GB2279860A

GB2279860A - Vegetable crisps

Info

Publication number: GB2279860A
Application number: GB9314494A
Authority: GB
Inventors: David Dorricott; Paul Gayler
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-07-12
Filing date: 1993-07-12
Publication date: 1995-01-18
Anticipated expiration: 2013-07-12
Also published as: GB2278038A; GB2279860B; AU695172B2; GB2278039B; GB2278039A; GB9413822D0; AU7128694A; GB2278038B; GB9413823D0; GB9314494D0; WO1995002336A1

Description

2279860 VEGETABLE CRISPS The present invention relates to vegetable crisps

and to a method for their production.

is The production of potato crisps is well known and well explored. There are however particular production problems relating to potato crisps relating essentially to the high proportion of starch in the potato product. For this reason various chemicals and other methods of blanching are required, and primary/secondary and indeed even tertiary drying steps are utilised in order to provide a desired product. Such numbers of drying steps are unnecessary and indeed counter-productive when vegetable crisps formed of materials other than potatoes are to be produced.

In GB-A-2099279 there is described the production of savoury crisps made by frying thin slices of raw carrot for less then 2 minutes in an edible oil at about 185'C. Such a product is satisfactory when first made, but tends to take up moisture from the air and become flacid unless stored in really dry conditions.

The present invention has a first object therefore the provision of vegetable crisps formed from one or more vegetables which have a good taste and maintain their friability for a considerable period.

1 A second aspect of the invention provides means whereby fried vegetable products can be given a more certain shelf-life by heat curing of the fried product prior to packaging. Further a good quality comestible product can be produced without any additives other than the vegetable material and the cooking oil.

is According therefore to a first feature of the present invention there is provided a method for the production of a vegetable crisp which method comprises finely slicing a vegetable matrix, drying said finely sliced vegetable matrix at an elevated temperature over an extended period below the temperature at which the constituent cells thereof become denatured, cooking said dried vegetable matrix in a refined cooking oil at a temperature between 9T to 10CPC for 5 to 20 seconds, allowing the fried vegetable product to cool and subsequently heat curing said cooked vegetable product at a slightly elevated temperature for an extended period; for example at least 8 hours.

In a further aspect of the invention there is provided a vegetable crisp formed from a finely sliced vegetable matrix and fried in a vegetable oil at a temperature of 90P to 120(t for 5 to 20 seconds and subsequently cooled, said crisps being characterised in that said finely sliced vegetable matrix is pre-dried at an elevated temperature for an extended period below the temperature at which the constituent cells thereof become denatured. Preferably the cooked product is subsequently subjected to a heat curing step wherein said cooked vegetable product is I 2 maintained at a slightly elevated temperature for an extended period, for example at least eight hours.

In an alternative method in accordance to the present invention there is provided a method for the production of a vegetable crisps which comprises finely slicing a vegetable matrix, frying said vegetable matrix in a cooking oil at a temperature of 300' to 350'F for a period of 70 to 150 seconds and cooling said cooked product, characterised in that the cooked product is subsequently subjected to a heat curing step wherein said product is heat cured at a slightly elevated temperature for an extended period. Preferably the cooking oil is a refined vegetable oil.

The vegetables to which the methods in accordance with the present invention may be applied include:Beetroot, Plaintain, Swede, Turnip, Celeriac, Sweet Potato, Carrot, Lotus Root, Eggplant, Courgette, and Parsnip.

3 It will be appreciated that the precise conditions ideal for each vegetable matrix will depend on the original moisture content, the particular stock, the thickness of the slices etc. In an ideal arrangement the slices are about 2mm in thickness.

is Where pre-drying of the product is practised it is desirable to dry at an elevated temperature of 2Y to 350C for a period between 10 and 20 hours thereby to reduce the moisture content by 60 to 95% of the original picked vegetable weight without cell wall dislocation.

Although we do not wish to be held to any particular theory, it is believed that the pre-drying method alluded to above is advantageous because it reduces moisture without destruction of the cell walls. When slices 2mm thick are subjected to gentle drying the moisture is relatively easily removed and the vegetable matrix tends to shrivel. When the shrivelled vegetable matrix is placed in cooking oil at about 1OTC the beat gradient set up through the vegetable matrix is initially tenuous such that hot oil initially penetrates the matrix in part by absorption, and in part osmotically by virtue of large moisture deficit. The result is that more oil is taken up into the matrix thereby ensuring that it is fully cooked relatively quickly.

Subsequent to this step the invention also provides a slow heat curing method at a slightly elevated temperature which has the effect of beneficially affecting shelf life. In said heat curing method the cooked products, having had the fat drained from them, are held on an absorbent surface for at least eight hours and preferably 4 1 hours at a temperature between 200 and WC. Holding the product for such a period at a slightly elevated temperature before packing ensures a high qualify product which remains friable over a significant shelf life.

is As specified above, an alternative method of production in accordance to the present invention relates to the wet frying of vegetable matrix of the general type described in the GB-A-2099279. Again a heat curing step applied subsequently provides an advantageous way of ensuring a high quality product with good shelf life. This is particularly desirable in the case of a wet fried vegetable matrix since the final moisture content of such a product tends to be higher than in the other process.

The invention will now be described, by way of illustration only, with reference to the following examples.

Example 1 - Production of vegetable crisps including pre-drying.

Vegetables were selected for the following:- Beetroot, plantain, swede, turnip, celeriac, sweet potato, carrot, lotus root, eggplant, courgette and parsnip. In each case the vegetables were peeled and excess moisture removed in the usual way. Fine slices of the vegetables (hereinafter referred to as the vegetable matrix) were then cut to a thickness of about 2nim. Q/16in) and each form of vegetable matrix was then laid out separately on trays lined with absorbent parchment. The trays were then placed in a drying cabinet at approximately 28.5t for about 15 hours is depending upon the vegetables used. It will be appreciated that the drying time required for a vegetable such as plantain is shorter than that required for a vegetable such as a courgette, although the drying times are not that different because the matrix of a courgette renders up moisture that much more easily than the matrix of plantain. Simple trial and error however gives ideal drying times for each type of vegetable. It is important the temperature of the pre-drying step does not exceed the temperature at which the cell walls of the vegetable matrix are significantly impaired.

When the vegetable matrix has been dried and dehydrated, pieces tend to be somewhat shrivelled in appearance but are ready for frying. In this condition the matrix may be stored in suitable sealed bags. This is convenient when for example it is desired to delay frying over a weekend.

The frying step is effected in a refined good quality vegetable oil at a temperature of 100P to 1059C for 5 to 15 seconds. Again the precise length of time will depend upon the vegetable matrix concerned. However for example the following is a guide: Beetroot crisps Turnip crisps Plantain crisps Sweet potato crisps Celeriac crisps seconds 8 seconds 15 seconds 12 seconds 10 seconds 6 11 When the frying step has been completed the cooked vegetable crisps are removed is from the oil and all excess oil is removed. This may be effected on a small scale by utilising a slotted spoon and placing the vegetable crisps on fresh grease proof parchment or by other methods known in the art. Since the vegetable crisps are at this time somewhat fragile care has to be taken until they crisp up after being removed from the oil. After cooling the crisps are tested for friability and may be returned, if necessary, for further frying should this be necessary.

The vegetable crisps are then subjected to a beat curing step overnight at a temperature between 20" and 300C and are then packaged in a dry container such as an air and moisture resistant food grade plastics container or bag.

It is found that after some weeks the vegetable crisps including for example beetroot, turnip, plantain, sweet potato and celeriac are friable, good to eat, and contain no excess salt.

Example 2 - Vegetable crisps produced by the wet frying method.

A vegetable matrix extracted from beetroot, plantain, swede, turnip, celeriac, sweet potato, carrot, lotus fruit, eggplant, courgette and parsnip are selected according to season and subsequently peeled. The peeled vegetables are then sliced into 2mm (1116in) neat rounds and kept separate from each other and particularly other vegetables to avoid staining. Each batch of sliced vegetable is then cooked 7 by frying in a refined vegetable oil at a temperature of 3201F for a length of time depending upon the vegetable used.

For example the following frying times are given for crisps of 2mm in thickness at 320'F:

Beetroot 120 seconds Turnip 90 seconds Plantain 130 seconds Sweet potato 80 seconds Celeriac 130 seconds is Values at 20% above and below this figure are also useful. Obviously these timings will change depending upon the initial moisture content of the vegetable etc. When cooking has been effected the vegetable crisps so formed are removed from the oil and all excess oil is drained off. The vegetable crisps are then placed on a flat surface and allowed to cool and tested for crispness. They may subsequently returned for a few seconds longer in the frier if they are not crisp enough, but when judged crisp they are allowed to dry overnight in a heat curing step at a temperature between 20 and 3TC. Between 8 and 15 hours is long enough for this heat curing step. The heat curing step ensures a good shelf life for the Product and is particularly important in the case of the wet frying method because, relative to the method incorporating a pre-drying step, the product of the wet method incorporates a higher percentage of moisture.

8 The particular parameters of the processes are set out in the attached Tables 1 to 3 as follows:

9 TABLE- 1

YEILD OF COOKED PRODUCT FROM WET SLICED VEGETABLES (i.e. COOKED SHORTLY AFTER SLICING) Vegetable

Beetroot 410g Plantian 485g Celeriac 4335g 1 Turnip 44og -- 1 Sweet Potato 460g Peelings Veg. weight Fried Driing Length Final wet sliced weight temp. of time weight - cooked to dry 1109 J295g 18 % 55g 72-29C 55 min 55g 230g 250g 50% 0 min 125g 125g (not needed) I log 310g 25% 75g_.j 7?-.-?'C 20 min 75g I log 3 320g 18% 65g 1772.2"C 25 min 65g 85g 370g 28% 140g 7 2. 2 0 C 0 min 140z (not needed) 11.

TABLE 2

WET FRYING METHOD Vegetable weight (Wet) of vegetables 500g Beetroot Turnib - 500g Plaintain weet Potato Celeriac 500g 500g 500g Frying Titne Frying Temp. Finished crips weight 2m 320'J7 105g I m 30sec 320"F 105g 2m 10sec 320'F 280g J. in 20 see 3AfF 330g 2m 10sec 320'T 130g TABLE3

DRY FRYING METHOD Vegetable Prepared weight Beetroot 500g - Turnip 500g Plantain 500g Sweet potato 500g 1 Celeriac 1 500g Dried - weight 60g - A Drying time hours Drying Frying temp. time _ 15 43g 185g 120g c 60g is 285C 285'C 8sec 2850C 15sec 2850C 12sec 10sec 1 Osec Fng temp.

11 OOOCC Finished weight -- -1 10011C Wc 00 Esec-11 1000C 1000C 1000 85g 75g 200g 145g 85e C\J 13

Claims

CLAIMS to 0 00 1. A method for the production of a vegetable crisp which

method comprises finely slicing a vegetable matrix, and either drying said f inely sliced vegetable matrix at an elevated temperature over an extended period below the temperature at which the constituent cells thereof become denatured, and cooking said dried vegetable matrix in a refined cooking oil at a temperature between 900C and 1000C for 5 to 20 seconds; or cooking said vegetable matrix in a cooking oil at a temperature of 1500 to 1800 for 70 to 150 seconds; and allowing the cooked vegetable product so produced to cool and subsequently heat curing said cooked vegetable product at a slightly elevated temperature for an extended period.
2. A method according to Claim 1 wherein the extended period of the heat curing step is at least 8 hours.
3. A method according to Claims 1 or 2 wherein the vegetable - product does not include the potato.
4. A method accord ing to any preceding Claim wherein the vegetables are sliced to about 2mm.
5. A method according to any preceding claim wherein the vegetable matric is predried prior to cooling by treatment at a temperature of 250C to 350C for 10 to 20 hours thereby to reduce the moisture content by 60% to 95% of the original weight.

A vegetable crisp produced by a method as claimed in any one of claims 1 to 5.

01

5. A method according to any preceding Claim wherein the vegetable matrix is predried prior to cooling, and is treated at a temperature of 250C to 350C for 10 to 20 hours thereby to reduce the moisture content by 60% to 95% of the original 3 0 weight.

6. A vegetable crisp produced by a method as claimed in anyone of Claims 1 to 5.

1+ Amendments to the claims have been filed as follows A method for the production of a vegetable crisp which method comprises:f inely slicing a vegetable matrix, and drying said f inely sliced vegetable matrix at an elevated temperature over an extended period below the temperature at which the constituent cells thereof become denatured, and cooking said dried vegetable -matrix in a ref ined cooking oil at a temperature between 900C and 1000C for 5 to 20 seconds; allowing the cooked vegetable products to cool and optionally subsequently heat curing said cooked vegetable products at an elevated temperature for an extended period.

2. A method according to claim 1 wherein the extended period of the heat curing step is at least 8 hours.

3. A method according to claims 1 or 2 wherein the vegetable product does not include the potato.

6.

1 4. A method according to any preceding claim wherein the vegetables are sliced to about 2mm.