Honestly I have never had an odor problem from all the ones I freeze diced while fresh in freezer bags. But I sure don't know of any reason why you couldn't do as you describe - cook and then freeze. Mushier when thawed of course but no safety issue.

Dave

I don't have a problem with the odor either, but maybe just not as sensitive to it. Or, the fact that I love the smell of onions, it doesn't bother me!

They're really only suited for cooked dishes after thawing anyway, so why not cook them down.
It may be a little more difficult to take out small portions later, but you could freeze in a thin layer on a cookie sheet, break apart and freeze. Then just break off what you need later.

Deanna

I have to put mine in a large plastic food storage container with a tight lid.
Otherwise they smell up the whole freezer.

Why not triple wrap them in plastic grocery bags?

Don't use grocery bags as they are not food safe. They may contain harmful chemicals that could leach into food.

It is better to use food safe plastic freezer bags, or better yet, aluminum foil. Stick the onions in the foil, fold seams, then crunch tightly. Pop into a freezer bag. You may have to re-wrap or use a new piece of foil after they have been opened a few times. You could also make small packets of, say, a cup each - depends on how much you use at one time. Put the packets in a 2-gallon plastic zippered freezer bag.

Nancy

This seems to depend on the variety of onion, or what stage it was when chopped up and frozen, or some other factor. Because some times, no matter what I wrap chopped onion up with, the whole freezer reeks of Eau d'Onion and that smell seems to permeate everything else in the freezer. Other times, its no problem at all.

Right now, I've several zip lock freezer bags of chopped onion that don't smell a bit.

But to address the question - we have browned / caramelized quantities of onion and frozen the results - this cooking process seems to get rid of what ever compound it is that smells so strongly. Frozen in rough quantities of a cup, we add it to soups and stews for that special flavor. Works very well with leeks.

Most of my vegetable freezing is done in half pint and pint - stackable freezer containers. I freeze a lot of recipe-size things - first placed in small sandwich freezer bags - then placed into larger sized rigid plastic containers - double bagging more-or-less. In this way, I can open the rigid container, remove a bag and close it again, without risking the rest of the contents.

This works well with such things as dehydrated toms, bananas, plums, nuts, etc.

It might be worth a try with your onions - packed in individual sandwich bags, then the larger size hard plastic - might keep the odors from escaping.

Bejay

All plastic, including the best freezer bags, will leak out onion smell over time. So what I do to eliminate the order is put about one cup of onion into a snack bag, then put three of those bags into a quart freezer bag, and then stack the freezer bags inside a METAL container. Those large three variety popcorn tins that you see at Christmas time work excellent! The metal will contain the smell, and your freezer will not smell of onion at all.