What is a combi microwave, and what does a steam oven do?

They are two different attempts to combine cooking methods in one appliance, and they solve different problems.

A combination (combi) microwave adds conventional heating to microwave cooking.

Microwave alone heats food quickly by exciting water molecules throughout the food, but produces no browning — the surface never gets hot and dry enough for the Maillard reaction, which is why microwaved food is pale and soft.

A combi adds a grill, a convection element, or both, so it can brown and crisp. Used together, the microwave heats the interior rapidly while the conventional element browns the outside — a roast chicken or a jacket potato in a fraction of the usual time, with a proper skin.

Where combis suit people: small kitchens, single-oven households, and anyone wanting one appliance to reheat, bake and roast. The compromises are real: capacity is small, results in convection mode are generally not quite those of a full oven, and the controls are frequently confusing.

A steam oven injects steam into the cavity, either from a refillable tank or a plumbed supply.

What steam does. It transfers heat efficiently while preventing moisture loss. Food cooks without drying out, vegetables retain colour, texture and water-soluble nutrients better than when boiled, and reheating leftovers is dramatically better — bread, rice and roast meat revive rather than turning rubbery, because the moisture that would otherwise escape is replaced.

Combination steam ovens (combi-steam) are the more capable version, alternating or combining steam with conventional heat. This is a professional technique now available domestically: steam during the early phase keeps meat moist and allows bread to expand fully before the crust sets, then dry heat browns. Bread baked with steam injection develops a crust and rise that a domestic oven cannot otherwise achieve.

The costs: price, descaling maintenance in hard water, and tank refilling on non-plumbed models.