Food for thought: navigating the nation’s appetites

Ready-made meals

The journey begins with a de-nester which feeds trays onto a conveyor belt.

The volumetric filler dispenses a calculated weight of the meal’s bulky ingredients, such as dried pasta or rice.

At the filling station, the pre-mixed sauce is deposited into the tray.

A vibrating conveyor ensures that the ingredients are settled by the time the tray reaches a multi-head weighing station. Load cells deposit precise amounts of expensive ingredients (chicken, meat or seafood) at this stage.

The tray continues to the tray-sealer, where a plastic film is applied. A variable-speed conveyor moves the trays through a microwave tunnel and into a chiller section. When cool, the product is vacuum-sealed.

The tray progresses to the autoclave for sterilisation. This takes 20-40 minutes at temperatures from 110-130°C.

A popular alternative to tins is a resealable, microwaveable pouch, or retort packaging. The pouch is flexible and has a gusset that allows it to stand upright. It is made of heat-resistant laminated plastic and can withstand temperatures of up to 250°C. It uses 5 per cent less packaging than traditional rigid tins and is typically used for rice and pasta meals, sauces and soups.

Canned food

In the case of baked beans, dried haricot beans are soaked in chambers which are heated to 85°C, then the rehydrated beans are washed. Lasers above and below the conveyor detect discoloured beans, which are knocked off the belt by an air jet.

Pre-mixed spices are weighed out by hand in a separate area and added to a container of tomato sauce. Load cells measure the tank levels, and flow meters control the volume of tomato sauce to which the spices are added. A large impeller, powered by an inverter-driven motor mixes the sauce. It is kept warm throughout the filling line by pumps and the temperature is controlled by a programmable logic controller.

Beans are deposited into each can, with sensors checking line control, valve positioning, proximity and deflection throughout the plant. The sauce is squirted at high pressure into each can, a lid is applied and the can is sealed.

The next stop is a steam chamber in the rotary steriliser. The tins are baked for 34 minutes at high temperatures and at high pressure to kill bacteria and maintain the vacuum in the can.

In the packaging area, cameras check that the labels are straight. The final check is a sensor that checks the bottom of the tins to ensure the vacuum ‘headspace’ in the tin is intact.

At the Heinz site at Kitt Green, near Wigan, the distribution centre uses automated vehicles to move the pallets to the vehicle loading area. This site also produces the company’s soups in tins and pouches and baked beans in Snap Pots.

Fish dishes

As soon as possible after the catch is landed, it is sorted into types. Machines remove the scales, skin, head and guts. Fish can be filleted by machine or by hand. Machines can also remove the pinbones or this is done by hand, before final inspection by staff.

The fillets are placed on a roller, which takes them into a deep freezer. Frozen in minutes, the fillets emerge to be weighed, packed and shipped for customers to cook at home.

For fish fingers, the filleted fish is frozen into blocks and taken to a processing plant. A computer-controlled bandsaw cuts them into rectangles. The fingers travel on a wire conveyor to the enrobing station, to pass through a ‘curtain’ of batter before a mix of breadcrumbs, starch and flour is applied.  

After frying for 32-40 seconds, the fish fingers continue on the conveyor to be deep frozen. Conveyors route the frozen fish fingers into groups under suction pumps which lift and place them into boxes. These are placed into cartons and loaded onto pallets for delivery.

For breaded fish steaks, the filleted fish are machine-trimmed to a uniform size and weight before freezing. Conveyors pass them through the enrobing and breadcrumbs stations and then through ovens. The cooked pieces are frozen, packed and weighed before being dispatched for delivery.