By Michelle Knott

- Last updated on GMT

Related tags: Food, Heat exchanger

Get food industry engineers reminiscing and they'll tell you about a golden age when yogurt was yogurt and there was only one type of cottage cheese. They'd start production in the morning and stop at the end of the day for a good old-fashioned clean down. These days the proliferation of new product variants is unstoppable, whether it's exotic new flavours or varying degrees of fat-free, organic, allergy-aware or value versus luxury lines.

For typical food factories this proliferation of wild and wonderful varieties is piling on the pressure to manage more batches and have shorter production runs, leading to more frequent changeovers.

Pipework, heat exchangers and other equipment needs to be cleared of one product before it can handle the next one, and that can be a time-consuming business.

It's also expensive, since any product washed through at the start or end of a run is wasted, on top of the cost of water, chemicals and energy.

Luckily, opportunities to improve product recovery and speed up changeovers have not gone unnoticed and solutions are emerging. Some of these aim to improve product recovery and speed up changeovers across a range of equipment, while others aim to make the processing equipment itself more changeover-friendly.

For example, recent months have seen at least six food companies trialling a new type of depositor, which aims to improve on the traditional rotary valve and piston-based equipment that has dominated the market for 30 years. The system was developed by the Food Processing Faraday and Sapcote Engineering is now on board to deploy and tweak the prototype for trials.

Depositor developments

Depositors conventionally comprise a hopper with a rotary valve and piston mechanism underneath to dispense repeated portions of product, whether it's filling jars of mayonnaise or adding pizza topping.

"The trouble is that the product passes directly through the guts of the machine,"​ says David Walklate, innovation consultant with the Food Processing Faraday. "The whole thing needs to be stripped down by the hygiene team for each changeover."

The new hygienic depositor instead uses a milking action to portion out the product through a flexible tube. With this set-up it's only the tube and the hopper that come into contact with the product, making it easier to clean at the end of run as the entire machine doesn't have to be stripped down. The tube and hopper can instead be swapped for clean versions almost instantly.

"The point was for it to do the same job as a rotary valve and piston depositor but meet the need for instant changeover," ​says Walklate. "But we found there was an unexpected bonus when it's handling particulates. If there's a lump it tends to slip to one side or the other as the tube is squeezed and so remains intact."

There are other potential savings too, according to Walklate: "Whenever you finish a run that uses multiple depositors, there's almost always some of one ingredient or another left at the end. It tends to get wasted when the depositor gets washed down. With our system you could take the hopper and tube, fit a lid, put it in the cold store and keep it overnight to use again tomorrow, shelf-life permitting."

The food industry is notoriously conservative when it comes to trying new equipment, but the prototype system has already been doing the rounds of commercial trials, with potential users being offered favourable terms if they choose to buy one. "We're offering a full performance guarantee," ​says Walklate. "If it doesn't do what you want it to do then you don't pay for it you can't say fairer than that."

Of course, there's a lot more to most production lines than depositors. Pipes, heat exchangers, mixers and so on all present a challenge during changeovers.

Some industries, such as petrochemicals, have long used solid plugs called pigs to clean their pipework, but traditional pigging has historically failed to fly very high in the food industry. "Rigid pigging systems require perfect pipes," ​says Jonathan Harper, md of Martec Conservation, which specialises in product recovery solutions.

Unfortunately, we don't live in a perfect world. Pipes get dented, fitters bend them into weird elliptical shapes as they force them to marry up, sharp bends wind their way around other equipment and flexible hoses flex. Any or all of these everyday obstacles might mean that food manufacturers end up with a system that doesn't live up to its promises. "When we first started looking into opportunities in the food industry we were thrown offsite in a couple of places because companies had bought conventional pigging systems that weren't up to the job," ​says Harper.

Martec's innovative Marplug device has a rubbery central body surrounded by a series of flexible blades that slip along the pipe walls a bit like a squeegee. This flexibility allows the Marplug to negotiate a wider range of dents, lips and bends without getting stuck, as Martec is happy to demonstrate in its purpose-built obstacle course.

The right skills in place

But Harper stresses that it takes engineering know-how as much as nifty equipment to make the most of a product recovery system. "We first take time to understand how the customer makes their products. In a new facility we'll help them design a system that minimises the number of pipes and valves," ​says Harper. "When we're retrofitting we'll carry out tests to validate that the existing pipework is fit for purpose and that the product is successfully removed as predicted, so that the expected improvements in yield will be realised."

Martec admits that its approach is not appropriate in every application. In a small-bore pipe carrying thin, low-value product, for example, compressed air purging would probably be the most cost-effective solution. "One dairy estimated that they could save £300,000 of milk by clearing their pipes using a Martec system, but we persuaded them that a much cheaper solution was to install a turbidity meter so they could monitor the transition between milk and water when they cleaned the system. We always try and recommend the best solution," ​says Harper.

But where it is the right approach, the potential benefits of flexible Marplug solutions are substantial. Martec says it can shave 15 minutes off a 45-minute cleaning-in-place (CIP) cycle. "If you're doing four batches a day it means you might have time do five, increasing the throughput of the plant," ​says Harper.

The company has also launched its own range of heat exchangers to boost product recovery. Where a conventional scraped heat exchanger might end up with 15% of a 300500 litre batch of product to be cleaned away at the end of a run, a Marplug can recover almost all of it from a Martec heat exchanger.

Ice pigging

Food industry trials are currently underway on another solution that could prove to be even more flexible for product recovery: ice pigging. The idea emerged from a research project at the University of Bristol. As the name suggests, it relies on pushing a plug of ice slurry through pipework and other equipment. That includes virtually anything, including T-junctions, heat exchangers, mixers and pumps.

Ice pigging has already taken off commercially as a technique for cleaning potable water lines in the utility industry, and the Department for Environment, Food and Rural Affairs (DEFRA) has now contracted with nine partners to trial the system in food applications. These include major players such as Premier Foods, Greencore and General Mills.

An ice pig is an abrasive mass of crushed ice that cleans pipes as it's pumped through. It's a deceptively simple idea, but it calls for specialised ice systems that can freeze water into a slurry and stir it as it forms, keeping the ice crystals small. A freezing-point depressant such as salt or sugar stops the crystals freezing together into a solid plug. The pig must be delivered correctly to insert it into the pipework without the ice and water separating.

Like other product recovery solutions, ice pigging can reduce overall CIP times and cut the changeover times between batches. The University has tested the system with meat slurries such as sausage meat and achieved 9095% product recovery. "It's difficult to quantify savings because it depends on the set-up and the product being recovered, but the potential is enormous,"​ says Joe Quarini, the process engineering professor who has championed ice pigging at the University.

The chemically benign ice is ideal for product separation between similar products such as reduced fat and standard mayonnaise, or strawberry and raspberry yogurts, for instance. And because it's disposable, it doesn't create the hygiene issues that can sometimes be associated with solid pigging systems.

The DEFRA-sponsored trials started in January this year and the contract will run until December 2012.

Key contact

 Food Processing Faraday 01664 420066
 Martec Conservation 01246 860855
 University of Bristol 0117 928 9000

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