Most recipes call for onions when marinading steak, but...why?

  • 1
    Good question. While I'm not sure, I'd be inclined to think onions contain an enzyme that help tenderise the meat. The cooking together may even help activate the enzyme. In a similar role, pineapple is used to tenderise gammon steak.
    – Noldorin
    Commented Oct 10, 2010 at 19:06
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    Onions do not contain such enzymes.
    – daniel
    Commented Oct 10, 2010 at 21:20
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    Marinade on a good steak does nothing but help you ruin it. Good quality steak, high heat and maybe, just maybe salt and pepper is the way to go. Maybe a flank or something but what kind of steak are we talking about ?
    – Chris
    Commented Oct 11, 2010 at 0:29
  • there is sugar in onions, it might help brown the meat when grilling.
    – Max
    Commented Jan 26, 2016 at 13:35

7 Answers 7


Because onions contain a lot of flavour compounds that we like, and which are synergistic with meats.

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    In other words, there's no functional reason for this ingredient, it's purely for flavour.
    – Aaronut
    Commented Oct 10, 2010 at 21:57
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    Yup, it's just taste. Onions don't tenderize meat. Commented Oct 11, 2010 at 13:40

Onions contain proteolytic enzymes, just like honey and certian fruits, which makes them ideal to help tenderize meat. They are a very common type of vegetable that's low in calories, and have a place in nearly every cuisine around the world.

One prime example is a dish from Japan known as Chaliapin Steak, which is a dish where you score the meat (make grid lines), pound the beef, and cover both sides of the steak in chopped onions. Just letting the steak sit in the onions makes it so tender you can cut it with a fork or chopsticks.

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    Reminds me of "Shokugeki No Soma: Food Wars." Everything you brought up was a part of the anime. :D
    – Jay
    Commented Aug 7, 2015 at 17:41

In this study they compare using onion with meat over a roughly 30-day period in refrigeration. At the 30-day mark they have a sensory panel compare the 30-day vs non-onioned 4-day meat. The sensory panel concluded there was no significant difference, but a small fraction preferred the onion meat (30-day). This can suggest onions also have enzymes that inhibit lipids to improve longevity.


Peeling, cutting, or crushing an onion's tissue releases enzymes called allinases, which convert amino acid sulfoxides into sulfenic acids. The sulfenic acids, in turn, form a mixture of products that includes syn-propanethial-S-oxide (the chemical that triggers tears). This mixture contains the precursors for a variety of compounds that form the flavor of onions. They also form the odorous thiosulfinates (the pungent odor associated with chopping onions).


Since onions contain acids, and acids break down the muscle fibers in meat, onions can be used to tenderize meat.

You can also use fresh pineapple juice (canned won't work), lemon juice, lime juice, orange juice, vinegar, or yogurt to tenderize your meat. Some of my friends use tea, coffee, or Coke.

As long as it is acidic it will work.

Please remember, everyone's taste is different, so how long you should marinate the meat takes some experimenting. Start with 20 minutes and work up from there.


Actually, yes the onions are there to add flavor, but they also contain enzymes that break down the meat fibers making it more tender, this can also be done with pineapple and other fruits like kiwi. But the fruits add a fruity flavor which doesn't taste good to most when eating a steak.

Onions however, add a much more savory flavor. @Chris - Marinading a good steak doesn't ruin it, all it does is add flavors that weren't there before. Now granted one can buy some A3-A5 beef and have an extremely tender steak, but you are paying a lot of money for that meat. Marinading is a flavorful way to make very tender steaks at half the cost (OR LESS!)

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    What enzyme is in onions that has a tenderizing effect? i have never seen this claim before.
    – SAJ14SAJ
    Commented Feb 19, 2014 at 18:54

Technically onions have special enzymes that are used to break down protein, so when we put it on steak or any other protein it makes the meat tender as well as soaking the taste of the onions into the meat.

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    Yamada Tojo, welcome to the site! Please don't repeat previous answers, Stack Exchange works different from many forums you might be familiar with. We upvote existing answers instead of repeating them. To learn more take the tour and browse our help center.
    – Stephie
    Commented Jul 19, 2016 at 21:44

Onion contains an enzyme called or chemical named tridyhydrochrmiderm not sure about the spelling but it breaks down meat much like a spider does it's food ..its really cool watching this take place...it's way better in studies then any placebo could ever be...

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