Why is cooked tomato paste a doddle to clean off processing equipment compared with milk protein? Why doesn't compressed air, surely the simplest choice for cleaning out food processing lines, never actually work?
When the Food Processing Faraday Partnership was set up three years ago to encourage innovation in the UK food and drink industry, it started off by asking food companies what their technical problems were. And the one big problem everybody came up with was cleaning. Every food manufacturer has to stop production to clean down their processing lines. But how many actually understand how their cleaning system regime works, or whether it is being run as efficiently as possible?
So the Food Processing Faraday Partnership has been trying to discover how food sticks to surfaces and to develop innovative approaches to removing food fouling in process equipment. The results of its work will be presented later this month at its 'Excellence in Food Manufacture 2004' conference being held at Pera in Melton Mowbray.
Some of the results will be surprising. It is easier to clean off baked-on tomato paste than baked-on milk protein because the forces that hold tomato paste together are stronger than those that stick it to the surface of food machinery. So, once you overcome the forces that bind tomato paste to the surfaces of pipes and pumps, you should be able to flush the whole deposit away in one go. However, milk fouling is a different matter. The forces that hold milk protein together are relatively weak, but the final layer that sticks to food equipment surfaces is very difficult to shift.
Also, for years food companies have been trying to blast compressed air through their pipework to clean it, and have failed. Yet by reducing the pressure and stepping up the volume of air used, one company is proving that air is actually a very effective way of cleaning food processing equipment such as pipes. And it can greatly cut down on the amount of cleaning chemicals needed. But you won't hear about that technology at the Faraday conference. It is being developed by a private company founded on the hunch of one man, a former aeronautical engineer. More on that later, though.
"Everybody cleans. And most food companies have automatic clean-in-place (CIP) systems. But whether these systems are optimal, nobody has a clue. Nobody knows how cleaning works," says Professor Peter Fryer, head of chemical engineering at Birmingham University. For the past year he has been finding out how surfaces clean by measuring what force is needed to pull food deposits off a surface.
He has developed a tiny T-shaped probe that scrapes a food deposit horizontally off a stainless steel surface. "You can actually measure what force is required to get things off the surface. So for the first time, you can treat a surface and then measure the change in force that sticks stuff to that surface."
Everybody in the food industry would buy a magic anti-fouling surface or an instant-clean surface if they could, suggests Fryer. "And about every 18 months someone discovers a new one. Some work, but nobody actually has the foggiest idea how. The benefit of our work is that once you can measure the force required to keep something stuck to a surface, or to take it off, you should be able to revisit some of these magic surfaces and say what effect they have."
For his research, Fryer has been using tomato paste, milk proteins, bread, and egg protein. "Milk behaves in a completely different way to starch, for example. This begins to explain why all the previous work on anti-fouling surfaces has been so inconclusive. People have not really understood that it all depends on the sort of deposits you're dealing with. What I will talk about at the Faraday meeting is how you can relate things like surface finish and surface energy to how well your cleaning system is operating."
Fryer foresees his work leading to the development of anti-fouling surfaces for specific food soils. And he plans to build a test rig that will allow companies to work out what their optimal cleaning regime ought to be, without having to stop their processing lines to experiment. "It might end up as the sort of kit your cleaning chemical supplier could install in your factory for a couple of weeks to find out what the best cleaning solution was for your plant."
A row over intellectual property rights among the partners in another Faraday project has rather clouded the success of work into using crushed ice as a way of cleaning out food processing lines. Many food companies adopt the offshore oil industry's practice of 'pigging' to clean their process lines. A soft plug of plastic, rubber or gelatine -- the 'pig' -- is forced through the system to recover valuable unused product between batch changes or prior to CIP.
Professor Joe Quarini in the mechanical engineering department at the University of Bristol has been using crushed ice mixed with a freezing point depressant to pig food process lines. The ice is disposable. There are no mechanical pigs to be captured, removed or cleaned. And crushed ice can refresh those parts other pigs can't reach, such as T-bends and pumps and mixers. Also, both salt and sugar have been successfully used as freezing point depressants.
With his three-year research contract just ended, Quarini is anxious to tell the Faraday meeting about ice pigging's triumphs. It has been tried out at Eden Vale; Golden West (part of RHM and the supplier to McDonald's of sauces and dressings); Geest; and Birds Eye. A spin-off company, CleanIcePig has now been set up by the university to exploit and license the technology, much to the annoyance of the original partners in the project.
Ice pigging can reduce overall CIP times and cut changeover times between batches. But its biggest success is improved product recovery. According to Quarini, with meat slurries such as sausage meat he has been able to get 90-95% product recovery. This has moved one industrial partner to suggest that ice pigging could save it £0.5m a year in product recovery alone.
However, there is one cleaning innovation that's not on the programme for the Faraday meeting. This is air pigging, a technique recently developed by Whirlwind Technologies. According to Paul Baker, marketing director, the Whirlwind system uses relatively low pressure air (or gas) to clean food processing pipes. It claims over 95% product recovery rates for viscous products, rising to over 99% for thin liquids such as soft drinks and whisky.
"Many people have tried to use air to clean pipes, and failed. They have used compressed air and all that happens is that it punches a hole through the product: it never actually clears the product off the pipe walls." So what Keith Roscoe, a former aeronautical engineer and food industry contractor, and founder of Whirlwind Technologies has done, is to develop a two-stage air system. Pressurised air is first used to clear a pathway through the food in the pipe. Then the system switches to relatively low pressure (0.7-1.0 bar), high volume air to sweep the product through the pipe.
"Once there's sufficient pressure to get the product moving, 0.7 bar will move most things," says Baker. "We don't like to refer to it as 'pigging' -- that is old technology. We clear using just air. There is nothing physical in the pipe."
The Whirlwind system has successfully shifted toothpaste, mayonnaise, salsa sauces, pasta sauces, and even solidified chocolate. And one Whirlwind system can be used to clean a number of different lines, simply by opening a valve on the line to be cleared. Since the beginning of the year the company has installed systems at soft drinks company Princes, at Heinz (for clearing baked beans), and at Geest for clearing dips and mayonnaise.
And it has now just launched a CIP version in which fine droplets of chemical cleaning fluids are injected into the air stream. The Whirlwind vortex flow drives the droplets down the pipe clearing and cleaning the pipework at the same time.
Hot air can be used to heat and dry pipes as well. And according to Baker, the system is efficient enough to clear any lingering traces of allergens etc from pipewalls.
Birmingham University, tel: 0121 414 5451
Bristol University, tel: 0117 928 7745
Food Processing Faraday Partnership, tel: 01664 503641
Whirlwind Technologies, tel: 0161 612 8228