Kitchen Lab: Onions Without Tears?

Big Bowl o’ Onions

Here’s a follow-up from last week’s article on French onion soup.  Ok, I’ll admit it. I was practically weeping like an infant by the time I was done researching this one. Yet for you, dear reader, I mangled my way through a half dozen onions in an attempt to prove which of these purported techniques let you cut onions without crying.

So why does prepping such a basic ingredient make us feel like we’ve entered a tear gas factory? As a defense mechanism, onions absorb sulfur from the soil to create pungent compounds which make them impalatable to the animals who might otherwise want to dig them up and eat them. Each cell in an onion contains not only amino acid sulfoxides, but also a storage vacuole (basically a bag of liquid floating in the middle of the cell) with enzymes. When you break the cell apart, the enzymes mix with the sulfur compounds and produce a volatile gas (propanethiol S-oxide). This in turn wafts up to your eyes where it combines with water to form sulfuric acid. No wonder you’ve got tears!

The good news is that when heated, these sulfur compounds react with each other and with other substances to produce a range of characteristic flavor molecules that give onions the savory, meaty quality which adds depth to so many dishes. So how then to get to this deliciousness without the tears?  Here are the top 10 theories that I tested in an afternoon of not so scientific experimentation:

1. Use a sharp knife
2. Slice, don’t chop

Both of these ideas get at the same general concept, which is that if releasing the onion’s nasty fumes is caused by breaking cells apart, you might want to break as few of them as possible.

Having a sharp knife is a matter of buying the right knife to begin with, keeping it sharp, and honing it before each use. This will leave you with a surgical scalpel which will slice through with precision rather than a dull axe that crushes everything in its path. Likewise, it’s important to use proper cutting technique. If you cut the onion by slicing towards you rather than chopping up and down, you’ll be using physics to your advantage. Think about it:  you can press even the sharpest knife up against your hand and not get cut… just don’t pull it laterally or you’re in trouble!

With this in mind, I tried sharp knife vs. dull and slicing vs. chopping. The results here were incremental, but sure enough sharp knife / slice totally beat out dull knife / chop. As a result, my methodology for the rest of the trials involved beating the crap out of the onion by chopping with a dull table knife.

Conclusion:  The worse I treated my onions, the worse they treated me.

3. Chill your onions

The idea here is that colder temperatures both slow down the enzymatic activity and keep the volatile compounds from launching into the air. There are several suggested methods for this, from putting your onions in the fridge for an hour to popping them in the freezer for half an hour to chilling them in ice water.

This being February, the onions I brought in from the greenmarket weren’t particularly warm to begin with. So, for my test I parked one onion in the fridge and tossed the rest in an oven that had been pre-heated to 200 degrees and then turned off. After an hour, my refrigerated onion was 40 degrees in its center and the others clocked in at a balmy 85. When chopping, the warm onions had a noticeable sting from normal standing distance, but for the chilly onion I had to get my face right next to it to notice anything at all.

Conclusion: Not a bad idea, especially in summer

4. Wear goggles

I tried wearing a pair of utility goggles while chopping and sure enough my eyes didn’t water. Your nose and throat are still at risk though.

Conclusion: Seems to work but you’ll look awfully silly

5. Breathe through your mouth

I tried this while wearing the goggles. I was fine until I took a couple deep breaths through my nose and then the eyes started watering. Your nasal passages have a lot of sensitive surface area so I guess it makes sense to minimize exposure.

Conclusion: These ain’t roses so don’t stop and smell them

6. Ventilate Well

I tried chopping on the counter and then moved the cutting board on top of my range and turned the vent hood up full blast. My vent fan isn’t exactly chem lab quality, so I alternated between pure air and whiffs of onion. Still, this was better than the constant onion fog that I got on the counter.

Conclusion: The better your ventilation, the better this will work

7. Cut under water

Next I tried chopping an onion half in a pan full of water. This worked beautifully as there were no fumes, but as it turns out onions float and this one was constantly trying to get away. If you were doing this in quantity I guess you could scrub down your kitchen sink and submerge a cutting board? In the end, you’re gonna end up with soggy onions.

Conclusion: Seems to work, but a pain in the ass

8. Avoid the base of the onion

So I’ve heard that the base should be avoided becacuse it has more of the active enzyme. I tried alternating between base and rest of onion multiple times, but never really noticed a difference. Then again, the base is relatively smaller so there’s less cut surface area to begin with, and it’s denser so you tend not to cook with it anyway.

Conclusion: inconclusive.

9. Coat your chopping board with vinegar

This one’s kind of geeky. The idea is that the acid denatures the enzyme and prevents the nasty reaction from occurring. So I tried this, and honestly I’m not sure. Maybe if I submerged the entire onion instead of just the parts that are in contact with the cutting board? But then you’d end up with a sour onion.

Conclusion: meh

10. Light a candle

The theory here is that the flame draws in the nasty gases and burns them up. I tried this with a regular votive candle next to my cutting board… and  predictably this was about as useless as using a flame to conjur spirits. Then I fired up a burner on the stove and chopped next to it. This seemed to work better as it created more convection, but I’m still wondering if the onion smell was really just overpowered by the fumes. Also my plastic cutting board may
have started to melt.

Conclusion: Too much of a fire hazard

The verdict

Use a sharp knife and cut by slicing rather than chopping. If you’re cutting a bunch of onions, make sure your kitchen is well ventilated, and if you’re particularly sensitive consider chilling your onions first.

By the way, the ventilation thing especially applies when cooking onion heavy dishes, or else you’ll find that everything you own smells like onion for a few days. I’ve also heard that it’s good idea to keep your dog out of the kitchen lest you end up with a stinky fur situation!

Have you found an onion cutting method that works for you? If so, let me know by dropping a note in the comments.