# discoloring of onions, blackness



## andygraybeal (Mar 8, 2013)

Greetings,
I have a Tojiro Shirogami ITK 240mm knife. It dis-colors my onions. They turn blackish or are dirty looking. I work in a restaurant and the cooks are pissed  What should I do to make this better?

I wonder if i should force a patina with hot vinegar bath or something. Any input would be wonderful... the cooks hate me.
Andy


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## franzb69 (Mar 8, 2013)

a forced patina should help. do you use a damp towel after every few slices to keep the dirt and contamination between other food items down? perhaps coating it with a light film of mineral oil could help. i forced a patina on my 1095 steel chef knife and keep it regularly oiled and that seems to keep discoloration down.

my other chef knife that's monosteel carbon came with a patina since i bought it used so that doesn't discolor food at all. 

let's wait for the others to chime in.


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## Jmadams13 (Mar 8, 2013)

I have a few from that line, so I have some input, and some bad news...

It will probably never stop. I have forced countless types of patinas, and a lot of natural patinas, and they still react like a mofo. How I get around it, dot cut anything with them that's not going to be cooked, unless I'm at home, then I don't care. 

It's even worse after you remove the KU finish. The steel does take a blazing edge though, so its kind of a trade off

Sorry this isn't very helpful, just feel the need to be honest.


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## stevenStefano (Mar 8, 2013)

I've never used a carbon knife that didn't turn onions black. Even knives with heavy months-old patinas and many different steels, it didn't matter. Cut onions with a different knife


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## franzb69 (Mar 8, 2013)

> I've never used a carbon knife that didn't turn onions black. Even knives with heavy months-old patinas and many different steels, it didn't matter. Cut onions with a different knife



my 1095 old hickory after i thinned it and exposed more "new" metal and it turned onions grey. but never black. but after cutting with it more and wiping it down every few cuts then letting the knife steel's patina settle a bit, the reaction pretty much went away. but i just had to be safe and forced a patina anyway.




> It will probably never stop. I have forced countless types of patinas, and a lot of natural patinas, and they still react like a mofo. How I get around it, dot cut anything with them that's not going to be cooked, unless I'm at home, then I don't care.



holy crap on that! i've never heard of knives to get that bad that it won't stop reacting to food. is monosteel shirogami really like that? or is it just tojiro's? maybe it's coz of their heat treat or whatever


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## heirkb (Mar 8, 2013)

stevenStefano said:


> I've never used a carbon knife that didn't turn onions black. Even knives with heavy months-old patinas and many different steels, it didn't matter. Cut onions with a different knife



I'll have to check again, but I think my Marko 52100 doesn't really discolor onions no matter how long the sit. 

As for the OP, I'd get stainless, but that's just me...


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## stevenStefano (Mar 8, 2013)

I've used carbon knives that seemed to be ok, but then the odd time the onions would discolour, which is still unacceptable to me.


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## brainsausage (Mar 8, 2013)

All of my carbons start out this way. IME you just have to put up with it till the patina sets in. Try cutting a lot of raw red meat/hot meats. Seems to help set a patina.


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## DeepCSweede (Mar 8, 2013)

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.


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## Jmadams13 (Mar 8, 2013)

It's not that it's carbon. I have plenty of carbons that don't react. I think just Tojiros white. Only on my ITK line is this a problem. On my 210, Kiristsuke, petty, and 240 gyuto. Some with the KU removed, some not.


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## echerub (Mar 8, 2013)

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.


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## G-rat (Mar 8, 2013)

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...?


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## jgraeff (Mar 8, 2013)

DeepCSweede said:


> 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


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## andygraybeal (Mar 8, 2013)

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


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## Jmadams13 (Mar 8, 2013)

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


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## franzb69 (Mar 8, 2013)

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.


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## Timthebeaver (Mar 8, 2013)

Jmadams13 said:


> 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.


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## Melampus (Mar 8, 2013)

Sorry, but the Tojiro Shirogami ITK is *NOTORIOUS* for its out-of-control reactivity. It's not going to stop.:scared4:


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## kartman35 (Mar 8, 2013)

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??


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## JBroida (Mar 8, 2013)

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


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## kartman35 (Mar 8, 2013)

But the OP says that he washes the knife between vegetables and is still having this issue...Perhaps not often enough?
How often should we be wiping the knife to prevent this? In between each onion? Every 5 onions? Or in this case is it because the specific cladding that Tojiro uses is more reactive than other carbons as has been suggested by some of the replies?


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## Jmadams13 (Mar 8, 2013)

Not quite sure it's only the cladding. I've done tests by only putting the exposed edge into an onion, apple, pear, artichoke heart, and they all turned black or greenish, with only contact with the edge. Yeah the cladding is bad, but that's not the only thing reacting.


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## Jmadams13 (Mar 8, 2013)

Im pretty sure it's possibly a lower quality white steel Tojiro uses in this line to keep the cost low


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## JBroida (Mar 8, 2013)

The more reactive the steel and the more acidic the food, the more wiping


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## kartman35 (Mar 8, 2013)

Jmadams13 said:


> Im pretty sure it's possibly a lower quality white steel Tojiro uses in this line to keep the cost low



Are there differing qualities of white #2? I was under the impression that white #2 is always Hitachi steel company's same white #2...

Or did you mean that the steel was hardened less optimally ?


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## Squilliam (Mar 8, 2013)

Try running boiling water over the knife. It sorted out my stripped 210 ITK.


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## Jmadams13 (Mar 8, 2013)

I've done that too, only worked on the stripped knives. I don't have a problem with it, I've gotten used to it, I just was sharing experiences with the OP. 

I'm not sure of different quality whites, just what I have seen


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## kalaeb (Mar 8, 2013)

Not all white steel is created equal. General wiping should help with black onions. How often do you wipe your blade? When I first get a carbon knife, I wipe frequently until a patina forms. But it sounds like maybe even that is not enough. Good luck


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## Timthebeaver (Mar 8, 2013)

iirc there used to be white #2 type A and B but not any more. All white steels have the same specs for impurities (P and S) iirc, only the carbon content differs ( #1 highest C, #3 lowest).


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## mpukas (Mar 8, 2013)

+1 to the cladding being reactive, in my experience. 

Different carbon steels and claddings are going to react differently with different foods, and will also take patinas differently. The Yusuke white #2 knives I use have built up patina and still have mild reactivity to onions and cabbage. Iron cladding reacts much more strongly than a good quality carbon hagane. KU finish helps reduce reactivity, so stripping yours off only makes it worse. 

I've seen Jon's vid, and I think his suggestion for wiping a carbon blade on a damp towel while cutting reactive foods is a good technique, however, I don't think it's always practical in a pro kitchen if you have to do large quantites - it'll suck up valueable time. Seconds add up. 

I know a chef/owner who won't allow ANY carbon knives in his kitchen, as he doesn't want to risk the reactivity w/ foods. It may be safe, but the off color and odor are not acceptable. 

I'm under the impression that white #2 steel is a product of Hitachi, therefore there are not "other" white steels (same for white #1, white #3, blue #1, #2, #3, etc). But as always I could be wrong... 

To the OP, unfortunately, you may have to look to other options in semi-SS or SS. There are certainly not enough options out there for a carbon core and semi-SS or SS cladding.


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## arny1 (Mar 8, 2013)

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.


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## azchef (Mar 9, 2013)

Arny so u just apply it and it gives u a protective coating


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## franzb69 (Mar 9, 2013)

is that stuff food safe? i have no clue.


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## mkriggen (Mar 9, 2013)

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.


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## andygraybeal (Mar 9, 2013)

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


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## arny1 (Mar 9, 2013)

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.


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## cwrightthruya (Mar 9, 2013)

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.


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## arny1 (Mar 9, 2013)

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


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## chinacats (Mar 10, 2013)

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


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## chinacats (Mar 10, 2013)

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.


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## GlassEye (Mar 10, 2013)

I am not sure if this will work for the knife in question, but this method does work well for all of my carbon knives. When I get a new knife I scrub any patina off with Comet after each use, after some time it will stop forming patina, or at a very slowed rate, and essentially prevent bad reactions with food. The white2 gyuto I have been using for everything lately shows almost no patina, does not react badly, and it has been months since I have scrubbed any patina off.

It does help to keep a damp towel next to your board for wiping the blade.


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## Dave Martell (Mar 10, 2013)

"Tojiro Shirogami"

I've had a few of these roll through the shop, they've all been rusty and stinky. The owners all asked what to do about this and I advised to buy a new knife because I can't believe the problem will stop. I feel the cladding is just too reactive for use as a kitchen knife.


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## JBroida (Mar 10, 2013)

not to sound like a broken record here, but i've used all variety of knives in both home and professional environments (including cheap carbon and very reactive knives)... if you work like i explain in the video, its not really a problem. Stainless makes your life easier, as do less reactive carbons, but pretty much anything should be fine if you pay attention to what you do.

-Jon


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## Chefdog (Mar 10, 2013)

I'm not sure what the steel is, but the Suien gyuto I got from Jon has been surprisingly unreactive. I do wipe it down regularly, but it really is an easy going carbon. I just touched it up before dinner and took the patina off the edge, and the first onion discolored just a little bit. But after that, it was back to normal. Cut some tomatoes and a lime, then had to walk away and grab the kid in a hurry. The knife sat with lime juice for several minutes and there was no noticeable reaction. 
Whatever it is, this carbon is great.


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## Chef Doom (Mar 11, 2013)

Chefdog said:


> I'm not sure what the steel is, but the Suien gyuto I got from Jon has been surprisingly unreactive. I do wipe it down regularly, but it really is an easy going carbon. I just touched it up before dinner and took the patina off the edge, and the first onion discolored just a little bit. But after that, it was back to normal. Cut some tomatoes and a lime, then had to walk away and grab the kid in a hurry. The knife sat with lime juice for several minutes and there was no noticeable reaction.
> Whatever it is, this carbon is great.



+1. I am also a big fan of this knife. My experience is very similar to yours. It's an impressive steel for what it is. I'm going to start recommending this knife as a budget knife in the future.

My recommendation for the OP is to follow Jon's advice along with getting a better quality knife from a different maker if he really wants to stick with carbon. Sometimes in life you have to up the ante in order to come out ahead.


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## Justin0505 (Mar 11, 2013)

+1 to what Jon said.

However, the other thing that I've noticed really cuts down / eliminates over-reactivity is etching. 
Shigefuesa is notorious for using a very soft and very reactive iron cladding and this completely stopped the stinking on mine.

Here's a great post from Dave:
http://www.kitchenknifeforums.com/showthread.php/6474-Damascus-Knives-amp-Re-Etchng

Can can also try soaking it in hot (boiling) white vinegar if you want to just try something simple that you likely have lying around the house first:
http://www.youtube.com/watch?v=DRtEPDzCa2A


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