discoloring of onions, blackness

[arny1]

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.

 

[azchef]

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

 

[franzb69]

is that stuff food safe? i have no clue.

 

[mkriggen]

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.

 

[andygraybeal]

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

 

[arny1]

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.

 

[cwrightthruya]

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.

 

[arny1]

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

 

[chinacats]

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

 

[chinacats]

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.

 

[GlassEye]

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.

 

[Dave Martell]

"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.

 

[JBroida]

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

 

[Chefdog]

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.

 

[Chef Doom]

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.

 

[Justin0505]

+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