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"State of the art" steam peeling or thermal conditioning.

"State of the Art" Steam Peeling or Thermal Conditioning

Machines commonly known in the food processing industry as'steam peelers' are not, in fact, what their name suggests. If, in our industry's early years, the steam peeling processes had been more closely analyzed we might very well have referred to them as'product conditioners'. or'thermal conditioners' instead.

The Early Years

The very first attempts at peeling root crops using thermal processes homed in on the basic concept of all thermal peeling systems. The idea was to weaken the structure supporting the skin and that which was immediately below the skin so that, when it disintegrated, it also released the skin. The first processes therefore used scalding hot water. The inventors had already determined that the best way to weaken good potato flesh was to cook it. Results were laborious and unpredictable. Very quickly thereafter much more meaningful results were obtained by feeding potatoes into a continuous screw with a steam-tight valve at both the infeed and discharge ends. This product was developed by the Food Machinery Corp in America (or more accurately its predecessor IMC) where the cooking medium was low pressure steam. The root crops were cooked for a considerable depth below the skin. After discharge the products were put into enormous bar reels with huge quantities of water being sprayed on them. Product to product contact and pro-duct to bar reel contact destroys the cooked vegetable releasing the skin.

In these early conventional steam units the raw vegetables were effectively semi cooked and produced substantial heat rings. Considerable peel loss was also a result. This was mainly because of the length of time the product had to remain in the steam environment.

Heat rings have never been a problem if the products went on to further the processing, ie, manufacture of potato crisps, French fries, in canning or in freezing. Generally speaking, the further processes involve blanching techniques which continue the cooking operation to a large degree. Major problems occurred however where the products had to be preserved even for short periods. It was also found that the heat ring interface tended to harden when in contact with water and/or sodium metabisulphide. This hardened texture of that part of the potato manifested itself into hard particulate matter when the product was subsequently processed.

A solution was found when the H and H Group company, Komen and Kuin developed a new generation of thermal conditioners. Their engineers carried out much more detailed evaluation in conjunction with technicians from the IBVL Institute at Wageningen in Holland. It was determined that only a minimum amount of thermal processing was needed to allow the skin removal to take place. Many experiments were carried out, with one major conclusion being determined

If high pressure super-heated steam was used as the heating medium, and for very short periods of time, then the molecules of water lying immediately underneath the skin were heated to temperatures well above boiling point but with the liquid remaining as a liquid under high pressure conditions. It was indeed the concept of pressure cooking. Instantaneous release of the pressure meant that these high temperature molecules of water evaporated to steam instantaneously. As steam takes up many times the volume of water there was indeed an implosion from within the product. This loosened the skin and at the same time caused minimum heat rings.

Komen and Kuin had recognised, however, that the peeling machine was indeed a thermal conditioner. They went on, therefore, to invent the centrifugal dry deskinner. This machine is a composite and essential part of a thermal peeling system. The concept is that product is centrifugally spun to the outside of a rotating drum, whilst being mechanically and positively conveyed through it. Product to product and drum to drum contact are more relevant to the final process. The end result is that skin is'abraded' from the potato as is the majority of the already minute heat ring. It is often the case that, when product is examined, heat rings are not noticed.

The new generation machines achieve a more efficient cycle by incorporating the latest advances in thermal conditioning technology. They have a well engineered and enlarged steam inlet/outlet system complimented by a specially designed steam distribution unit. This is fitted within the vessel. Many steam peelers had steam injected directly into the vessel. The K and K system has a distributor mounted in from the side. Steam distribution takes place in a very even way whilst the product is gently rotated as the drum turns. It has been found that steam distribution is of immense importance in these thermal conditioners. Static vessels, with or without agitators, do not produce as even a conditioning result as rotating vessels.

A further development of the system has recognised that condensate removal can be an advantage when handling some root crops, such as carrots, swedes, turnips, etc, but a definable disadvantage when handling starch based products such as potatoes. The new thermal conditioner therefore can be supplied with or without condensate removal. When supplied with the system included, it is capable of being isolated according to the product being processed. The Flo-Mech/ Komen and Kuin thermal conditioning systems are often installed as part of existing lines. The system comprises the stages of bulk feeding, weighing, thermal conditioning, centrifugal dry deskinning followed by polishing, if that is a feature desired by the customer.

PHOTO : One of the new generation thermal conditioners
COPYRIGHT 1989 Food Trade Press Ltd.
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Copyright 1989 Gale, Cengage Learning. All rights reserved.

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Author:Barratt, Richard
Publication:Food Trade Review
Date:Sep 1, 1989
Previous Article:Operational characteristics of a new steam system and its potential for energy saving.
Next Article:Maize products - their uses in the food industry.

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