Steam power

When it comes to generating steam in a combi-oven, there are two basic systems in use by manufacturers. There's the internal steam-generation boiler, where steam is held until needed and then injected into the oven cavity. Then there's the competing system, called direct injection or spray-on, where water is sprayed on to heated elements within the oven, generating instant steam.

It used to be that manufacturers in northern Europe - the UK, France and Germany - opted for the steam boiler, while manufacturers in southern Europe - Spain and Italy - preferred the spray-on system. Each had convincing arguments as to why their steam-generation system was best, and why the opposing option was fundamentally flawed. It was no surprise, then, that many chefs were left slightly confused.

The north-south divide began to break down about five years ago. While manufacturers such as Rational in Germany and Falcon in the UK were adamant that steam generators were the only sensible long-term answer for the combi-oven, global leaders such as Electrolux and Lainox saw more sense in producing combi-ovens using both systems, to satisfy a wider market.

It didn't really matter where an equipment company was based, either. Its head office location could well bear no relation to where the equipment was manufactured, so buying a combi-oven with a British name did not mean a chef was buying into a chilly-climate, north-European steam-boiler generation system. The oven could well have been made in the foothills of the Dolomites in Italy.

This brings us into the world of badging, where the logo on the front of the machine might name one manufacturer, but the combi-oven is actually made by another. Makers of catering equipment, from the biggest to the smallest, are going down this path.

There is an urban myth that there are about 68 combi-oven suppliers proudly showing their logos on their ovens, but no more than 12 companies that actually make them. Almost all are based in Europe, as combi-oven technology is not something US or Asian equipment manufacturers have got to grips with.

How to buy

Sterling Foodservice Design is one of the UK's leading catering kitchen designers, specifying many combi-ovens each year. Here is its guide to choosing the right type and size of combi-oven for you.

• How big?

  Six-grid size: up to 120 covers

  10-grid size: 150-180 covers

  20-grid size: up to 250 covers.

• Determine the size and configuration of ovens according to menu and schedule, by considering whether one 20-grid oven is better than two 10-grids, or two six-grids, or a 10-grid plus six-grid stackable.
• Determine what is to be cooked or regenerated when deciding on which manufacturer's oven is appropriate - some have a larger internal cavity, a few will accept traditional roasting tins, and others may take only gastronorm pans.
• Does the oven have a cleaning programme, and is this important to you?
• If you are intending plated service, check plate capacities. One 20-grid oven cavity may accept up to 76 plates for a seven-minute regeneration time, as opposed to only 60 plates in another. This can have a major impact on banqueting.
• Ensure that the manufacturer or supplier provides a guaranteed call-out response.
• Ensure adequate ventilation. New Heating and Ventilating Contractors' Association guidelines state that there must be a 600mm overhang above combination ovens and an adequate flow rate of extracted air.
• Check fire safety needs with your fire officer.
• Avoid positioning the combi-oven next to grease-producing appliances such as fryers and chargrills. Grease-laden steam can penetrate access panels and deposit grease on service chambers, damaging working and electrical parts.
• Consider fitting a drainage channel in the floor in front of the oven to deal with spillages and for health and safety reasons.
• Be certain that a combi-oven is really what you need. If the main purpose is for bakery work with bread and desserts, then the small amount of steam needed can be provided by a convection oven with a humidifying facility.

Contacts

The following manufacturers and distributors contributed to the debate on steam-generation systems for combi-ovens:
Angelo Po 01332 638030
Electrolux 0121-220 2800
Enodis 020 8561 0433
Falcon 01324 554221
Hobart 07002 101101
Lainox 01226 350450
Lincat 01522 875555
Olympic Catering Equipment 01245 265355
Rational 01582 480388
Sterling Foodservice Design 0121-445 0900

Point/counterpoint

So what are the pros and cons of the two steam-generation systems? Manufacturers and distributors were asked for their arguments. Some of the manufacturers were steam-boiler only, some spray-on only. Others produce and sell both in the UK; some produce both, but do not sell spray-on steam systems in the UK. Here are the main points put forward by both sides.

The case for spray-on steam

• The overall costs of a spray-on steam system are less than with steam boilers.
• Spray-on generates steam quicker, as steam boilers need time to heat up.
• Spray-on uses and heats only the water it needs, thus saving on utility costs.
• Any limescale problems can be spotted early, and the cost of dealing with them is much less than with a steam boiler.
• The steam boiler feature can regularly go wrong on a combi-oven, making maintenance essential.

The case against spray-on steam

• The elements on to which cold water is sprayed can see heavy limescale build-up if no water filtration system is fitted, affecting efficiency. However, some manufacturers believe it is necessary to fit a water-filtration system to all combi-ovens, irrespective of the prevailing water hardness, since water hardness changes and water is moved around the country. They believe the absence of a water-filtration system can contribute to corrosion and welding problems on both systems.
• If no filtration system is fitted to the spray-on steam combi, then any particles in the water are sprayed on to the food and there can be a build-up of limescale in the cooking cavity.
• Cold water sprayed on to hot elements cools them, forcing the oven to regain the correct temperature and, therefore, causing longer cooking times and higher energy costs.
• The amount of steam introduced into the cooking cabinet cannot be controlled with a spray-on system as water, not steam, is fed into the cabinet. Steam boilers offer very tight control, essential for delicate work such as pastry.
• The stresses to the metal caused by continually spraying cold water on to hot steel elements leads to high maintenance costs. Three to four years is a common life span for a spray-on element.