FOOD TECHNOLOGY-1

Module 5. Jam, jelly, marmalade, and glazed and crystallized fruits

Lesson 19
FRUIT PRESERVES

19.1 Introduction

Fruits are seasonal in nature. Further, it has got limited shelf life. Sugar has got the ability to increase the shelf life of fruit products through its osmotic pressure action on microorganisms. Preparation of fruit preserves is one novel method of preserving the seasonal fruit for use in non-season or to make available the ‘fruit of choice’ for the consumers to enjoy throughout the year.

19.2 Preserves

They are whole fruits or large pieces of fruit in thick sugar syrup, often slightly jellied. Preserves are made from practically all fruits including peaches, pears, plums, aonla, strawberries, grapes, muscadines, quinces and tomatoes.

The fruit for preserving should be in a firm-ripe rather than a soft-ripe stage. By using up to 25.0% of firm-ripe fruit, the tartness is increased and less pectin is required in the formula. The fruit should be uniform in size and uniform pieces so as to cook evenly.

The examples of Preserves include Fig preserve, Watermelon rind preserve, etc.

19.3 Preliminary Processing

The fruit should be washed thoroughly. If the fruit had been sprayed with insecticide to check blight, it should be washed with dilute HCl, especially is the peel is not removed from the fruit for preparation of the preserve.

The preliminary treatment varies with the variety of fruit taken. For instance, apples and pears are just peeled and pricked if they are to be kept whole, otherwise they are peeled, halved or quartered, cored and punctured. Mangoes are peeled, sliced and pricked. Peaches are destoned and lye peeled. Apricots, cherries are only pitted and destined. Oranges, lemons, grape fruits and citrus fruits are halved and the pulpy portions removed from the cut fruit. Pumpkins are sliced, peeled, pricked and placed in dilute lime water for few hours to harden the texture. Strawberries and Raspberries are used as such, without any preliminary treatment.

The fruit is first cooked slightly in water to make it soft enough to absorb sugar. Cooking of the fruit in syrup is rather a difficult process, because the syrup is to be maintained at a proper degree of consistency so that it can permeate the entire body of the fruit, without causing it either to shrink or to toughen. The fruit should be boiled initially in water before transferring it to the syrup or cooked first in a dilute syrup with low sugar concentration. Highly juicy fruits may, however, be placed directly in a thick syrup at the very outset, because the excess of juice present in the fruit would serve to dilute the syrup.

19.4 Cooking in Syrup

There are three ways of cooking the fruit in a syrup. These are: (i) Open Kettle one period process, (ii) Open kettle slow process and (iii) vacuum cooking process.

19.4.1 Open kettle one period process

The concentration of the starting sugar syrup for cooking the fruit should be low. Boiling should be continued with gentle heating until the syrup becomes sufficiently thick. Rapid boiling will make the fruit tough, especially when heating is done in large shallow pans with a small quantity of syrup. Soft fruits such as strawberries and raspberries require little boiling for softening, unlike hard fruits like apple, pear, peach, etc. which require prolonged heating. The final concentration of sugar syrup should not be less than 68°Brix, which corresponds to a boiling point of 106°C at sea level.

19.4.2 Open kettle slow process

The fruit is first cooked in water to make it tender. Sugar equal to half the weight of fruit is added to the boiled fruit in alternate layers in a vessel and the mass is allowed to stand for 24 h. During this period, the fruit gives out excess water, and the sugar goes into solution resulting in a syrup of ~ 38°Brix. More sugar is added to raise the strength of the syrup to about 60°Brix. A small quantity of citric or tartatic acid (62-125 g per 100 kg of sugar initially taken) is added to invert a portion of the cane sugar. The whole mass is then boiled for 4-5 min and kept for 24 h. On the 3rd day, the strength of syrup is raised to ~ 68°Brix by adding sugar and the mass is boiled again for 4-5 min. The fruit is then left in the syrup for 3-4 days. Finally, the strength of the syrup is raised to 70°Brix and the preserve, in finished condition, is then packed in containers.

19.4.3 Vacuum cooking

Preserves made by cooking under vacuum retain the flavor and colour better than those made in open kettles. In vacuum cooking process, the fruit is initially softened by boiling and then placed in the syrup, which should be about 30-35°Brix. The fruit syrup blend is then transferred to a vacuum pan and concentrated under reduced pressure to ~ 70°Brix. Hard fruits like apples and pears require slow boiling to facilitate penetration of sugar, while soft fruits can be boiled briskly.

19.5 Cooling and Packing

If the preserve is to be stored in bulk, it should be cooled quickly after the first boiling to avoid any discolouration of the product. The fruit is drained from the syrup and filled into dry containers. Freshly prepared boiling syrup of 68°Brix is then poured into the containers such as in A 2.5 size cans, which are exhausted for 8-10 min at about 100°C in steam, and then hermetically closed.

If the preserve is packed scalding hot in dry cans, subsequent sterilization of the cans may be omitted. A 2.5 size (can hold 28.5 fluid ounce i.e. 843.6ml) can may be preferably sterilized for about 25 min at 100°C and cooled immediately thereafter.

19.6 Typical Examples

The examples of sugar preserves include Aonla preserve, Apple preserve, Bael preserve, Carrot preserve, Cherry preserve, etc. The process of manufacturing two such preserve is discussed herein.

19.6.1 Aonla preserve

Aonla preserve is a highly valued product in India as it is associated with valuable therapeutic properties.

Select large fruit (Benarasi variety preferred) for making the preserve. Wash the fruit in water. Prick them with a needle of bamboo/wood/stainless steel. Place the pricked fruits in 2.0% common salt solution. Raise the strength of the salt solution progressively by 2.0% on subsequent days, until the final concentration reaches about 8.0%. Wash the fruit in water and place them in freshly prepared 8.0% brine for about a week. This treatment removes most of the astringency in the fruit. Wash the fruit again. Blanch the fruit in 2.0% alum solution until they become sufficiently soft, taking care to see that the segments do not break or crack in the process. They are then passed through several stages of syrup treatment just as for apples. The final product should be packed in lacquered cans.

19.6.2 Apple preserve

Specifically two varieties namely the Sweet and the Sour ones are preferred for preparing Apple preserve and Apple candy.

Peel the apples thinly, but do not remove the stem and core. Prick the peeled fruit with a stainless steel needle or fork. Place the sweet variety of apple in 2-3% common salt solution and the sour variety in plain water to prevent browning and disintegration of the fruit during subsequent blanching. Transfer them next to dilute lime water (2 parts of lime water and 1 part of water) and leave them for 24 h. Prepare 2-3% alum solution and bring it to boil in a pan. Now transfer the apples to this boiling solution. Add a small quantity of sodium bisulphate to whiten the colour of the apple. Continue boiling until the fruit become soft. Take out the fruit and place them in cold water, discarding the blanching solution. Prepare fresh alum solution separately for each batch. The cooled apples are now ready for the syrup treatment.

Take sugar equal to half the weight of prepared apples. Usually 74-76 kg of sugar is required for every 100 kg of the whole apple, prior to peeling. Place the sugar and apples in alternate layers in a vessel and leave the mass undisturbed for 24 h. During this period, the fruit will give out sufficient water to dissolve the sugar. Ordinarily, the resulting syrup will be of 36-38°Brix. Next, boil the mass for a few minutes and raise the strength of the syrup to ~ 60°Brix by adding more sugar. Next, add a small quantity of citric or tartaric acid, or invert sugar or corn syrup to the extent of 25% by weight. After boiling for a few minutes, let the apples remain in the syrup for another 24 h. On the 3rd day, raise the strength of the syrup to 70°Brix and let the product stand for a week. Now, the preserve is ready for packing in jars or cans.

If the preserve is to be candied, the Brix of the syrup should be raised to 75°Brix and again allowed to stand for another week, before it is ready for candying.