices that have not been washed in cold water, could cause a greater amount of expansion on frying, thus creating more voids within the slice that can absorb the frying oil. The oil content of the fried slice would thus be greater, and in consequence the texture would be softer, than that of slices that had not been washed in cold water prior to frying.

Another possibility is that, on absorption of the water, the cells swell so that, on removal of the water as steam during frying, there is a greater amount of space within the cells for absorption of frying oil than would be the case in slices of potato that had not been washed in cold water prior to frying. Once again, if the fried slices contained more oil, they would have a softer texture.

The oil treatment can be carried out at such a temperature and for such a time that starch in the interior of the slices is also gelatinised and hence retained within the slices. It is believed, however, that it is not necessary that starch in the interior of a slice be gelatinised in order to retain within the slice the starch of any ruptured cells in the interior: the gelatinised starch at the surface of the slices minimises the loss of starch and other solids from the interior of the slices.

It is considered that it is the presence in a surface layer of the oil-treated potato slices of starch and other solids that are otherwise lost during conventional water washing procedures that contributes significantly to the desired hard and dense (flinty) texture of the product obtained after frying.

Electron microscopy may be used to observe the surface of a potato slice and to assess the gelatinisation of starch at the surface. The physical state of starch in the interior of a potato slice may be observed by means of light microscopy using a polarising filter, under which conditions "Maltese crosses" are characteristic of crystalline starch. Gelatinised starch does not give rise to "Maltese crosses".

As set out above, the process of the present invention involves oil-treating and subsequently frying potato slices. Potatoes should be cleaned, and may be peeled, if desired, before being sliced. Peeled potatoes may be pre-treated before slicing, for example, by blanching. It will be appreciated, however, that, although whole potatoes may be blanched using hot water or steam prior to slicing, potato slices should not be subjected to treatment with or involving water, especially chemical blanching or the conventional cold washing treatment described above, because such treatment causes loss of starch from the slices. It is advantageous to subject potato slices to oil treatment without any process step interpolated between the slicing step and the oil treatment step, that is to say, it is advantageous to subject raw potato slices to the oil treatment.It is, however, advantageous to convey the cut slices to the oil treatment step by means of a current of oil, advantageously, the same type of oil as used for the oil treatment.

The thickness of the potato slices to be oil-treated is advantageously within the range of from 0.75 to 2.50 mm, and preferably from 1.00 to 1.65 mm.

As stated above, the temperature of the oil in which the potato slices are immersed and the period during which the slices are immersed is such that starch at and in the vicinity of the surface is gelatinised. The greater the proportion of starch at and in the vicinity of the surface that is immobilised by gelatinisation, the harder and more dense the product. As a general rule, the higher the oil temperature the shorter is the period during which the slices should be immersed in the oil.

For production on a commercial scale it is generally preferred to subject the slices to oil treatment for a period within the range of from 20 seconds to 2 minutes.

The oil treatment may be carried out, however, for less than 20 seconds, provided that starch at and in the vicinity of the surface of the slices is immobilised by gelatinisation, or for longer than 2 minutes.

The oil used for the treatment of the slices may be any food-grade oil that is suitable for the production of potato products. It is preferably of the same type as the oil used for the frying step. Examples of oils that may be used for the treatment and/or for frying are sunflower, soya, corn, cottonseed, palmolein and rapeseed oils.

After the oil treatment, the slices may be allowed to drain, or surplus oil may be removed by blowing cool air, for example, air at room temperature, over the slices before the slices are put into the fryer. The oil-treated slices may advantageously be introduced into the fryer without any intervening process step.

The potato slices are fried in a continuous fryer at a temperature not exceeding 160 C. The slices may be fried at a temperature that is not less than 130or, advantageously, not less than 135 C and, preferably, not less than 140 C.

The oil-treated slices may be fried at a constant temperature, for example, the oil in the fryer may be maintained at a constant temperature within the range of from 1300C to 160 C, advantageously, within the range of from 130 C to 150 C or from 140 C to 160 C, and, preferably, from 135or to 150 C or from 150 C to 160 C.

It is advantageous, however, to fry the oil-treated slices in a continuous fryer having an oil temperature profile that decreases in the direction of advance of the slices through the fryer, so that the individual oiltreated slices are fried at a temperature that decreases with time. The initial oil temperature is not greater than 160 C, and the temperature preferably decreases to not less than 130 C, advantageously, the oil temperature may decrease along at least part of the length of the fryer by not more than 20 C, and, preferably, from an initial temperature of 1600C to a final temperature of 145 C, or from 1500C to 135 C.

It is especially advantageous to fry the oiltreated slices in a continuous fryer that has an oil temperature profile that decreases in the direction of the advance of the slices through the fryer from an initial temperature that is not greater than 160"C to a minimum temperature (preferably not less than 130 C) and then rises from the minimum temperature to a temperature at or near the initial temperature. For example, the oil temperature may decrease by about 20 to 30on, for example, 15or, from the initial temperature and then increase to a level that is at or near the initial temperature.For example, if an initial temperature of the oil is 150or, the temperature of the oil may decrease along the length of the fryer in the direction of the advance of the slices to a minimum of 135 C and then rise to a final temperature within the range of from 140 C to 150or, which final temperature may be maintained along the remaining length of the fryer to the point at which the slices are removed. Such a temperature profile may be constructed, mutatis mutandis, for any suitable initial temperature.

In temperature-profile frying methods in which frying is performed in a continuous fryer having an oil temperature profile that first decreases, and then increases in the direction of advance of the slices, the frying period from the start of frying at the initial temperature during the decrease in temperature to the minimum temperature is referred to herein as the first frying stage; frying during the period from the minimum oil temperature and during the rise in the oil temperature to the final temperature is referred to herein as the second frying stage, and frying in oil at the final temperature is referred to herein as the third frying stage.

The frying time for the oil-treated slices is generally within the range of from 2 to 8 minutes. In the case of temperature profile frying the times at the different temperatures are, for example, up to one minute for the first frying stage, four minutes for the second frying stage, and one minute for the third frying stage.

In one form of apparatus for carrying out the process of the present invention, the apparatus comprises means for containing oil and maintaining the oil at a temperature within the range of from the gelatinisation temperature of starch to 90on, means for introducing potato slices into the oil, means for removing the slices from the oil, means for frying the oil-treated slices, means for conveying the oil-treated slices to the frying means, and for introducing the oil-treated slices into the frying means, and means for removing the fried slices from the frying means.

The means for introducing the potato slices into the oil treatment means may be a potato slicer so arranged that the slices produced by the slicer fall from it into the oil treatment means, or may be means for conveying potato slices from a potato slicer to the oil treatment means. A conventional water flume should not be used to convey cut slices to the oil treatment means. Instead, it is advantageous to use an analogous flume in which the slices are transported by oil instead of water. The oil used in the flume is preferably of the same type as that used for the oil treatment.

Advantageously, the oil treatment means is suitable for continuous operation. Such oil treatment means may comprise an elongate container having means for ensuring that the temperature of the oil in the container nowhere exceeds 90 C, means for introducing the potato slices at one end, means for conveying the slices to the other end, and means for removing the slices from the oil at the other end.

The means for introducing the slices and the means for removing the slices may each be any conventional conveyor system. The means for conveying the slices through the oil treatment means may be means causing the oil to flow from the end of the container at which the slices are introduced to the end from which they are removed. Alternatively or in addition, the means for conveying the slices from the one end of the container to the other end may be means arranged to move the slices through the oil, for example, an endless conveyor belt having projections, or paddle wheels. Such conveying means may also assist in immersing the slices in the oil and/or means for immersing the slices may be provided.

Alternatively, the oil treatment means may comprise a drum provided with an internal screw.

The means for removing the slices from the oil treatment means is, for example, a conveyor system that may be provided with means for reducing slippage of the oil-covered slices along the conveyor system as they are removed from the oil. The removal means may be perforated to allow oil to drain from the slices as they are removed from the oil treatment means.

One device may comprise the means for introducing the slices into the oil treatment means, the means for conveying the slices along the oil treatment means, for example, elongate container, and the means for removing the slices from the oil treatment means, for example, one endless conveyor belt, may be so constructed that it can perform all three functions.

The means for introducing the oil-treated slices into the frying means and for removing the fried slices may be as described above for the corresponding means for introducing the potato slices into and removing them from the oil treatment means. Again, one device may comprise both means. In addition or alternatively, one device may comprise the means for removing the treated slices from the oil treatment means and the means for introducing the slices into the frying means.

The frying means is a continuous fryer and is generally an elongate tank containing oil and having means for maintaining the temperature of the frying oil within the required range.

If the fryer is to be operated as a continuous fryer having an oil temperature profile that decreases in the direction of advance of the slices through at least a part of the fryer, as described above, the temperature of the oil in the tank may be maintained at the required temperatures by removing, reheating and recirculating the oil as appropriate via oil output, heating and input means.

Fryers of many designs have been proposed for frying at a constant temperature or with a desired temperature profile. Any fryer may be used provided that the desired constant temperature or temperature profile can be achieved and maintained.

The process of the invention enables a hard and dense product to be obtained using a continuous fryer The invention also provides the possibility of substantially avoiding the problem that arises when free starch adheres to the outer surfaces of the heat exchanger elements.

A further advantage is that, although it would be expected that the gelatinised starch on the surface of the slices would cause the slices to stick to one another, for example, during the frying step, that is not the case, and oil-treated slices according to the present invention do not require continuous stirring during frying.

The process of the invention is also advantageous in that it requires only that potato slices be treated in oil and then fried although, if desired, extra steps can be incorporated, for example, a step in which excess oil is removed from the slices may be included between the oil treatment step and the frying step.

Another advantage of the process of the present invention is that kettle-style sliced-potato products can be produced on plant used for producing conventional sliced-potato products, for example, on a production line comprising a potato slicer, conventional water wash apparatus, a continuous fryer and, optionally, a water flume to convey the cut slices from the slicer to the washer. No change is required to the plant and the only changes required to the operating conditions is to replace the water in the wash and, if present, the flume, by oil, and to maintain temperatures within the limits specified.

The invention provides a practical and economic process for producing a kettle-style sliced-potato snack product on a commercial scale.

The following Examples illustrate oil treatment of potato slices according to the invention: Example 1 Raw potatoes were sliced to give slices of thickness 1.14 mm (45/1000 inch, the cut slices being measured using callipers). The slices were divided into eight batches, each weighing 80g. Each batch was introduced into 5 litres of preheated palmolein oil in a large pan.

The oil temperature in each case was maintained at the stated value for the duration of the treatment. The oil temperature and duration of the treatment for each batch is given in Table I below: TABLE I Batch No. Oil temperature Duration of treatment in C in seconds 1 70 15 2 70 30 3 70 60 4 70 120 5 80 15 6 80 30 7 90 15 8 90 30 At the end of the prescribed time, the slices were removed from the oil and placed in frying baskets. The slices were then introduced into a fryer having two sections, each containing 7 litres of palmolein oil preheated to a temperature of 152 C, and were fried for 180 seconds with occasional stirring.

In each case, the hardness, as perceived by a taster, was found to be very similar to that of a kettle fried sliced-potato product and was significantly harder than a product that had been washed with cold water and had not been oil-treated prior to frying under the same conditions.

Electron micrographs showed that the appearance of the surface of products where the potato slices had been oil-treated and then fried was, in each case, similar to the appearance of products where the potato slices had simply been fried under the same conditions, and had not been washed before frying, but was significantly different from that of a product where the potato slices had been cold-washed with water prior to frying. In particular, in the case of products where the slices had been oil-treated before frying, an opaque layer of starch was visible on the surface of the products. In contrast, in a product where the slices had been cold-washed with water prior to frying, the valleys and peaks of the cell structure at the surface were prominent in the electron micrograph, and a comparable opaque surface layer of starch was not seen.

It will be appreciated that the times and temperatures described in this Example for the oil treatment can be used as such or modified as appropriate for a continuous process. It will also be appreciated that the frying temperature and time described in this Example in connection with a batch frying process can be used as such or modified as appropriate for a continuous frying process. Examples of temperature ranges and temperature profiles for continuous frying are given above.

Example 2 In this Example, potato slices were prepared and fried using an apparatus that was substantially identical to apparatus used for producing conventional slicedpotato products, that is, an apparatus comprising a potato slicer, a water flume, a water wash apparatus, and a continuous fryer, except that the water in the water flume and in the water wash apparatus was in each case replaced by palmolein oil.

Raw potatoes were steam peeled and sliced with an Urschel continuous slicer to give slices of thickness 1.42 mm (the cut slices being measured using callipers).

The slices were transported by an oil flume operating at approximately 35 C to an oil washer having an oil bath containing palmolein oil at a temperature of 75 C. The slices were urged through the oil bath by a helical screw towards an endless conveyor belt, an end of which was submerged in the bath, the upper run of the conveyor being inclined gently upwards out of the bath. The continued movement of the slices by the helical screw also served to reduce the tendency of the slices to stick together. When they reached the conveyor, they were lifted out of the bath on the conveyor. The residence time of each slice in the bath was approximately 30 seconds. The conveyor belt was of a meshed material, thus permitting the drainage of excess oil from the potato slices. When they reached the other end of the conveyor, which was located above the oil bath of the continuous fryer, they dropped into that bath. The average length of time between the removal of a slice from the washing oil and its being deposited in the continuous fryer was fifteen seconds.

The bath of the continuous fryer contained palmolein oil at a temperature of 152 C. The slices were fried for approximately 5 minutes. In that manner there were produced continuously crisps which had a texture, including hardness, that, as perceived by a taster, was very similar to that of a kettle fried sliced-potato product. The perceived hardness was significantly greater than a product that had been washed with cold water and had not been oil-treated prior to frying under the same conditions.

Claims

1. A process for making potato snack products, in which potato slices are immersed in oil that is maintained at a temperature that is not less than the gelatinisation temperature of starch and not greater than 90"C, the temperature of the oil and the period of the immersion being such that starch at and in the vicinity of the surface of the slices is gelatinised, and the oiltreated slices are fried in a continuous fryer at a temperature not greater than 160on.

2. A process as claimed in claim 1, wherein the temperature of the oil in which the potato slices are immersed is within the range of from 70 to 90"C.

3. A process as claimed in claim 1, wherein the temperature of the oil in which the potato slices are immersed is within the range of from 70oC to 80 C.

4. A process as claimed in any one of claims 1 to 3, wherein the oil-treated slices are fried at a temperature within the range of from 130or to 160 C.

5. A process as claimed in any one of claims 1 to 3, wherein the slices are fried at a temperature within the range of from 130 C to 150or.

6. A process as claimed in any one of claims 1 to 3, wherein the slices are fried at a temperature within the range of from 140 C to 160do.

7. A process as claimed in any one of claims 1 to 3, wherein the oil-treated slices are fried at a temperature within the range of from 135 C to 150 C.

8. A process as claimed in any one of claims 1 to 3, wherein the oil-treated slices are fried at a temperature within the range of from 150or to 160 C.

9. A process as claimed in any one of claims 1 to 3, wherein the slices are fried in a continuous fryer that has an oil temperature profile that decreases in the direction of the advance of the slices along the fryer from an initial temperature that is not greater than 160 C.

10. A process as claimed in claim 9, wherein the oil temperature decreases along the fryer by not more than 20 C.

11. A process as claimed in any one of claims 1 to 3, wherein the oil-treated slices are fried in a continuous fryer that has an oil temperature profile that decreases in the direction of the advance of the slices through the fryer from an initial temperature that is not greater than 160or to a minimum temperature and then rises to a temperature at or near the initial temperature

12. A process as claimed in claim 11, wherein the oil temperature decreases by 20 to 30oC from the initial value and then increases to a level that is at or near to the initial temperature.

13. A process as claimed in claim 12, wherein the initial temperature of the oil is 150"C, the temperature of the oil decreases along the length of the fryer in the direction of the advance of the slices to 135"C and then rises to a temperature within the range of from 140 C to 150 C.

14. A process as claimed in any one of claims 1 to 13, wherein the slices are fried for a period within the range of from 2 to 8 minutes.

15. A process for making potato snack products, substantially as described in Example 1 or Example 2 herein.

16. A potato snack product made by a process as claimed in any one of claims 1 to 15.

17. The use of gelatinisation of starch at and in the vicinity of the surface of a potato slice to immobilize starch in the production of kettle-style crisps in a continuous fryer.