NO790428L - PROCEDURE FOR PEELING FRUIT AND VEGETABLES - Google Patents

Description

Procedure for peeling fruit and vegetables.

The present invention relates to a method for peeling fruit and vegetables by heating with aqueous alkali.

In the known methods for peeling fruit and vegetables by heating with aqueous alkali, sodium hydroxide or potassium hydroxide has been used as alkali, as it has been considered necessary to use the strongest possible alkali to remove the skins. However, the method has significant disadvantages, which are due to the fact that it requires too long a heating period to provide a suitable degree of peeling, which is why it is expensive in terms of heat energy and is only suitable for peeling such fruits and vegetables that are still desired to be cooked, but are less suitable for peeling fruit and vegetables that do not have to be cooked or softened, e.g. because after peeling they must be subjected to mechanical treatments, which can hardly be done with a soft material, e.g. chopping onions and cutting potatoes into chips.

It is also known to peel fruits and vegetables by heating with aqueous solutions of ammonium salts, which are significantly weaker alkalis than sodium and potassium hydroxide. However, this method is very inappropriate or expensive, because in practice it can only be carried out in pressure vessels, as ammonia is otherwise avoided during the heating.

According to the invention, it has now been shown that the disadvantages of the known methods for peeling fruit and vegetables can be avoided by fully or partially using potassium carbonate and/or potassium urn phosphate as alkali. You thereby achieve faster peeling than when using sodium or potassium hydroxide, and thereby a better utilization of the device's capacity, and you can work with open containers.

Peeling of fruit and vegetables in the present context is understood to mean the removal of the outermost layer of cells from the relevant plant part, whether this outermost layer has the character of an actual skin that is clearly distinct from the rest of the fruit or vegetable, such as potatoes and apples, or if the outermost layer is in principle of the same nature as the rest of the plant part, such as e.g. on onions, where there is no sharp transition between dry and juicy skins.

Peeling of fruit and vegetables is not normally carried out to a peeling degree of 100%, i.e. the peel is removed from 100% of the surface, because this would take too long and thereby change the interior of the fruit or vegetable. In general, you can count on a ■peeling degree of 80 to 100? is satisfactory, depending on the nature of the relevant plant part.

The invention shall be illustrated in more detail by the following examples, all of which are carried out by immersing the fruits or vegetables in question in the heated aqueous solution of alkali and keeping it there for a period of time, until a discretionary, acceptable degree of peeling is achieved. They are then taken up by the peeling liquid and rinsed with water, and the peeled area is measured as a percentage.

Example 1. Potatoes.

Bintje potatoes were used, and the peeling liquid was kept at 90°C. The chemicals used were 9g K^ CO^ per liter and 56g KOH per litres. A peeling degree of 85% was achieved in 6 minutes. If potassium hydroxide alone is used in a concentration which gives the same concentration of potassium ions, namely 63g KOH per litres, only a peeling degree of 65% was achieved on

6 minutes.

In comparison, a peeling time of 8 minutes was required

to achieve the same peeling percentage when the chemicals used were the corresponding sodium compounds in a concentration which gives the same normality of the peeling solution, namely 7g Na2C0-

per liter and ^0g NaOH per litres.

Example 2.

That it is not only the potassium ion, as opposed to the sodium ion, that is decisive for the result, is seen by a further comparison experiment, in which Bintje potatoes of a different origin than those in example 1 were used, and where the peeling liquid was again kept at 90 °C. When the chemicals used were 69g K^ COj and 42g KOH per litres, a peeling degree of 75% was achieved in 6 minutes, while a peeling degree of 55% was only achieved when the chemicals used were 7^.5g KC1 per liter and 42g KOH per litres.

Example 3- Potatoes.

Bintje potatoes were used, and the peeling liquid was kept at 90°C. ' The chemicals used were 4Og K-^PO^and 46g KOH per litres. A peeling degree of 90% was then achieved in 6 minutes.

In comparison, a peeling time•of 8 minutes was required to achieve the same degree of peeling when the chemicals used were the corresponding sodium compounds in a concentration which gives the same normality of the peeling solution, namely 31g Na^PO^ per liter and 33g NaOH per litres.

Example 4. Apples.

Apples of the Spartan variety were used, and the peeling liquid was kept at 70°C. The chemicals used were 35g K-jCO^pr.

liter and 21g KOH per litres. A peeling degree of 85% was then achieved within 6 minutes.

When the chemicals used were the corresponding sodium compounds in a concentration which gives the same normality of the peeling solution, namely 27g Na^CO^ and 15g NaOH per litres, 10 minutes were required to achieve a peeling degree of 80%.

Example 5 - Apples.

Apples of the Spartan variety were used, and the peeling liquid was kept at 70°C. The chemicals used were 35g K^PO^ and 18g KOH per litres. A peeling degree of 90% was then achieved within 6 minutes.

In comparison, a peeling time of 10 minutes was required

to achieve 85% peeling, when the corresponding sodium compounds were used in a concentration which gives the same normality of the peeling solution, namely 27g Na^po^ and 13g NaOH per litres. Example 6. Apples.

Apples of the Springrove variety were used, and the peeling liquid

was maintained at 70°C. When the chemicals used were'69g K2C0^

and 28g KOH per litres, a peeling degree of

100$ within 6 minutes. However, when the chemicals were 74.5g KC1 and 28g KOH, no peeling at all could be achieved

in 6 minutes.

Example 7. Onions.

Onions of the Zittauer variety were used, and the peeling liquid was kept at 80°C. When the chemicals used were 9g ^CO-^and 14g.K0H per liter, a peeling degree of 85$ was achieved within 6 minutes.

To achieve the same degree of peeling, a processing time of

10 minutes, when the chemicals used were the corresponding sodium compounds in a concentration which gives the same normality of the peeling liquid, namely 7g Na2C0^ and 10g NaOH per litre.

Example 8. Onions.

Onions of the Zittauer variety were used, and the peeling liquid was kept at 80°C. When the chemical used was 35g K^PO^y, a peeling degree of 85% was achieved within 6 minutes. Application of 27g Na-^PO^pr. liter only gave a peeling rate of 70$ in 10 minutes.

Example 9- Onions.

Onions of the Stuttgarter variety were used, and the peeling liquid

was maintained at 70°C. When the chemical used was 71g KjPO^pr. liters (which gives a normality of 1), a peel rate of 90$ was achieved in 10 minutes. 8^ KOH per litre, which gives the same normality of the peeling solution, results within 10 minutes in a degree of peeling of 97$, and 60g of NaOH. per litres, which also gives the same normality of the peeling solution}results within 10 minutes in an unsatisfactory degree of peeling of 30$.

Claims (1)

'Procedure for peeling fruit and vegetables by heating aqueous alkali, characterized by ■ that potassium carbonate and/or potassium phosphate are used as alkali in whole or in part.