Processing of Horticultural Crops (1+2)

Exercise

Practical 14 - Canning of Fruit and Vegetables

Aim: To perform canning of fruit and vegetables.

Theory: Canning refers to a process which involves heating food stuff in hermetically sealed containers for a specific time at specific temperature to eliminate microbial pathogens that endanger public health as well as micro-organisms and enzymes that deteriorate food during storage. Broadly canning is a method of preservation of food for achieving longer shelf-life.
Principle of canning: Destruction of spoilage causing micro-organisms and enzymes within the sealed containers by means of heat.

Machinery/equipments required for canning

1. Can Reformer, Flanger, Double Seamer, Exhaust box, Sterilization tank, Retort, Lye peeling tank and Coding Machine, Refractrometer, gas Bhatti /Boiler.
2. Empty flat cans of A1 tall or A2½ size.
3. Fruits and vegetables suitable for canning
4. Peeling and coring knives
5. Salt or sugar
6. Sodium hydroxide

Canning process: Canning consists of selection of commodity, washing, sorting, grading, peeling, halving, blanching, filling in cans, exhausting, processing, cooling, labeling and storage Figure 14.1.

1. Raw material selection: Select ripe but firm, evenly matured fruits, free from blemishes, insect damage and malformation. Select vegetables when tender except tomatoes.

2. Washing: Wash the fruits/vegetables with running water to remove dust, dirt, debris and any adhering surface micro-flora.

3. Sorting and grading: Sort out any bruised, inferior or damaged fruits either manually or by using sorting belt.

4. Peeling, coring and pitting/halving: Lye peel peaches, apricot, sand pear by placing in boiling 2% sodium hydroxide solution followed by dipping in 1-2% citric acid or 0.5% HCl solution to neutralize lye then wash in running tap water.

• Peel apple manually and slice. Keep in 2% salt solution to avoid browning.
• Cut peeled peaches and apricot into halves and remove the pit/stone. Keep dipped in 2% salt solution to check browning.
• Cut whole pineapple into 5mm thick slices, remove peel and core by using pineapple corers.
• Peel potatoes manually or using abrasive peeler and cut into slices. Keep slices in 2% salt solution to check browning.

5. Blanching: Place mushroom and vegetables in boiling water or in blanching tank for 2-5 minutes followed by dipping in cold water for blanching.

6. Preparation of cans

• Reform the flattened cans using reforming machine.
• Flange in a Flanger.
• Place lid/ end cover on one side of can using double seaming machine.
• Sterilize can in can sterilizer or place in boiling water.

7. Filling into cans

• Place uniform sized peaches/apricot/pear/halves, pineapple slice into lacquered cans to its declared drained weight (not less than 50%). (Generally from one kg of peach fruit, one can of A 2 ½ size is obtained).
• Fill mushrooms and vegetables (peas, okra, potato) in cans of not less than 55% of the total capacity of the can.

8. Syruping: Prepare syrup by boiling sugar and water, followed by straining. Keep concentration of sugar as 35-55%.

• Use 40% sugar syrup containing 0.3% acidity for peach canning. Fill the cans with boiling hot syrup.
• Add the syrup or brine in the can at a temperature of 79-82^OC, leaving 0.32-0.47cm head space.

9. Brining: Prepare hot brine by boiling salt and water (2-10%) along with citric acid (0.3%) and sugar (1%) followed by straining and pour in the can containing vegetable while still hot.

10. Exhausting: Immediately after filling of syrup or brine, place loose lid/ end cover on the can or clinch the can using first operation roll of the double seamer. (The lid/ end cover should be embossed with a coding machine). Place in a hot water tank or in a exhaust box for exhausting. Exhaust the cans till a temperature at the centre of can reaches 79^oC.

11. Double seaming: Immediately after exhausting, seal the cans using double seamer.

12. Heat Processing/sterilization

• Place the sealed cans in boiling water in sterilization tank for 25-30 minutes depending upon the type of fruit being canned.
• Process canned vegetables in autoclave at 10-15 psi pressure (116-121^oC) for 25-30 minutes.

13. Cooling: Cool the heat processed cans immediately in cold running tap to about 35-40^oC to prevent stack burning.
14. Storage

• Stack cans one above other to allow the outer surface to dry to avoid rusting.
• Keep the cans for about a week in the store.
• Label the cans manually or by using labeling machine.
• Store in cool and dry place.

FPO specification for canned fruits and vegetables

Specifications	Canned fruits	Canned vegetables
Drained weight	Not less than 50% Exception: berry fruits 40%	Not less than 55% Exception: canned tomato 50%
Appearance	Free from blemishes, stalks, leaves, etc.	Free from pods, stalks, roots and blemishes etc.
Texture	Free from disintegration and damage from bruises.	Free from disintegration and damage from bruises.
Added colour	No colour except strawberry and cherry	Not permitted, except for peas
Organoleptic quality	Characteristic taste	Characteristic taste
Preservatives	Not permitted	Not permitted
Incubation condition	No positive pressure when incubated at 370C for one week	No positive pressure and sign of bacterial growth when incubated at 37oC and 55oC for one week.