CESA guide: warewashing

12 February 2010
CESA guide: warewashing

They're the unglamorous workhorses of the kitchen and are very demanding in energy terms - but surely no sensible chef would want to be without their warewasher.

The poor old dishwasher is at the bottom of the catering equipment pile - it's not sexy, no one wants to look after it, it tends to belch out clouds of steam and it is a major consumer, not only of energy but of water and chemicals, too. Yet every caterer relies heavily on their dishwasher and every publican on their glasswasher - when things go wrong, it's panic stations.

Choosing the right warewasher is a balancing act - price will always be a critical factor, but these days running costs should weigh at least as heavily in the buying decision. A machine that's built to use less energy and last longer will cost more initially, but should give a better return on investment over the years. In addition, it will be more reliable.

Alongside glasswashers and dishwashers, there are specialist utensil-, cutlery- or pot-washers.

Broadly speaking, warewashers come in four varieties:

â- Door-type, pass-through, hood or stationary rack machines are one of the most common types of warewashers because of their size and versatility. Usually found in sites with fewer than 150 seats, these units can wash up to 62 racks of soiled dishes per hour. Pass-through machines are built to hold one or two standard size dish racks.

â- Rack conveyor-type warewashers use a conveyor to move racks of soiled dishes from a table on one side, through the machine and on to a table at the discharge end of the machine. These machines are designed for larger operations and are capable of washing 125 to 360 racks of soiled dishes per hour.

â- Flight-type machines, also called rackless machines or belt conveyors, deliver warewashing on the largest scale. Measuring up to 18 meters long and capable of washing as many as 24,000 dishes per hour, they are the primary choice for large institutions.


A relatively new technology is reduced temperature washing. Used mainly in glasswashers, it washes with water at just 40e_SDgrC and has two key benefits: cooler glasses out of the machine and lower running costs. Cooler glasses can be reused straight from the machine, a major benefit in busy pubs and bars. The reduced temperature cuts energy consumption significantly, although specialist detergents and rinse aids may be required.


Many manufacturers have focused on developing warewashers that save water - because a machine that uses less water will also use less energy (since it won't need to heat up as much water) and fewer chemicals. Sophisticated filtration systems that filter dirt out of the water so that it lasts for more washing cycles can have a huge impact on water consumption.

Heat exchangers that recycle the heat from steam and waste water have been around for a while in big machines, but some pass-throughs and even undercounter units now have them, too. These features can make a big dent in running costs, saving hundreds or even thousands of pounds a year.


Q We're going to need a variety of dishwashers for our site, a new-build leisure and conference facility, which is spread over a wide area and includes fine-dining restaurants, fast-food outlets and a large conference venue. Is there a way to work out what size of machine each facility will need? (Manager, new-build leisure and conference facility)

A Manufacturers will give the maximum performance of a machine and the industry standard is to assume an operator efficiency of 70%. In other words, if a machine is theoretically capable of washing 100 racks per hour, assume it will do 70.

The calculation below works for machines using standard racks holding about 20 dinner plates.

First establish how many dishes and glasses each customer is likely to use (in a limited menu café the figure might be as low as five pieces; in a fine-dining restaurant it might be 20). Then work out how many people per hour the site will serve at peak times. Work out the number of dirty pieces they will generate per hour, then factor in the 70% operator efficiency standard to work out the machine capacity you will need.

Customers/h x pieces per customer = pieces/h.
Pieces/h Á· 70 x 100 = capacity required.

For example: a restaurant serving 120 customers per hour, each using 13 dishes or glasses, will generate 1,560 pieces per hour. 70% operator efficiency means the machine will need a theoretical capacity of 2,229 pieces, or 112 racks, per hour.

Q The new dishwasher in our 50-bed care home is not giving very good cleaning results, plus it seems to be producing a lot of foam. What's wrong? (Owner, 50-bed care home)

A Water pressure is extremely important to the cleaning process. Under most conditions, the machine's water pump can supply enough pressure. However, protein soils in the wash water can combine with detergent chemicals and cause foaming. Foam strangles the water pump, reducing its efficiency. Not only does this impair washing results, but also the foam is quite often carried over into the rinse stage, further compromising the results. Try using a detergent with a de-foamer and make sure staff scrape the plates properly.

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