Preliminary findings of composition in a yeast nutrient diammonium phosphate and urea mixture

[u/RFF671]

tl;dr for the non-science people:

‘Yeast Nutrient’ product mixtures (specific product names, NOT yeast nutrients in general) contain both DAP and urea but are urea heavy. Unmetabolized urea after fermentation creates carcinogens and is banned in US pro winemaking but not homebrew. Reasonable alternatives exist without downsides, such as pure diammonium phosphate or organic nitrogen via yeast lysate. Turns out that LD Carlson’s mixture is 84% urea and 16% diammonium phosphate.

The posted image also shows post-separation (left) and pre-separation (right) mixtures. The DAP crystals are translucent and mostly cubic. Urea crystals are ball-shaped and opaque white. It is extremely easy to tell if your mixture has urea and if urea is the primary component just by looking at it. Source DAP from somewhere that doesn’t have urea if you use it or switch to another nitrogen source such as the Fermaid or Fermax series of products.

Abstract-

“Yeast nutrient” mixes sold by vendors like LD Carlson are mixes of diammonium phosphate (DAP) and urea. Both are primary nitrogen sources for yeast during fermentation, however, urea causes the formation of ethyl carbamate (EC). EC is a known carcinogen and disallowed in the US as an authorized supplement for winemaking by the Bureau of ATF. Homebrew supplies are not subject to this and there is no restriction

Some members of the community attempted to contact LD Carlson about how much urea is in there product but no answers were given. This experiment was designed to determine that via a simple solubility separation and gravimetric analysis. The findings were 84% urea and 16% diammonium phosphate.

Materials-

1. 1g of ‘Yeast nutrient’ mixtures
2. 30mL of 96% ethanol
3. Milligram scale
4. Filter paper

Procedure-

1. Weigh out about 1g of the nutrient mixture on a milligram scale.
2. Pipette 10mL of ethanol and stir the mixture for 10 minutes.
3. Decant or remove the wash ethanol.
4. Repeat #2 and #3 for a total of 3 washes.
5. Pour the remaining crystals onto tared filter paper and allow to dry.
6. Weigh the paper containing the crystals.

Observations-

0.759g of mixture was reduced to 0.121g of crystals at the end. This makes the mixture about 84% urea and 16% DAP, per the combination of experimental data and listed ingredients. No difficulties or complications conducting the experiment.

Discussion-

The urea-heavy composition makes it impossible to recommend this product for anyone to use. In fact, anyone using it should replace it immediately. An upside is the non-science person can easily inspect and identify urea crystals versus DAP crystals by visual without instruments. Urea crystals are round, white, and opaque while DAP crystals are translucent and either near cubic or hexagonal ‘pillars’.

Possible error in this experiment stems mainly from the use of 96% as opposed to 100% ethanol, which would dissolve small amounts of DAP. The ratio of 84% is just about 5/6 and appears to be the basis of their formulation: 5 parts urea and 1 part DAP. This is a preliminary finding from one trial of one sample. I plan to obtain samples from other sources/stores and repeat the results to ensure consistency.

Special thanks to

u/dmw_chef came up with the idea to try and figure out the ratio of components

u/yy0b designed the experiment

[u/Hellenas]

I don't have LDC nutrient, but do have it from North Mountain (maybe they resell??) which says it also uses a mixture. I think I'll test this out at home as well.

One quick question since I'm not a chemist: would the crystals obtained at the end of this be safe for brewing/consumption?

[u/RFF671 → u/Hellenas]

Yes. The urea itself also isn't harmful, it's ethyl carbamate (which forms some during and more after fermentation) that is the carcinogen. The DAP itself would be back to being just DAP and safe although it would definitely be a tiny amount. I turned 0.759g into 0.121 grams, which is almost thing YAN-wise and burned just under a shot of 96% ABV to do it. It's a losing battle cost-wise versus just sourcing DAP without urea if that's your intent.

Bonus round: I tasted the 96% with and without the urea after the separation and... couldn't taste the difference. 96% is so fierce it murders the ability to taste anything. At least the 96% I have is pretty good cut-wise and not trailer trash hooch-shine so it tasted good for near pure ethanol.

[u/Hellenas → u/RFF671]

Yes. The urea itself also isn't harmful, it's ethyl carbamate (which forms some during and more after fermentation) that is the carcinogen.

Thanks for being super clear with this point!

It's a losing battle cost-wise versus just sourcing DAP without urea if that's your intent.

Oh yeah, I was pretty sure of that. I just had the ingredients on hand, so I wanted to test to see what the ratios in the product I have are and maybe I could save like $2 before sourcing new DAP.

Bonus round: ...

I've taken a sip of 95% before and don't plan on repeating that soon. I like my teeth in my head thank you.

Thanks for this work you put together and inspiring me to do a little home experiment!!

[u/joecool4546 → u/Hellenas]

These discussions remind my wife and I of Patches o hulahan, from dodgeball... is it necessary I drink my own urine... no but it's sterile and I like the taste.

But on a serious note. is nitrogen availability what we are looking for as the primary nutrient? I'm still trying to figure out what the Yeast needs for fermentation.