Premature staling- was it copper?

[BaldApe]

I recently made a thermowell from copper tubing. I've used it in about 3 batches, and I've had a problem with a sharp, solvent-like bitterness. I had thought I had an infection problem in some of my kegs.

Most recently, an ordinary bitter than was wonderful and nutty out of the fermenter is just plain stale.

Could this be from late fermentation contact with copper? I've already made plans to replace the copper with stainless.

 

[mabrungard]

Is this in the fermenter or mash tun? If its in the fermenter, it could be adding too much copper to the beer since the beer is more acidic and therefore, corrosive. Its OK in the tun or kettle. Copper is an important micronutrient and it helps clear sulfurous compounds from the beer, but too much can be metallic tasting.

 

[brew_ny]

copper in beer is bad for you

 

[ajdelange]

I recently made a thermowell from copper tubing. I've used it in about 3 batches, and I've had a problem with a sharp, solvent-like bitterness. I had thought I had an infection problem in some of my kegs.

Solvent like flavors usually come from solvents - in particular, in beer, ethyl acetate which is quite often found in beer as there is plenty of acetate and, clearly, plenty of ethanol present in beer. Yeast usually form these if operated at high temperature which is why lagers are usually devoid of them whereas ales are not. At tolerable levels these present as the fruity flavors which are an important part of ale. Infection is another possible source.

Most recently, an ordinary bitter than was wonderful and nutty out of the fermenter is just plain stale.

Stale flavors are usually described as cardboard like or sherry like. Staling is caused by oxidation with oxygen or another oxidizing agent serving as the electron thief. Metal ions, particularly iron, can catalyze oxidation.

Could this be from late fermentation contact with copper? I've already made plans to replace the copper with stainless.

Probabably not. Copper isn't very easily dissolved in mildly acid solutions unless there is heat and acidity. You didn't say whether your thermowell was in the kettle or fermenter. In the fermenter the rate of dissolution would be lower but then the beer is in the fermenter longer than the kettle. As you know the kettle is traditionally referred to as 'the copper' and the reason for that is that kettles were usually made of copper. Modern regulations prohibit that because wort is deemed to be at high enough temperature and low enough pH that detrimental copper can leach into the wort. Certainly a thermowell will expose the beer to much less area than an entire copper kettle. Look for green rings around your irises.

If you switch to a stainless well and the flavor goes away you will have your answer.

 

[mabrungard]

According the Colin Kaminski, the state of California tested a bunch of beers from around the state for copper. This included breweries with copper kettles. Their finding: nothing! Apparently either precipitation or yeast uptake removes all copper from beer. There are no worries regarding copper unless its a late production contact where those removal processes might have effect.

 

[BaldApe]

Palmer has said that copper can catalyze staling reactions post fermentation. That would not add copper to the beer itself.

I am planning to switch to a stainless thermowell, so as they say, I guess I'll find out.

 

[ajdelange]

HBS&Y reports typical copper levels of 0.01 - 0.8 mg/L in finished beers.

Metal ions do catalyze oxidation reactions. The question as to whether there were oxidizers in your beer and, if so, whether any additional copper from the well potentiated them relative to the catalysis from copper naturally occurring in the beer (malt contains about 7 ppm).