How To Chop an Onion (Step-by-Step Guide)

If you cook then you have to chop an onion there is no way around that. Onions are used in a ton of recipes we make every day. Because of this, you will have to know how to chop an onion. Learning how to properly chop or cut an onion will speed up your prep time in the kitchen. Don’t worry, chopping an onion is not hard. Let’s get started.

Step 1: Trim those ends

You will want to use a sharp knife and then take your onion and trim off both ends. The trick is you want to leave the root intact. So do not cut to far in from the ends.

How to chop an onion

Step 2: Vertical cut through the root

Now carefully hold the onion and take your knife and cut through the middle of the root.  You can make a clean cut through the onion so you are left with two sides.

How to chop an onion

Step 3: Peel the skin off

Using your fingers peel off the outer layer of the onion.  Only peel off the onion you are cutting first.  Leave the other half with its skin on.  This will help with making your eyes burn.  

Step 4: Lay the onion flat side down

Now take your onion half and lay it down flat side down on the cutting board.  You will want to make vertical cuts every 1/4 inch or so apart.  Be sure to leave the root intact as this will be needed to hold the onion together.

How to chop an onion

Step 5: Horizontal 1/4 inch cut

Now, you will want to make horizontal cuts every 1/4 inch down the onion starting at the opposite side of the root.  See the image below.

Dice onion
Onions on table

Step 6: Repeat the same steps for other half

You will now repeat the same steps you did for the first half with the second half.  

Chopped onions

How to chop an onion in a food processor?

Using a food processor is another way to achieve chopped onions quickly.  The process is simple.

Food processor onion chop

Step 1: Peel and quarter onion

Simply cut the ends off again as we did above.  Then you will want to quarter the onion so it fits nicely within the food processor.  

Step 2: Place the quarters into the food processor

Be sure to leave enough room and not to cram too many quarters into the processor at one time.

Step 3: Pulse the food processor

You will want to pulse the food processor a few times first.  Maybe 3 or 4 times to see how small the chopped pieces are.  If you want them smaller then you can pulse the machine again a few times until you get the size you are looking for.

Step 4: Unplug the processor before removing the onion

Be sure to unplug the food processor before reaching into the bowl.  Once you unplug the processor scrape the bowl to remove the chopped onions.  You are done. 

Why onions make your cry?

How to chop an onion

When you cut an onion you damage the cell walls.  When these cell walls get damaged a chemical process releases contents of those cells. 

Now its time to get nerdy.  Enzymes like Amino acid sulfoxides form sulfenic acids as you cut and damage the cells within the onion will mix with the sulfenic acids.  When this happens it produces something called propanethial S-oxide. 

A gas which when it hits your eyes it reacts to the water within your eyes creating sulfuric acid.  This causes the burning session.  

How not to cry when cutting onions

When you cut an onion properly you will have fewer chances of damaging the cell walls which release irritants.  To do this try the following…

  • Start with a sharp knife:  Do not cut onions or anything else with a dull knife.  For one it is more dangerous to use a dull knife because you have to press harder and it could cut you easier.  Also using a really sharp knife will damage fewer cell walls within the onion causing that onion to release fewer irritants. 
  • Cut the onion properly:  Follow the above method.  This will lead to cleaner cuts and allow for fewer irritants to reach your eyes.
  • Placing the cut sides down and away from you:  Once you cut the onion in half place the cut side down on the cutting board.  Also, leave the other side that you are not chopping left unpeeled.  You can also move the chopped pieces into a bowl and move them away from you. 

How long will onions last at room temperature?

Onions are a staple in most recipes and because of this we typically purchase them in bulk or at least 3 or 4 at a time.  It is always convenient to have onions on hand because most of the time are recipes call for them.  With that said there are ways you should store them before use.

What are the ideal conditions to store onions?

Onions like to live in cool, dark places that have temperatures between 45 and 55 degrees F.  If you have conditions like this in your home you could get two or even three months when stored in these cool dry places. 

Depending on where you live you could have a cellar, basement, or garage with these conditions.  However, for those of us who do not we are better off strong onions within our refrigerator for the longest life we can get out of them. 

When put in the fridge how long will onions last?

Whole Raw Onions:

Again, this is not the first place you should be putting your raw onions.  But if you don’t have the conditions we talked about above them the fridge is the next best spot.  When putting whole raw onions into the fridge you can expect to get about two weeks before they start to go bad. 

Sliced or chopped onions in the fridge:

When you have chopped or sliced onions you will want to take them and put them into an airtight container in the fridge.  This will give anywhere from 7 to 10 days when you store them this way. 

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About ASmith

Adam loves cooking and cooking products like cookware, tools, gadgets, and more to help make cooking easier in the kitchen. When Adam is not trying out new kitchen tools in the kitchen you find him researching the next best kitchen gadgets.