Onions and the reduction method

Image courtesy of SteveR

Sometimes you get a good one... one that doesn't make you cry. But chopping onions can be one of the most debilitating jobs in the kitchen. A single eschalot (or Allium cepa var. aggregatum) can bring even the most experienced chef to a blubbering mess. And I use onions almost everyday in my cooking, so it's great to not be brought to my knees everytime I slice and dice.

There are three key tricks to keeping your eyes dry and clear whilst prepping your alliums:

1. Use a sharp knife.
2. Chill the onions before you cut them.
3. Do not stand directly over your chopping surface.

Chemistry / biology
If you look at an onion very closely (you may remember using a microscope in high school) you'll see that like other plants, an onion is made of cells. When you cut an onion these cells are damaged and through a series of chemical reactions, the creation and release of the offending gas, known as onion Lachrymatory Factor or LF occurs. When the LF reaches your face it irritates the eyes. This irritation causes your crying reaction which is designed to flush the eyes of the irritant. Read more here for a good explanation.

Tools of the trade

Using a properly sharp knife reduces crushing of the cells in the onion, reducing the chemical reactions that occur and releasing less LF. Less LF = less tears. This is a simple one. I’ll do another piece on sharp knives at a later date.

More chemistry
Depending on what you’ve done to your brain since, you may also remember from high school science that chemical reactions slow down in the absence of heat. This is because for a chemical reaction to occur, at least two molecules must collide with a minimum of energy. Heat increases the (kinetic) energy of the molecules, therefore increasing the likelihood of these collisions. The more collisions, the greater the chemical reaction and vice versa. Read more here as to why this is the case.

Absence of heat is the key to this, if you chill your onions it will slow the chemical reactions that occur. Less chemical reactions = less LF. Keep just enough onions (I think three of four) in the fridge for your next meal or two. When you use them, immediately replace them with onions from the cupboard and you’ll have chilled onions ready for your next meal.

Stand back
When you are chopping, it’s very easy to stand directly over your cutting surface. This increases the LF that gets to your eyes. Try moving your upper body away from the chopping surface to reduce the LF. The same equations apply as above.

Check out the Onions Australia website for more great information on this invaluable vegetable.