Urea - Carcinogen Precursor

[ajdelange]

I'm not sure what the source of urea would be in distilled products. Good question. Maybe it's present in what they add back to the alcohol to bring it back down to drinkable levels.

I'm certainly not sure either but apparently one concern is in the use of urea based fertilizers in the field. As has been observed, all living things that contain/metabolize protein (and by extension anything that contains nucelotides - DNA, RNA, ATP...) is going to produce some urea. As the reaction between ethanol and urea is accelerated by heat I think it is reasonable to suppose that the distillation process is responsible, at least in part, for the formation of urethane.

 

[ShootsNRoots]

The method I've been using is to add the DAP-Urea to the last 10 mins. of the boil along with the Servomyces/Wyeast Nutrient. That may or may not be a wise thing to do according this thread.

The purpose of adding to the boil would be to help dissolve the nutrient in the wort. Will the DAP-Urea dissolve in chilled wort just as well? (If it dissolves in wine must then it should dissolve in wort?)

 

[Shakybones]

The method I've been using is to add the DAP-Urea to the last 10 mins. of the boil along with the Servomyces/Wyeast Nutrient. That may or may not be a wise thing to do according this thread.

The purpose of adding to the boil would be to help dissolve the nutrient in the wort. Will the DAP-Urea dissolve in chilled wort just as well? (If it dissolves in wine must then it should dissolve in wort?)

It probably doesn't matter. The urea will dissolve just fine at fermentation temperature. There is no danger in adding it at boil, since the problem with conversion to ethyl carbamate is due to the presence of ethanol. No ethanol in boiling wort, so no problem.

 

[marinosr]

Here's my educated guess, as someone who studies microbes for a living:

It doesn't matter what form of N you add to your wort as yeast nutrient.

During the aerobic phase of rapid multiplication, the yeast are going to consume every molecule of assimilable nitrogen (including urea) for incorporation into protein and other N-containing biomolecules. This is because N is the strongly limiting nutrient (c.f. Liebig's Law of the Minimum) in a system that is replete with assimilable carbon and energy (sugars). Note that almost all of the urea will be consumed in the aerobic phase, before the yeast makes any EtOH.

It is only after the beer has attenuated and there are very few fermentable sugars left that the yeast start to catabolize en masse their proteins for energy, outstripping new protein synthesis. The decomposition of arginine, a common constituent of all proteins, produces urea, and this is the urea that reacts with EtOH to form urethane, and this only happens at the end of the fermentation. (Of course, proteins are constantly being broken down and reassembled in the cell, contributing a small background production of urea, but the cell would quickly reassimilate this N in situations where N was still a strongly limiting nutrient.)

Put simply: No matter what form of N you put in your wort, the yeast will eat it all up in the beginning, and then spit it back out as urea in the end, so don't worry about which additives you're using.

Edit: Now, limiting the AMOUNT of N you're adding will likely have an effect on how much urea you're getting out at the end, even if the form of N addition doesn't matter. But if you reduce N addition, you're going to reduce the yeast growth and fermentation activity, so I couldn't recommend that.

 

[Shakybones]

Thanks, Marinosr!

I guess we've all gotta die of something.

So you'd expect less urethane in a brew where the yeast dropped out from the high ethanol concentration but still had remaining fermentables than you would from one where they dropped out from lack of available fermentables, right?

 

[marinosr]

That's a plausible hypothesis. I still think you'd see moderate levels of urea in beers where yeast dropped out due to high alcohol in high gravity beers, though. My thinking is that, as alcohol concentrations increase, protein catabolism (which is going on all the time in active yeast cells) will outstrip protein synthesis (as making proteins is energetically expensive and the metabolism of the yeast is severly stunted by the unfavorable environmental conditions), resulting in an excess of urea. It's not so much what is limiting protein synthesis in the yeast, be it a lack of a resource (energy supplied by sugars) or unfavorable environmental conditions (high EtOH concentrations), so much as simply the fact that more proteins are being broken down than synthesized. That's just my hunch though.

 

[johnnybrew91]

As a pack a day smoker Im not worried about adding a teaspoon or two of urea/DAP in my cider/Mead batches. Your way more likely to get cancer from some weird mold in your walls or even pollution compared to something as common as urea which we consume and make in our bodies.

 

[ColumbusAmongus]

Based on my limited knowledge of chemistry, I would think that at the point when the yeast go dormant from exhausting their energy source or from reaching their ethanol threshold, any remaining urea in solution is likely to be converted over time into ethyl carbamate (time depending on temperature), due to their exposure to ethanol - now at a fairly high concentration.

Unless I am mistaken in my assumption, isn't it at least fair to say that care should be taken to limit urea addition to what can be converted by yeast into ammonium and carbonate? This rate would depend on the yeast and amount of fermentable sugar present.

All this makes my head hurt a bit. Seems simpler to just buy pure DAP next time.

This is a completely valid concern. You also have to consider that people don't follow directions and quite possibly could use too much urea and may have unpredictable amounts left. Yeast absobtion rates for urea IN YOUR vessle is a wild card as well. If you over dose with urea and have struggling yeast...I would imagine you COULD end up with higher than average levels and byproducts of urea. Temps are prob a wild card as well that will set homebrew aside from average numbers.

Keep in mind...ammonia is a carcinogen as well so pick your battles cafrefully. You don't want to jump over to a different N source thinking everythingn is fine and dandy. Maybe having left over ammonia is more of a threat than urea converting to something toxic.

Here is another random thought. Many brewers are using metal tubing off the shelf for DIY wort chillers. It is very common for metals to fail testing for toxic compounds like lead for example. Even if you are using a food grade certified metal like copper, it was most likey certified for leaching toxins ONLY from the inside of the tube AND not at hot temps. Coatings may be applied to inner surfaces to prevent leaching where outter surfaces are not if the tubing isnt intended to be submerged. Exposing the outside of tubing to hot wort could be a pretty bad practice but only testing would tell us what is going on.

In short, it is completley valid to be concerned about stuff like this. Unless there is a study specifically testing conditions home brewers are using...numbers are to be taken with a grain of salt. The only for sure thing you can do is eliminate the possible exposure by taking something out of your process.

Always keep in mind that there could be more home brewing practices that are a bigger problem so think about what has a larger impact.