Hi, Can you tell me if the 2 : 1 : 1 ratio of onions to carrots to celery in a mirepoix is by weight or volume? Thank You.

--Pat C

Interesting question! 

The Culinary Institute of America gives a ratio of 8 ounces of chopped onions to 4 ounces each of chopped carrots and celery for a basic Mirepoix, so they are using a 2 : 1 : 1 ratio by weight.

However, Larousse Gastronomique gives the ratio of vegetables as 100 g (4 oz) of onion, 150 g (5 oz) of carrots, and 50 g (2 oz) of celery.  The USDA gives weight for one cup, chopped, of each of these vegetables as follows:

Onions	160 g
Carrots	128 g
Celery	101 g

Using those numbers, the volumes of the ingredients would be about 2/3 cup of chopped onions, 1 cup + 2 tbsp of chopped carrots and 1/2 cup of chopped celery.    In this recipe, the carrots are dominant and nearly double the onios.  Neither by weight or volume is it close to the stated ratio.

The gold standard for home cooks is The Joy of Cooking.  According to the 75th edition, a mirepoix has one onion, one carrot, and one celery rib.  Again according to the USDA, a medium onion weighs 110 grams, a medium carrot weighs 61 grams and one medium stalk of celery weighs 40 grams.  All of the numbers are for the edible portion only.  That would be a ratio close to 2 : 1 : 0.67, by weight.  By volume it works out to 2/3 cup, 1/2 cup, and 6 tbsp, respectively.  Again, not too close to the 2 : 1 : 1 proportions either by weight or by volume.

So, where does all of this leave us?  As a general guideline, use twice the weight of diced onions as you do carrots and celery in making a mirepoix. However (and isn't there always a 'however'?), this is only a guideline.  Depending on what you are making, you may want more or less of any ingredient.  For a tomato sauce, you might choose to up the amount of carrots to compensate for the acidity of the tomatoes.  For a lighter dish, you might want to reduce the amount of onions so as not to overpower other flavors.

I also vary the amounts depending on the vegetables themselves.  If I'm working with the outer stalks of a head of celery, I may reduce the amount because I know those stalks will be stronger flavored and more bitter.  Similarly, when my father-in-law sends home onions, I use less of them because I know his onions are strong!