When a recipe calls for sliced onions, you have a choice of how to slice them—lengthwise or crosswise.
If you are cooking the onions, as for caramelizing them, you'll likely want to slice them lengthwise, or from root to stem. That way they will hold their shape better during the cooking.
Crosswise cut onions tend to fall apart when cooked. If that's what you want, fine. Just know that onions pieces will hold their shape better in cooking if they are sliced stem to root, and will fall apart more when cooked if sliced crosswise.
If you are adding raw onions to a salad, slice them crosswise. They'll be easier to eat, and they look pretty too!
If you are making onion rings, you'll want to cut the onions crosswise as well.
How to Avoid Tears When Cutting an Onion
Does cutting onions give you tears?
When you cut an onion, it breaks open the onion's cel walls which releases fumes that react with the water on the surface of your eyes to form sulphuric acid. This burns your eyes, which makes you create more tears.
The best way to avoid this is to limit your exposure to the cut surfaces of the onion and to work quickly. Wipe the cutting board down with a sponge or towel as soon as you are finished.
The method shown here for the onion cut lengthwise will help limit your exposure to the onion fumes that make your eyes hurt.
An Onion's Stem and Root End
Before you cut an onion, know the difference between the stem end and the root end of the onion. The root end has a tight root center, which if you don't remove, can help hold the onion together as you cut it.
If the root end is clean, there's no need to cut off the roots. But if there is any residual dirt on the roots, you'll want to slice off the roots, while leaving the hard root core in place.
Article and photos updated, first published 2009
How to Slice an Onion
- 1 onion, any color—red, yellow, white
Method for Slicing an Onion from Stem to Root
Cut off the stem end of the onion:
Cut off the stem end of the onion by about 1/4 to 1/2 an inch.
Trim the roots, but keep the root end intact:
Trim the roots but keep the root end intact. The root end will help hold the onion together as you make the other cuts.
Cut the onion in half:
Place the onion with the cut stem side down on the cutting board. This will stabilize the onion. Cut the onion in half through the root end.
Peel back the onion skin:
Peel back the onion skin and place the onion halves cut side down on the board. If you want, to help keep your cutting area tidy, peel off or cut off the onion skin from the root end.
Slice the onion at an angle:
Cutting along the natural lines of the onion, make angled cuts into the onion, aimed at the center of the onion. Cut almost all the way, but not all the way, to the root.
It will be easier to handle the onion while cutting if the root end stays intact. Space your cuts depending on how thick you want your onion slices to be. More cuts for thinner slices, fewer cuts for thicker slices.
Make a "V" cut: Cut a "V" in the root end to cut away the tough root end
Cut a "V" in the root end to cut away the tough root end that is holding the onion slices together. Then break apart the onion to get the slices.
Method for Slicing an Onion Crosswise
Cut onion in half, root to tip:
Cut off the stem end by half an inch. Cut the root end by 1/8 of an inch, leaving the root core in place.
Place the onion stem cut side down on the cutting board, cut it in half through the root, and peel back the skins as in steps above for slicing an onion root to stem.
Place the onion cut side down:
Place the onion halves cut side down onto the cutting board. Do not remove the skins. Place the onion halves cut side down on the cutting board.
Use your fingers to guide the knife:
Hold the onion firmly with one hand, with the fingers curled inward. With a sharp chef's knife in the other hand, place the side of the blade against the knuckles of your index and middle fingers.
Slice the onion halves:
Use this as a guide as you make slices through the onion. The curled fingers will protect your fingertips from the knife while cutting the onion.
When you get close to the root end, you can hold on to the peeled back skins as you make the final cuts in the onion.
Here's a tip for serving slice onions raw in a salad or sandwich: soak them in a little water with lemon juice or vinegar to remove the harsh bite of the onion!
Method for Slicing an Onion into Onion Rings
Cut the stem:
Cut off the stem end of the onion and peel back its outer peel.
Cut a sliver of onion:
With the peeled onion on its side, slice off a thin sliver from the side. Then place the onion on the cutting board with this thin sliver cut side down.
This will stabilize the onion's position so as you slice the onion rings, the onion will not roll.
Slice onion to make whole onion ring slices:
Curl your fingers inward as you grip the onion to protect your fingertips.
Slice the onion in whatever thickness you desire. If you wish separate the cut disks into separate onion rings.