Friday, October 2, 2009

Caramelized Onions? Not so Fast

A few days ago I posted a question about "caramelized" onions that implied that I was skeptical that caramelization played a role in the development of the flavor of onions cooked until they brown and sweeten. I also asked the same question of Harold McGee, the author of the popular food science and history book "On Food and Cooking." Based on his response it seems that it is by no means obvious that caramelization plays a role in the development of the flavor of browned onions. That said. why are they called 'caramelized onions?"

Follows my question and Harold's response.

I wonder if any of you know if (the sugars in ) onions actually caramelize when they brown. I have never detected the aroma of caramel in what most people call "caramelized onions" and for a long time have assumed that folks mistake the effects of maillard reaction and the concomitant increase in sweetness due to concentration of sugars via evaporation for caramelization. What do you think?

"I think you're right that the browning is mostly Maillard, and that the sweetness is what takes people to caramel. But if you brown in butter, you'll get some aroma components in common with caramelized sugar (and of course caramel), so maybe that's part of it too. "


natalie sztern said...

if i let onions get too brown the 'burnt' bits taste so sweet there is actually a hint of that sticky caramel texture. but they have to be almost burnt and that ususally is not an all around tasty dish...the burnt bits are ok when they hover on the ouside edges

Mike Pardus said...

If you evaporate the water, concentrate the sugar and heat past 310F, you are caramelizing - no? You know I don't care if I'm right or wrong in this, it just makes rational sense to me and I'll need a rational answer to change my perspective.Also - are onions higher in protein than in sugars? If so, that would be surprising.

Ed Bruske said...

I'm with Mike on this. Of course, it would take a chemical analysis. But I suspect there are more sugars in onions than protein. An extended browning of onions develops sweetness, not the baked bread effect one normally associates with Maillard.

Bob del Grosso said...

That's great "common sense" but until some does hard science and tests for caramel compounds we don't know. Which, of course, is precisely my point. If no one really knows whether or not caramel is produced when onions brown, then why the F--K do we call them caramelized onions?

I spent some time searching for anything that addressed the question (Do onions caramelize?) and found nothing, nada, zippo.

I'm not drawing any conclusions yet.

Scotty said...

I don't care too much how this comes out - I just like having a home that makes me think about stuff like this. It's fun!

Chojinchef said...

For what it is worth: There is a 7 gram to 2 gram ratio of sugar to protein in raw onions. said...

Is onion "caramelization" facilitated if the onions are dusted with baking powder? Does a dusting of cream of tartar interfere?

In principle, an alkaline environment should promote the maillard reaction; I don't see that it would have an obvious effect on pyrolysis of sugars.

I'm a chemist, or used to be, but this is way out of my field. Still, it's the sort of clue that might be familiar to people who cook a lot of onions.

Bob del Grosso said...


The little bit of research I have done on this subject seems to support the idea that caramelization of sugar is more rapid at high (basic) pH. The same is true of the family of reactions (enzymatic, nonezymatic, high moisture, low moisture) Maillard reactions.

I would not be at all surprised if science does not someday soon show that caramelization often precedes or follows Maillard browning reactions when there is sufficient sugar present and when temps reach levels required to effect pyrolysis (of sugar).

There are just too many "browned" foods that have flavor profiles that show aromas that are not normally associated with simple sugar that has been caramelized and where. like "caramelized onions, " the caramel aroma is apparent.

Gary Allen said...

One of the compounds formed as sugar caramelizes is diacetyl. It smells like melted butter, because butter also contains diacetyl (in very minute quantities -- it's acrid and very nasty at higher concentrations). Which is to say that McGee -- as usual -- is right on target.

As for the mis-use of "caramelization," it's so rampant -- even among chefs who should know better, let alone FoodTV celebrities who have staffs that should know better -- that I no longer fly into a rage when I hear it. A barely audible "tsk tsk" is all that escapes these lips.

what said...

I too was looking into this and can't find any science behind it.

Put a sliced onion in a pan with fat on 20% heat and compare it to a peer with no fat. What happens is completely different. And at that low heat, can it really be caramelized?

It certainly browns a lot in the oil, and very little alone.

My impression now is that the oil conducts heat more readily to the onion biomass, causing water to more rapidly escape, and causing the vagaries of the biomass itself (not just the sugar) to burn and turn brown, even at that low heat. But I don't see JUST or even PRIMARILY the sugar being responsible.

But I'm not an expert and because of the lack of experts I've got to speculate. This is a pressing matter indeed