Sulfuric acid addition and copper coil -- beer ruined? (with pictures)

[zdegner]

This past weekend I brewed a pilsner and tried something slightly different this time. I used 1 ml of 98% sulfuric acid in 40 L of sparge water to drop the pH to 6.0 (used Bru'n Water for the calculation). Normally I do not treat my water, other than adding half a campden tablet.

In my current setup the wort is circulated through a copper coil in the HLT to keep it at the target mash temperature. This time though, after the water had drained from the HLT for sparging, I pulled out the copper coil and lo' and behold:

BLUE!

I took this picture today. The colors have darkened a fair bit over the past few days. When I first pulled the coil out it looked almost like it was covered in oil -- somewhat multicolored, but with something of a blue tinge to it. This got me concerned.

After scouring these forums and the internet, my theory is that the dilute sulfuric acid solution probably reacted with the oxide layer on the copper and formed copper sulfate (toxic). It doesn't sound like the dilute acid solution could react directly with the copper itself, but once the sparge water started to drain away, I'll bet the copper started to oxidize again and then reacted with the acid left on the surface.

Does this theory seem right? Do you think the beer is ruined? The fermentation seems to be progressing normally and the beer looks and smells normal. Any other theories?

(A friend of mine is a chemist, he took a sample of the wort today and plans to measure the amount of copper in there. Should have some figures in a day or two.)

 

[Homercidal]

Odd. 1 ml of sulfuric acid doesn't seem like much in that much water. I know chillers can end up looking a bit ugly out of the wort, but I don't know about a blue color. My PCB etching solution is green, not blue.

Supposedly the yeast can eat a certain amount of copper, that is why many boil kettles are made of copper (or were, before SS) but I'd be leery of that much going into a beer.

 

[ajdelange]

This past weekend I brewed a pilsner and tried something slightly different this time. I used 1 ml of 98% sulfuric acid in 40 L of sparge water to drop the pH to 6.0 (used Bru'n Water for the calculation).

So the alkalinity of your water is about 75 ppm as CaCO3? The reason for asking this is that 1 mL of conc. H2SO4 would bring water at that level of alkalinity to pH 6 but if the alkalinity were only 50 it would take the water to pH 5. FDA doesn't worry much about pH and copper until the pH gets below the range that is typical of the hot side of brewing. So if your treated water's pH were above about 5 the FDA would bless what you did and you would have nothing to worry about. OTOH if you mismeasured the alkalinity of your water or the amount of acid in the wrong direction you would lose the FDA blessing though I rather doubt that a single exposure would bring you to grief.

BLUE!

The tarnish on copper can contain lots of stuff depending on what it has been exposed to. Cupric ions are intensely blue if water is around.

After scouring these forums and the internet, my theory is that the dilute sulfuric acid solution probably reacted with the oxide layer on the copper and formed copper sulfate (toxic).

Copper sulfate is soluble. Sulfate ions certainly aren't toxic (at reasonable levels). It is the copper itself that is of concern or rather copper ions here.

It doesn't sound like the dilute acid solution could react directly with the copper itself, but once the sparge water started to drain away, I'll bet the copper started to oxidize again and then reacted with the acid left on the surface.

Copper can react, if slowly, with dilute hot acids and that is the basis for the FDA's ban on copper cookware for low pH foods. I believe, BTW, that this extends to finished beer which may not be served through brass tapping equipment unless the brass is plated to avoid contact between the beer and brass. As noted earlier if the pH of the acidified water was really 6 you should have nothing to worry about.

 

[zdegner]

So the alkalinity of your water is about 75 ppm as CaCO3?

Yes, the water in our area has an alkalinity between 73 and 83, according to the latest water report (link).

Thanks for the heads up about the FDA regulation. I looked it up and there is actually a note specific to beer brewing under the copper section (link):

The steps in beer brewing include malting, mashing, fermentation, separation of the alcoholic beverage from the mash, and rectification. During mashing, it is essential to lower the pH from its normal 5.8 in order to optimize enzymatic activity. The pH is commonly lowered to 5.1-5.2, but may be adjusted to as low as 3.2. ... The use of copper equipment during the prefermentation and fermentation steps typically result in some leaching of copper.

Because copper is an essential nutrient for yeast growth, low levels of copper are metabolized by the yeast during fermentation. However, studies have shown that copper levels above 0.2 mg/L are toxic or lethal to the yeast. In addition, copper levels as low as 3.5 mg/L have been reported to cause symptoms of copper poisoning in humans. Therefore, the levels of copper necessary for successful beer fermentation (i.e., below 0.2 mg/L) do not reach a level that would be toxic to humans.

The copper risk in beer should be quite low if this is the case, since copper levels above 0.2 mg/L would kill of the yeast and the fermentation would fail. The FDA states that copper levels below 1.3 mg/L in drinking water should be safe.

This beer seems to be fermenting quite vigorously, so it should be interesting to see what the copper levels in the wort come back as.

 

[ajdelange]

... so it should be interesting to see what the copper levels in the wort come back as.

This reminds me of a guy several years back who made wine and usually went after the sulfide with copper sulfate but ran out of that and so dangled copper wire in the vats for some time and then worried that there would be excess copper in the wine of which he sent me several bottle to be tested. The relevant reason for mentioning this is that as I recall I decided I had better digest the samples before doing the copper analysis and you should probably mention this to the guy doing your testing. The irrelevant reason is that I remember getting extremely loaded as it only took a few mL of sample for the test and that left almost a whole bottle of wine to deal with.

 

[zdegner]

The irrelevant reason is that I remember getting extremely loaded as it only took a few mL of sample for the test and that left almost a whole bottle of wine to deal with.

I'm sure he will be sampling this beer. Chemists always seem to be a lot less worried about these sort of things than everyone else, probably for good reason =)

I'll be sure to post the numbers when they come back, just in case anyone runs into a similar problem. Also, for the record, I cleaned the blue off the chiller a few days ago and it was fairly difficult to get off. Sitting it in a bucket full of slightly acidic water didnt water didn't help much, the blue didnt disolve, it took a fair bit of scrubbing.

 

[zdegner]

The results came back negative, my friend didn't detect any copper left in the wort sample. Quite possibly the yeast ate whatever was available by the time the test was done. (We don't have much copper in our water here and there are no copper pipes in the house.) We fully intend to consume this beer when it finishes in a few weeks.

This past weekend I brewed another batch (belgian wit). This time using an equivalent amount of phosphoric acid (2.5 mL) instead of sulfuric. I added the acid to the sparge water a minute or two before pulling out the coil. Even though the coil was only exposed to the acid for a few minutes, again it took on a slightly blue tinge when removed.

I might pick up some pH strips at some point and test out the mash and sparge water pH. Not too worried at this point, mostly just curious about the reaction. (Eventually I'll probably replace the coil with something stainless steel.)