Microwave moves
Not so long ago, a microwave oven was just a small cabinet that belted microwaves into food to heat it up. There are still a lot of microwave ovens that perform only this rudimentary function, but some are getting smarter, using other heat forms, growing bigger and blurring in their function with full-size ovens.
Microwave ovens work by heating anything with moisture content, which is why they're suited to the regeneration of frozen food, which has a high water content. However, the microwaves have difficulty penetrating beyond 35mm and rely on heat conduction to spread the heat throughout the food. This is something of a problem with simple microwave ovens and can result in the outside of the product being tongue-burning hot while still chilled deep inside. This is not only a food safety issue but also makes it apparent to the customer that the food is frozen rather than freshly prepared on site.
One of the most popular pub menu items supplied frozen is individual lasagne, which also highlights the limitations of a basic microwave oven. Lasagne is a mixture of texture densities, from the loose béchamel sauce to the firm pasta. It's also a deep product: too much power and it's dried up on the outside, too little and, while the sauce and outside are fine, there may be cool spots inside.
Lee Tynan, development chef for frozen food supplier Brakes, says the lasagne is indicative of how different foods need different reheating methods. While most foods are microwaved by caterers from frozen, Tynan says many frozen foods reheat better after being defrosted, lasagne being one of them. Rather than being bombarded on maximum power, lasagne needs a gentler period of half-power, followed by a finish on full power.
The lasagne problem isn't made easier by the fact that with many microwave ovens the magnetrons that generate the heat are above the food. Effective stirring of the microwave energy should ensure a good distribution of heat, though manufacturer Sanyo has models which have magnetrons both in the roof and the base of the oven cavity, which it claims greatly aids even heating for regeneration, defrosting and cooking.
More new microwave-oven technology to combat the variable food density problem involves computer-driven programmes which vary the power output during a reheating cycle. Tony Egan, sales director for Merrychef, says preset programmes for popular menu items represented by push-buttons on the oven control panel mean that a deskilled kitchen can deliver a perfectly reheated frozen food item every time. The Merrychef Menu Key range can store up to 250 programmes on a single key, so that different items can be reheated according to the time of day they are sold.
Typically, in a variable-power reheating programme, there may be a full-power period to heat the outer layers of the food, followed by a period of medium power which keeps heat entering the food while the conduction heats the centre. A final blast may finish off the surface.
While microwave ovens are good at wet products, in their basic format they aren't so good with bakery goods such as bread and pastry. This has led to the development of combination microwave ovens with an in-built grill element to gratin‚e dishes such as a lasagne or with a cavity fan to bake like a mini convection oven.
Typical of this multifunction feature of combination microwave ovens is the Maestrowave series, distributed in the UK by RH Hall. It has nine cooking modes, and a typical cooking time is that for a frozen individual steak and kidney pie, which will defrost and crisp from the freezer in three minutes.
The heating power of microwave ovens is measured in watts, with a typical domestic microwave oven about 800W, while one designed for professional use can be more than 2,000W. The reason why microwave ovens are not manufactured at much more than 2,000W is because the sudden impact of volcanic heat would buckle the food, incinerating the outside and leaving the inside cold, not least because of the 35mm penetration factor into food of microwave energy.
One of the newest innovations dealing with this problem has come from US equipment manufacturer Turbochef. The Turbochef oven is the size of a small convection oven and uses a forced-air fan system to spread the heat from a heating element in addition to microwaves to act as a high-speed convection oven. Among its benefits are that in addition to rapid heat being put into the food, it will bake and crisp and is as happy with fresh food as it is with precooked. The concept of blown air in addition to microwaves is being picked up by other oven manufacturers, with Amana and Merrychef having their own interpretations.
Where the use of microwave technology will fully bridge the gap between tabletop cabinet and the full-size professional oven is in the introduction of a microwave function into combi-ovens. Dutch manufacturer Leventi has been the first with this technology, but all the big global players are looking to merge the microwave oven into the combi-oven.
Terry Ashmore, product development manager for Hobart in the UK, says the race is on for manufacturers to have microwave as a third function in the combi-oven in addition to convection heat and steam, which he says could reduce cooking times by up to 30%.
Also on their way are professional microwave ovens with bar code reader. Frozen food packaging will include a label telling the microwave not just how long to regenerate the food, but the variable power settings needed for perfect regeneration. Now all we need is for somebody to work out how to boil an egg in a microwave oven.
ANATOMY OF THE MICROWAVE
There are clear cooking, construction and food safety differences between microwave ovens designed for domestic use and those designed for catering.
Domestic microwave ovens are often low power, which means they will take far longer to reheat, defrost or cook food than a commercial oven. While domestic ovens have a power rating from 600-900W, commercial microwave ovens can be up to 2,000W.
The device producing the energy waves which heat food in a microwave oven is called a magnetron. Domestic microwave ovens usually just have a single magnetron, while commercial standard microwave ovens usually have two, which are built to a higher specification, making them faster, more efficient and longer-lasting.
Using a domestic model, designed to be used just a couple of times a day, in a commercial environment can lead to a loss of power and all the associated food safety risks.
Microwave energy needs to be evenly spread around the oven cavity to ensure that all parts of the food are safely heated. When chilled or frozen food isn't thoroughly heated, harmful bacteria within the food is unlikely to be killed, leading to a risk of food poisoning. Many domestic microwave ovens use simple turntables to distribute the microwave heat, while commercial microwave ovens have sophisticated heat-mixing systems in the oven cavity.
The casing of most domestic microwave ovens is painted mild steel, which will chip, corrode and cause food safety hazards. Most professional microwave ovens have casings made of hard-wearing stainless steel, which is easy to keep clean and won't corrode.
Source: The Catering Equipment Suppliers Association (CESA)
Contacts
Catering Equipment Distributors Association 020 7233 7724
Amana 01275 343000
Maestrowave 01442 875578
Sanyo 01708 869593
Hobart 07002 101101
Turbochef 020 8686 8855
Merrychef 01252 371000
