What revision is "How To Brew" up to these days? 6? 7?
Cheers!
Cheers!
We don't seem to have any chemists here, at least none that chose to reveal themselves, and metallurgists (like Palmer) are apparently not good enough... ;-) Brewers are a tough crowd.
Surface wear due to cleaning and disassembling/reassembling of various parts would be my first guess. Although if you only CIP (either with a spray ball or a full soak) and never disassemble anything (not a good idea unless you're 100% sure that dirt cannot collect anywhere no matter what) I suppose you could go decades without further treatment.My curiosity lies in this: If you are not using heat, ie: using a vessel for fermenting, what would cause iron to make it back to the surface?
Surface wear due to cleaning and disassembling/reassembling of various parts would be my first guess. Although if you only CIP (either with a spray ball or a full soak) and never disassemble anything (not a good idea unless you're 100% sure that dirt cannot collect anywhere no matter what) I suppose you could go decades without further treatment.
I don't know of any published scientific evidence to answer these questions. I've heard "expert" opinions range from the oxide layer forming instantaneously upon air exposure to several weeks.
- I would think that repassivation of chromium is a lot faster if a strong oxidizing acid is used. This conversation could benefit from discussion of redox equations and/or ORP values
- I wonder if something simple, like hydrogen peroxide, would accelerate the repassiviation of the chromium after an acid was used to remove free iron.
Theoretically, chloride (present in wort/beer) or chlorine compounds (often present in tap water) can damage the passivation layer, as can some cleaning compounds. Furthermore any mechanical scrubbing, scrapes, or scratches can possibly expose surface iron. I know off hand that there are in fact published studies that show that the presence of stainless steel can affect H2S production during fermentation, which proves that the oxide layer can be penetrated under normal circumstances and therefore passivation can have an positive impact.If you are not using heat, ie: using a vessel for fermenting, what would cause iron to make it back to the surface?
Theoretically, chloride (present in wort/beer) or chlorine compounds (often present in tap water) can damage the passivation layer.
That makes sense. If someone would tell me that scrubbing or scratching SS would lead it to rust, I’d say I disagree. You can grind SS down as much as you want and it will not rust when exposed to water/air. But as I expected, in brewing the worry is not rust but rather the effect trace amounts of iron may have on the beer.
Damn that's some fancy grade TIG work right there
Turbo displacement looks bigger than that 4 banger
Cheers!
Maybe some day Palmer will learn about Fenton reactions just as he eventually learned about passivation.
No it isn't.But as I expected, in brewing the worry is not rust but rather the effect trace amounts of iron may have on the beer.
No it isn't.
Can the heat from a propane burner also remove or damage the passivation on the inside of a brew kettle? If yes, is there any point in passivating a direct fire stainless brew kettle? If chloride can also damage it, I guess I'd further question whether there is any benefit in passivating any brewing equipment that will be holding wort at high temperatures.
The reason I ask is that I've attempted a few times (unsuccessfully) to passivate my brew kettle and other stainless cooking pots when I've noticed the "rainbow" effect inside at the bottom. Followed the citric acid process outlined earlier in this thread (completely clean with PBW, soak in 5% citric acid at ~150F, rinse with DI water, air dry for a couple weeks). Everything looks like nice, clean, shiny stainless when this is done. But on the next brew day or next time I cook with my stainless cookware, the rainbows at the bottom are back, which I'm guessing is some form of oxide layer formed by a reaction between the stainless and whatever food or wort it was holding. If it's due to the stainless reacting with something, then I'm assuming that the stainless was not passive, at least under the conditions that it was exposed to. I think this tends to occur with acidic things more often, but not sure about that.
Since I only see the rainbows on the bottom where the heat is applied, is this inevitable when applying direct heat to the exterior of the stainless vessel? Or is all my stainless brewing gear and cookware made from cheap quality 304 stainless that can never really be passivated? Is removing whatever it is that is forming the rainbows on the stainless doing more harm than good, since it means that the reactions will happen again on the next brew? Lately, I've just been leaving it alone thinking that if it's already reacted and formed whatever oxide layer it is that gives the rainbow colors, it may be best to leave it there so that it doesn't have to reform again like it would after removing it and re-passivating the stainless. I noticed this happen in stainless that is not directly heated, so I'm assuming that temperature must be involved, which makes me question whether there is any benefit to passivating stainless equipment that will be heated.
Corrosion.Then, what is the concern?
Corrosion.
Corrosion.
Last week I drained the kettle, the insides looked like a rainbow. It looked absolutely horrible. Not like a light tint of a rainbow. It looked like a mood ring on drugs.
And you didn't include a picture?
The citric acid passivation method was actually discovered in an attempt to prevent surface iron from affecting beer flavor.Corrosion.
Your kettle has "heat tint", which is from the chromium being affected by high temperature. At some point the kettle was probably heated while empty. Passivation (which removes only iron) will not fix it.Can the heat from a propane burner also remove or damage the passivation on the inside of a brew kettle? If yes, is there any point in passivating a direct fire stainless brew kettle? If chloride can also damage it, I guess I'd further question whether there is any benefit in passivating any brewing equipment that will be holding wort at high temperatures.
The reason I ask is that I've attempted a few times (unsuccessfully) to passivate my brew kettle and other stainless cooking pots when I've noticed the "rainbow" effect inside at the bottom. Followed the citric acid process outlined earlier in this thread (completely clean with PBW, soak in 5% citric acid at ~150F, rinse with DI water, air dry for a couple weeks). Everything looks like nice, clean, shiny stainless when this is done. But on the next brew day or next time I cook with my stainless cookware, the rainbows at the bottom are back, which I'm guessing is some form of oxide layer formed by a reaction between the stainless and whatever food or wort it was holding. If it's due to the stainless reacting with something, then I'm assuming that the stainless was not passive, at least under the conditions that it was exposed to. I think this tends to occur with acidic things more often, but not sure about that.
Since I only see the rainbows on the bottom where the heat is applied, is this inevitable when applying direct heat to the exterior of the stainless vessel? Or is all my stainless brewing gear and cookware made from cheap quality 304 stainless that can never really be passivated? Is removing whatever it is that is forming the rainbows on the stainless doing more harm than good, since it means that the reactions will happen again on the next brew? Lately, I've just been leaving it alone thinking that if it's already reacted and formed whatever oxide layer it is that gives the rainbow colors, it may be best to leave it there so that it doesn't have to reform again like it would after removing it and re-passivating the stainless. I noticed this happen in stainless that is not directly heated, so I'm assuming that temperature must be involved, which makes me question whether there is any benefit to passivating stainless equipment that will be heated.
Haha thanks! That manifold went to a customer in Cyprus. The turbo was sized to make 900+ bhp on a stroked 1.8T Audi A3! Good times.
Your kettle has "heat tint", which is from the chromium being affected by high temperature. At some point the kettle was probably heated while empty. Passivation (which removes only iron) will not fix it.
I've never passivated mine but I did get it second hand.Personally I think it's just the thickness of the passive layer that can cause different colors because of refraction. If you look up colored stainless you will find companies that sell sheets with a range of colors and the process to make it involves thickening the chromium oxide layer with different treatments. I have two identical 10 gallon kettles, one I do my passivation runs in and and the other just standard brewing duty. You can guess which one has a faint blue rainbow color to it.
I've never passivated mine but I did get it second hand.
Personally I think it's just the thickness of the passive layer that can cause different colors because of refraction. If you look up colored stainless you will find companies that sell sheets with a range of colors and the process to make it involves thickening the chromium oxide layer with different treatments. I have two identical 10 gallon kettles, one I do my passivation runs in and and the other just standard brewing duty. You can guess which one has a faint blue rainbow color to it.
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