These convection steam oven models typically offer the option of cooking with hot air, steam, or a combination of the two. Some can also be programmed to switch between those modes during one cycle, providing the perfect moisture level in every step of cooking.
Benefits of the Combination Oven
They're numerous, to be sure, but one of the most noticeable advantages is the ability to quickly provide well-cooked foods, even at high volumes. Steam releases its heat immediately on contact with food, which means it provides very fast cooking while keeping your foods moist. Though not quite as effective at this type of cooking as a dedicated steamer, these still give the benefits of it. Likewise, they provide efficient cooking through convection, which helps eliminate hot and cold air pockets. Both of these methods are known for speeding up cooking and providing consistent results, so combining them only builds on the strengths of each.
Finding the Right Size
For most kitchens, capacity will be one of the main considerations. One of the biggest benefits of these is that they combine the operations of two other types of cooking equipment. On top of that, they can also provide considerable capacity in that space.
The convection steam oven is evaluated by whether it will accommodate full-size (18x26) or half-size (18x13) sheet pans. Each type will fit full-size hotel or steam table pans, which measure 12x20. Which one you choose may be as simple as knowing which your kitchen typically uses. If it's not, full-size units are likely to offer higher capacity than similar half-size ones, so keep that in mind if you need more output.
It's important to note that you may need different types of pans for the various cooking methods offered by a combination oven. If you're roasting or baking large quantities of food, you'll probably want to get a hotel pan that offers plenty of room within its solid walls. Steaming is best done with a perforated steam table pan, which exposes more of your food to the humid air. Baking items like cookies and pastries, as well as roasting larger cuts of meat, is best done on a sheet pan.
This is the most obvious way of judging the capacity of a convection steam oven. In theory, you could put a sheet pan on each of those levels, but that isn't a good idea because it wouldn't allow room for the air circulation that is critical in cooking. So, don't think of pan levels as a direct measure of how much capacity a given unit offers, though it does give you an idea of the size of the cabinet.
Pan levels are more important in knowing how much versatility you'll have in preserving the air flow. More levels means more options for where you put your pans, so you can space them out as needed to provide the cooking required.
Some manufacturers offer models that essentially come with a combi oven on top of another, doubling your capacity out of the crate. If you bought a single unit and have since realized you need more capacity, most models are stackable, so you can add that cooking room easily.
The Steam Story
When it comes to the humid cooking side of these units, there are a couple things to consider as you make your buying purchase. They'll impact both the type of steam produced by the model you're considering and how it's produced.
Steam Source: Spritzer or Water Reservoir
Where the steam comes from affects how much of it is available in your cooking. The source also impacts how much water the combination oven in your kitchen will use.
A spritzer, also called a flash pan, introduces moisture to the air by spraying water onto a hot metal surface. That may be a metal plate dedicated to that job, the wall of the oven, or even the convection fan. These are good for kitchens that don't do heavy steam cooking, as these provide a less intense steam. One of their best applications is roasting meat, as they provide consistent heat and enough moisture to keep it from drying up or shrinking.
Units with a water reservoir at heat that water to produce steam that is vented to the cabinet. The steam level can be controlled by changing the heat under the pot and by varying the number of elements that are on. These units provide a more intense steam. They're good for serious steaming of foods like vegetables and fish, but can be a bit less forgiving than spritzer models. While their steam is more consistent, they do have some drawbacks, including higher water usage and more intensive cleaning needs.
Both boiler-based and boilerless convection steam oven models are available. In reality, both types have some sort of broiler that holds water for producing the steam. The real question here is whether that broiler is enclosed or if you can access it.
In a boiler-based convection steam oven, the water storage is closed off to the user, typically in the bottom or sides of the unit. This type provides more heating power and a more consistent steam. If you need to be able to steam foods all day long, this is going to be the better option. These will have a condensate drain, a hole at the bottom of the cabinet that releases the hot water produced by the condensation of the steam in the cabinet. Because of codes that restrict how hot water can be when it's put into public sewer systems, these will need a second water line run to them for cold water to reduce the temperature of the run-off before it drains. That means these will use a lot more water than boilerless units. These can also require regular maintenance calls, particularly in areas with high mineral content in local water supplies, because deposits can build up in the enclosed boiler and hamper the operation of the unit.
Boilerless models will typically have an open reservoir in the bottom of the cooking compartment, with most units shipping with some sort of removable cover for that tank. The steam is either produced by heating that water and allowing steam to rise off it or by sending the water to spritzers. These provide a dryer steam, which makes them great for jobs like baking bread and keeping roasting meats moist. However, they're not going to be very good at keeping up with high steam demand or preparing foods like steamed vegetables or fish.