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Thread: discoloring of onions, blackness

  1. #31
    I have a Nakiri that was very reactive to onions and just about anything else as well. Onions going black and giving off a bad smell was not an option so I just wet an old rag with Rainex( get it at hardware stores in OZ) and let it soak for a few minutes. It took a good bit of the karuchi? finish off and stopped the reaction completely.
    The active chemical is Phosphoric acid, it turns the iron into Ferric Phosphate and creates a non reactive surface layer, lasted about 6 months now and no reaction or rusting at all. I do wipe, wash and dry as on all carbon knives though.
    Hope it helps.
    Last edited by arny1; 03-08-2013 at 07:49 PM. Reason: spelling

  2. #32
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    Arny so u just apply it and it gives u a protective coating
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  3. #33
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    is that stuff food safe? i have no clue.

  4. #34
    Anybody know if this is a problem with the Asai AS Damascus blades? I'm thinking about picking up one of their Nakiri's and would hate to spend a couple of hundred bucks on a vegetable knife that I couldn't use on my favorite vegetables.

  5. #35
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    Thanks all again for the helpful answers in this thread. I was thinking to myself while prepping: What Would Julia Child Do?

  6. #36
    azchef. Yep you can wet a rag and wipe it on, enough that the blade is wet or dip it in a container full. Don't get any on the ferule. Give it a minute or less if you want to check and then rinse it off with water. A good rinse!! It's not applying a protective coating as such, it's more a chemical reaction with ferric oxide converting to a new element? that is not reactive. It will wear off eventually but mine has lasted 6 months used every day at home and its only now that I am starting to think of redoing it.
    A well timed post, need to pull out the stones and sharpen anyway so will do this again tomorrow.
    franzb69. Its used as a food additive and in suppliments but I don't know in what amounts, the surface of the knife wont have much impact on food I think. Maybe someone else can chime in on that.

  7. #37
    Senior Member cwrightthruya's Avatar
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    If all you are after is phosphoric acid....you should be able to do the same thing with Cola... Sans the chemical surfactants, PDMS, Isopropanol and etc.
    At Death's Door You Only Have 2 choices. Die Happy or Die Regretfully.
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  8. #38
    OK I've just got the bottle from the shed, the stuff is RANEX rust buster, available in most hardware stores in Australia. It is 35% Phosphoric acid and only costs a few bucks for 500ml. I don't know what it's called in other countries but something like it should be around somewhere.
    My Nakiri is just a cheap Yamawaku and had a fairly crusty black finish, a minute or so in this RANEX and the finish is a lot smoother and a greyish patina which is fine for me. A bit of thinning behind the edge, treated the blade and then put the final edge on, I still wipe, wash and dry each use and I do put a wipe of protective oil on it every few days but not all the time. As I said, it will stop the onion reaction dead with one treatment and for home use lasts for ages. A pro situation may need more regular treatment but not overly so. I have a white Honesuki that has had the same treatment after it worked so well on Nakiri and it shows no sign of needing another dose(it also does not get as much use though). Test try it on something else if you're not sure

  9. #39
    All the knives that I use are carbon and I have no issues with onions turning black except after a fresh sharpening/patina removal. Usually the first few things I cut (onions/apples) will turn, but that only lasts for a few cuts. Not sure I would want to coat my blades with anything; if it bothered me that m
    once in a while you get shown the light, in the strangest of places if you look at it right

  10. #40
    All the knives that I use are carbon and I have no issues with onions turning black except after a fresh sharpening/patina removal. Usually the first few things I cut (onions/apples) will turn, but that only lasts for a few cuts. Not sure I would want to coat my blades with anything; if it bothered me that much I think I would just use stainless.
    once in a while you get shown the light, in the strangest of places if you look at it right

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