Dicing for flavor: an experiment in onion preparation

I was recently regifted “The Science of Good Cooking,” Cook Illustrated’s guide to several kitchen principles.  “Yippee!” I thought. “A book full of principles to try to prove wrong.”

I immediately homed in on a chapter entitled “Slicing changes garlic and onion flavor.”  The chapter was interesting most of the odor from onions and garlic occurs after you chop the vegetable and rupture the cell walls. When the cell walls are ruptured, a sulfur-containing amino acid combines with an enzyme, producing a new compound that is responsible for the characteristic onion/garlic smell and flavor.  What this means is that onion doesn’t taste like an onion until we chop it up.  What this also supposedly means is that chopping an onion in different ways will make it taste more or less oniony.

I was skeptical that the way I chopped an onion could meaningfully affect how it tasted in a recipe. I had no doubt this cell-wall-rupturing story was true, but can different onion chopping preparation have a big enough effect to change the flavor of a recipe? Experiment time.  I decided a would prepare a recipe that depended largely on onions for its flavor and chop the onions three ways to see how much the way the onion was chopped would affect the flavor.

The Recipe

The Recipe - dicing of flavor

I had a ready recipe in mind for this experiment- my beloved kale salad dressing. My girlfriend perfected this recipe from the hippies of Big Sur (no joke).  But it’s so simple I’ll just list it right here:

  1. Thinly slice an onion.
  2. Let the onion slices soak in a marinade that is equal parts lemon juice, olive oil, and Tamari soy sauce.
  3. After an hour or so, pour the onions and marinade over a freshly chopped bed of kale.

The key part of the recipe was in the onions, which softened and absorbed most of the flavor of the marinade.  I thought that if the chopping method was likely to affect any recipe, it would be this one.

So I prepared the onions three ways (as shown in the picture at the top): diced, sliced, and coarsely chopped.  I put each in a separate mug to marinade for about an hour and a half and then tasted. Due to the difference in shape, a blind taste test was impossible (you always knew which test you were eating, even if you closed your eyes).  I did employ another taster besides myself, and to be fair we were highly biased against finding a difference.  We both thought the Cook’s Illustrated article was interesting, but not important enough to affect the taste.

flavor observation in recipe

Observations

The first big observation was that the sliced onions (the ones in the actual recipe) were the most difficult to fit inside of the mug.  I knew that they wouldn’t all fit in the marinade and would require occasional stirring from previous kale salads. But what was surprising was how well the other two tests fit inside the mug, despite having the same total mass of onions. Squares and little pieces are much easier to pack together than long, curved strands. Why did the creators of the recipe decide on sliced onions then?

The next interesting observation was the appearance of the three tests, post marinade.  Both the diced and sliced tests were well softened and browned, as both had a pretty high surface area to volume ratio making it easy for the marinade to completely penetrate through the onion pieces.  But the chopped onion had a distinct white center through which the marinade had not completely penetrated, and was not quite as softened as the other two preparations.

recipe flavor dicing obersvation

Taste Test

Ok, the big surprise: we noticed a difference in taste between the different onion preparation techniques.

  • The most coarse, chopped onion pieces were described as more oniony and blander.
  • The long thin slices we described as saltier, and the most balanced.
  • The diced onions were described as sweeter but sour and a bit lemony.

One taster preferred the sliced onions, and one preferred the diced, but both indicated that those variations were pretty similar and much better than the coarsely chopped onions.

The taste test was done by tasting the onions directly. Once mixed in with the kale and eaten as a salad, the additional flavors of the kale mostly masked the differences between the onion preparation techniques.

conclusion of experiment

Conclusions

Well, darn.  Cook’s Illustrated sort of has this one right.  There seems to be a difference in flavor between the different onion preparation techniques. This flavor is likely caused by the effect that Cook’s noted—the more finely chopped, the more cell walls ruptured, and the more flavor compounds produced. Of course, in this particular recipe, the more finely chopped also meant the more absorbed the marinade would be.  But even between the diced and sliced onions in which the dressing appeared fully absorbed, a somewhat subtle difference could still be noted.