SHORT REPORT: Combi Testing Leaps Forward

Almost 20 years ago, back in the early 1990s, big retailers were looking for a better way to do chicken—and a lot of other things as well. For many of them, combination oven-steamers, then relatively new in North America, were the answer. They offered great versatility, great finished food quality and precise cooking control.

But how to compare them? No big end-users were going to commit to large numbers of combis without data. But there was a problem—there was no standardized combi test at the time.

Enter Fisher-Nickel Inc., operators of Pacific Gas & Electric Co.’s Food Service Technology Center in San Ramon, Calif. The FSTC had the test facilities and the expertise. The group set about creating a standard.

By ’95, that first method had been ratified as ASTM 1639-95, Standard Test Method for Combination Ovens. Devised as a response to a very specific need—in this case chicken—the test really revolved around the quirky birds.

Testing The Chicken Test

In 2005, the standard was updated with various refinements, and whole chickens (as opposed to breasts) became the test food, but the chicken-oriented procedure was still problematic.

“When you looked at the efficiency data, the numbers were still wobbly,” says David Zabrowski, director of engineering with Fisher-Nickel. “What is combi mode?” he asks, referring to the differences from model to model. Different humidity settings, for example, can seriously skew measurements and calculations.

 “How are combis used?” They’re convection ovens, and they’re steamers, and they’re a blend.

Zabrowski says some of the manufacturers took advantage of such situations, specifying test setups very different from what would be recommended in the field. Optimal energy performance did not line up with optimal food-product results.

“We were getting some great efficiency numbers,” he laughs. “But the chickens weren’t so good.”

And then, again, there were the chickens themselves. “The sizes of the chickens were all over the place,” Zabrowski says. Because of that, the load on the oven was not standardized. To define the problem, the FSTC ran more tests. The team cooked whole chickens from 38°F up to a finished temp of 200°F . Starting weight was measured, ending weight, drippings weight. Evaporation was calculated, energy into the birds, etc.

Sure enough, there were incongruities. Chicken sizes did vary. Load was uneven, ovens with higher humidities added moisture (weight) to the drippings, making them heavier and throwing off energy-to-food calculations. Higher energy-to-food profiles, under drier conditions, generated higher efficiency numbers but also tended to increase shrinkage. In short, the chicken test was just too weird. Efficiency calculations were not reflecting actual oven energy usage.

New & Improved

So now, as of last year, there’s a new test, so different it gets its own number. F2861-10, Standard Test Method for Enhanced Performance of Combination Oven in Various Modes, looks like it solves all the earlier problems.

First change: The food product. The new test method kills multiple birds, so to speak, with a single potato load. First, the variability of the whole chickens is gone. The new test specs steam pans, each with 48 to 52 red potatoes, totaling 8 lbs./pan, give  or take 0.2 lbs. This change alone not only solves the chicken situation, but it specs the same test-food product that convection ovens and steamers use. So test results can be compared not only among combi models in convection mode but also among convection ovens. And ditto for combis in steam mode compared to steamers.

Combi mode, for all its aardvark-to-artichoke variations from model to model, is not measured in this test. Instead, for operators who want at least some kind of a relative measurement of combi mode, testers suggest averaging the data from convection- and steam-mode tests.

In addition to measuring energy and water consumption, cooking uniformity, efficiency, production capacity and condensate temps in cooking performance, F2861-10 of course tests all the usual other functions as well—energy input rate (actual vs. claimed); preheat energy consumption and time; idle energy rate in convection, steam and combi modes; and pilot energy where applicable.

Digesting The Data

Now that 20 combi models have been put through the gauntlet of the new test protocol, you’ll find loads of data and all kinds of differentiations from model to model. But what’s the single biggest thing to look for?

“What’s most significant is the huge range of idle rates,” Zabrowski says. “If there’s one thing to come away with, it’s this: Use smart controls!”

Not only are idle rates all over the board, but consider that combis can spend a fair percentage of their lives sitting at idle. For example, look at the electric models in the table. Look at the idle rates in convection mode—models range from 0.59kW for a 6-pan unit to 2.30kW for a 14-pan model. That’s an idle-consumption spread of almost 4x! And even if you tweak it to account for the larger capacity (2.33x), which might be misleading considering idle is idle, you still get a big 60% disparity.

The spread is even bigger in steam mode, from a low of 1.35kW for that 6-panner to a high of 18.2kW for a 14-pan unit. Again, slice it any way you want, that’s a huge difference.

And in between, there are plenty of models all across the spread. It’s not just a case of one type of combi being different. Group ‘em however you want, and you still have a lot to think about.

Not to put too much emphasis on electric, or on idle rates. Scan the whole table. Differences are similarly broad in gas-models idle rates too, and cooking efficiencies are spread around too.

So the main thing is to study the data and think carefully about how your operations would really use a combi. Will they be idling a lot? Will you need gigantic production capacity and speed? Will you need to trade off production against efficiency? (Probably not in most cases.) If you’re cooking constantly, obviously, idle might not matter as much to you. But realistically, it’s probably an issue to think about.  

And then go hunting. Contact your suppliers. Ask them for their F-2861-10 test data. No doubt they’ll be happy to share their numbers and explain how their models work. If you find a supplier who’s not in the test data here, encourage him to get tested. It’s your money.