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Thread: discoloring of onions, blackness

  1. #11

    echerub's Avatar
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    I generally have little issue with carbon steel knives discoloring my food after a patina sets in. Some are definitely very reactive right off the bat and others seemingly not at all.
    Len

  2. #12
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    On this particular knife it's probably not the core steel that's the problem though right? It's the iron cladding that is particularly impure and full of sulfur. And used because its cheap...?

  3. #13
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    Quote Originally Posted by DeepCSweede View Post
    My 52100 ZK never had an issue so maybe 52100 is a different beast.

    My Shig had some off smells and discoloring in the beginning but I cut a lot of proteins with it and haven't had a problem since.
    nope my new marko custom is discoloring them like crazy right now hopefully after a lot of fabribation today it will stop had to throw them out yesterday

  4. #14
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    thanks for your responses. i'm at work right now. i'll try all of your suggestions to improve the patina. From the guys that say the Tojiro Shirogami ITK knives never stop causing this problem, I hope for my own sake your wrong It's a very affordable knife that i can get really sharp and do so quickly.. i enjoy this part of the knife so much.. I'm going to work hard to keep a patina on.

    Oh and the finish has been removed.

    To franzb69: i wash the knife between vegetables. i prepare a bunch of onions at one time though.. so i don't clean it between each onion.. but I don't think this is what you meant.

    I was hoping that this knife could become a primary knife but maybe not.

    The cooks are wondering what exactly the black is and is it safe to serve if we cook it? Some of them don't think it's safe and would like to throw it out.

    I don't have this problem with my Hiromoto AS wa-gyuto with the stainless clad and the blue inner steel.

    again, thank you for the responses... I'll keep reading the thread and hope for the best about improving the patina... but i understand that it may never help from what a lot of you are saying

    i'm sad.

    andy

  5. #15
    Senior Member Jmadams13's Avatar
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    I hope I am wrong for sake as well, but with my experience, its going to stay. I have been using my Tojiro ITK petty for about two years daily, its almost black with patina, an still reacts to onions, and any light colored doors. Apples are the worst.

    You could try a hot vinigar etch. It helped for a while, but then when other foods kinda clean the patina off, it comes right back.

    Let us know how it goes
    "This is grain, which any fool can eat, but for which the Lord intended a more divine means of consumption.. Beer!" -Robin Hood, Prince of Thieves, Friar Tuck

  6. #16
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    it's just sulfur reacting with the onions. i don't think it's unsafe. just ugly.

    try watching jon broida's video on youtube on handling carbon knives. he suggests having a damp towel on the side of your board so you can wipe the knife down every few cuts or so. might help. i try to do it with all my knives.

  7. #17
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    Quote Originally Posted by Jmadams13 View Post
    I hope I am wrong for sake as well, but with my experience, its going to stay. I have been using my Tojiro ITK petty for about two years daily, its almost black with patina, an still reacts to onions, and any light colored doors. Apples are the worst.

    You could try a hot vinigar etch. It helped for a while, but then when other foods kinda clean the patina off, it comes right back.

    Let us know how it goes

    It's the cladding. You're never going to form a strongly protective stable (predominantly) oxide layer on it, unless you just don't believe in electrode potentials. There's a reason that a lot of soft iron clad kuro-uchi knives (e.g. Takeda) are lacquer coated.

    Put simply, highly reactive soft iron cladding is a poor choice for a general purpose knives (like gyutos/chefs) which are going to come into contact with a variety of foods, unless you don't care about reactivity/spoilage.

  8. #18

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    Arrow >> Tojiro ITK <<

    Sorry, but the Tojiro Shirogami ITK is NOTORIOUS for its out-of-control reactivity. It's not going to stop.

  9. #19
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    So do all agree that this is because of the cladding? I'm currently shopping for a wa-gyuto, and was going to get one in white #2 (not clad). Is this likely to blacken my onions as well? I'd rather get a carbon blade, but if there's no way around the reactivity (someone said use a stainless knife for onions)...I'll go semi or full stainless instead. I'd rather get a knife that takes and keeps an edge as well as possible, but I'm not gonna keep a separate gyuto on hand just for onions...

    Regarding the patina...Someone earlier referred to J. Broida's video on caring for carbon knives...In this video he asserts that pro cooks in Japan tend to keep patinas off their knives because patinas make them look "dirty". How do these guys put up with the black onion syndrome??

  10. #20
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    They don't have onions turn black... They do exactly what I describe in the video to minimize reactivity.

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