Steam Peeling  -  Mechanical Peeling in Small-scale, Medium-sized and Large-scale Industrial Enterprises

- Where to Apply which Peeling Methods?

The functioning of peeling methods

During steam peeling the fruits to be peeled are exposed for a short time to high temperatures in a pressure vessel. After that, the nearly loose skins are abraded and/or washed off by means of other machines connected behind. The surface of the peeled fruit is smooth. However, this surface layer consists of a "cooking ring" which is more or less thick, due to the short but intensive heat effect. This "cooking ring" (appr. 2-4 mm deep) consists of the parboiled, "half-cooked" layer, i.e. this layer is not raw anymore.

On mechanical peeling the skins of the fruit are abraded by means of rough or fine carborundum granulation or by a blade peeling machine with blades. "Cooking rings" are avoided. The surface of the peeled fruits can have - depending on the carborundum granulation - a rough or very smooth appearance. - Mechanical peeling is carried out in continuously working "roller peeling machines" or in so-called "batch peelers". In case of cutting with blade peeling machines a smooth blade cut results.

Application fields of steam peelers

On account of the high investment costs (a steam generator is required, too), steam peelers are generally used in Western Europe, if large quantities of fruits (from 7.5 to 20 tons/hr) have to be peeled, with little floor space being available. But this method is chosen only in those cases where the "cooking ring" is irrelevant for the quality of the final product.

This "cooking ring" is unacceptable for the potato chips industry (GB: crisps), because it affects the appearance of the final product. That's why one works with mechanical peelers in the potato chips industry, whereas the French fries producers (GB: chips) use steam peelers if high throughputs are required.

Steam peelers are also preferred for difficult small and fine products, i.e. for cucumbers, Paris carrots and finger-thick carrots.

Application fields for mechanical peeling machines

Nowadays there are roller peeling machines with high capacities available (dimensions inner space abt. 3 m in length, diameter of screw conveyor up to 1.5 m). With these machines one can achieve considerable throughputs, up to 5 tons of raw goods per big machine. Capacities are, however, lower than those of steam peeling plants.

The following fruit can be excellently peeled in roller peelers: potatoes, carrots, celery roots, beetroot (cooked or uncooked), turnips, kohlrabi and other tubers and root vegetables. Some subtropical and tropical fruits, too, can be peeled mechanically.

The peeled fruit can have a very smooth appearance.

Mechanical peeling technology has to be used, at any rate, in the following cases: in the potato chips industry (GB: crisps) and in the catering section, in industrial potato peeling plants, where potatoes for big canteens, restaurants etc. are peeled. Here, the "cooking ring" would cause a hardening of the peeled potatoes, i.e. a "second skin" which would incur the displeasure of the end user, e.g. the guest in a restaurant.

Here is a true story regarding this matter: the social director of a renowned German chemical enterprise (12.000 servings a day for the personnel) purchased years ago a steam peeling plant for the big canteen of the factory. Due to the "second skin" ("cooking ring"), the guests in the factory-owned restaurant had difficulties in dividing the potatoes on the plates with their forks. The fork would not penetrate the "second skin" as easily as that. It often happened that the potatoes with the gravy slipped from the plate, smudging visitors' clothes. This also happened in the factory-owned restaurant for the high executives of the enterprise and their guests. - The social director was fired. A mechanically working peeling plant was installed by our firm.

Very good peeling results are achieved with the mechanical working Multi-Disc-Peeling Machines (MSS). The latter can both work with blades and with carborundum peeling tools.

Rate of peeling waste in the application of the two peeling methods

The rate of peeling waste in the efficiently constructed and more modern mechanically working peeling plants is not necessarily higher than that of steam peeling plants. By applying the "micro fine-grain peeling", the DORNOW peeling machines can work fairly economically. This method uses a very fine carborundum granulation which takes off only the outer layer of the skin.

On the other hand it is not always expedient to talk about "low waste rates": in the end, the peeled fruit are supposed to reach a certain degree of cleanness! For that, one has often to put up with more waste!

It is not true to say that steam peeling or the brushing machine connected behind would also eliminate eyes and foul spots from steam-peeled tubers and root vegetables!

That steam peeling or the machines connected behind hardly succeed in doing so, is confirmed by the fact that many steam peeling plants are connected with mechanical peeling systems.

Here is an episode: years ago I visited with customers, who were interested in buying our machines, a renowned south German tinning factory. There, a steam peeling plant and a DORNOW roller peeling plant were in operation at the same time. The goods to be peeled were carrots for industry.

The carrots peeled in the steam peeler still showed many black spots. A lot of personnel were busy to remove these spots.

The carrots stemming from the next-door working DORNOW roller peeling plant had been peeled much more accurately, and it did not even take one tenth of the inspection personnel to eliminate the foul spots. Certainly, the roller peeler produced more waste at that time, but the peeled products had the cleanness required in a tinning factory.

That DORNOW roller peeling machines can also work at low waste rates, is demonstrated in the potato chips industry (GB: crisps): Here, the machines peel with waste rates of 6 to 10 per cent. Of course, potatoes peeled that way are not completely clean, but the achieved degree of cleanness will normally do for the chips industry.

On the other hand there are the celery tubers: they have deep tears and splits in their skins which have to be peeled off for the most part. In this case the steam peeler has its difficulties. The DORNOW roller peeling machines, the peeling rollers of which one can make rotate quickly and aggressively, will peel the tubers so fast and accurately that they can be passed on to further processing with a good conscience.

But the DORNOW roller peeling machines can also peel "softly": cooked beetroot (CH: Randen) are peeled neatly and accurately in no time.

Summary

Steam peeling appears to be economically interesting if high peeling throughputs are to be achieved with little floor space being available. Moreover, it is excellently suitable for peeling some difficult and small-sized products.

Mechanical peeling is applied in the low-capacity sector of up to 5 tons of raw material per hour and in those places where it is actually indispensable: in the potato chips industry (GB: crisps) and in the catering sector.

This paper contains non-committal notes. We do not lay claim to completeness. Alterations reserved. 
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Copyright by DORNOW food technology GmbH, D-40549 Düsseldorf

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Dornow food technology GmbH, Willstätterstr. 12, D-40549 Düsseldorf - Germany, USt-Id.-Nr. DE119264470
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Commerzbank AG, Konto-No. 1452333, BLZ 300 400 00, Managing Director Karl-Dietrich Dornow, Amtsgericht Düsseldorf, HRB 22597