discoloring of onions, blackness

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andygraybeal

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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
 
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.
 
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.
 
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'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
 
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...
 
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.
 
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.
 
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.
 
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.
 
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.
 
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...?
 
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
 
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
 
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 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.
 
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.
 
Sorry, but the Tojiro Shirogami ITK is NOTORIOUS for its out-of-control reactivity. It's not going to stop.:scared4:
 
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??
 
They don't have onions turn black... They do exactly what I describe in the video to minimize reactivity.
 
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?
 
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.
 
Im pretty sure it's possibly a lower quality white steel Tojiro uses in this line to keep the cost low
 
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 ?
 
Try running boiling water over the knife. It sorted out my stripped 210 ITK.
 
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
 
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
 
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).
 
+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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