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Sodium bicarb weird smell


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Hey everybody!
So I have been making a neutral vodka.  My recipe was a wheat recipe no added sugar. 
So after my first distillation stripping run I add baking soda sodium bicarbonate. This is said to clean up all the heads and tails nasties. 
However, when I am doing my spirit run towards the end of the hearts section this really nasty smell and taste starts to come through. At the beginning of the hearts it tastes great. But once I get towards the end it gets nasty smells almost like a really strong mint/industrial cleaner that has a smell added to it. And it is really strong. This has happened to me twice now. 

Has this happened to anyone else?  Does anyone have any idea what this could be or how I can fix it?

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I've used sodium bicarbonate without that happening and usually find mintiness at the start rather the end. How much did you use? Were your cuts the same size as usual? I assume these flavors weren't there when stripping or for other runs with the same recipe and ferment stats?

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  • 2 months later...

So I tried the sodium bicard treatment in some mason jars with positive results and figured what the heck - lets give it a whirl. I was working with a "hearts" cut taken from 190 proof grape spirit, but distilled on only 5 plate column so for a "hearts" cut it was headier than Vodka should be. This "hearts cut" was diluted to 100 proof, loaded about 40 gallons into the still, tossed in about 6g/l (about half a pound in all ...:blink: too much!?) and assuming it would just precipitate out when it reaches boiling - didn't expect much ethyl acetate -> ethanol conversion for sure but figured 'hey whats the worst that could happen'...and fired the still up without waiting...About 3 hours into the run I noticed the wash had turned to a dark amber (nasty dark urine?) color. Everything coming out had that minty smell and chemical taste, the entire run, start to finish. Cutting collected distillate and re-running with more heads cuts reduced it, showed it to be most strong in the heads, but didn't "fix" the problem. Not sure what to do now. Considering sending it off to a lab for GCMS to figure out what the heck is in it giving off that smell...but given that I don't know *exactly* what I'm looking for, I'll need to get some advice as to what it "might" be so I can order the right panel.

Anyone have any ideas what that smell is coming from before I do - or better yet - how the heck to get rid of it?


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Posted this two years ago over at Stilldragon.  This was the last time I experimented with baking soda for ester hydrolysis.


Ok - I wasted a lot of time and alcohol yesterday running through trials to determine what the appropriate amount of baking soda is. I didn't want to clutter up other threads this is being discussed in. The game plan is to run a set of trials with a number of different ester hydrolysis/acid neutralization approaches.

Here's what I got - Day 1 - The Sodium Bicarb Trials

First I wanted to understand the pH dynamics of sodium bicarb in a strip:

Sodium Bicarb - 2.5 grams per liter (approximately 1 tablespoon per 10 liters stripped wash) is sufficient to neutralize acids out of a typical strip and push the pH near the equivalent of a water saturated solution. Starting pH was 4.3 - by 2.5g/l sodium bicarb this was pushed to pH 8.3. Adding any more than this amount did not push the pH any higher.

Repeating the same test with a clean hearts cut (approximating a very clean strip), even less, 1 gram per liter (approximately 1 tablespoon per 25-30 liters of clean stripped wash) was sufficient to push the pH to 8.3

Then I wanted to understand what the upper limit would be, given a higher than typical acid level:

Repeated again adding 5g/liter of citric acid to a 50% ethanol solution - to simulate a very high acidity strip - probably unrealistically high, but not quite vinegar (an awful infected run perhaps). pH was 2.6. Even a small amount sodium bicarbonate was enough to turn it into alka-seltzer - with significant co2 production - you would absolutely recognize the amount of fizz. By 5 grams per liter the pH had moved up to approximately 5.1 (one tablespoon per 5 liters of wash). By 10 grams per liter the pH had moved up to 6.2 (1 tablespoon her 2.5 liters of stripped wash) . By this time there was very little citric acid flavor remaining in the sample. By 15 grams per liter the pH had moved up to 6.7 (1 tablespoon per 1.25 liters, by 20 grams per liter (1 tablespoon per 0.75 liters) the pH was up to 7.2 (and tasted very salty). Between 15 and 20 grams per liter I believe I passed the point of saturation, as I was unable to dissolve some of the sodium bicarb and it was settling at the bottom. Realistically, 1 tablespoon per 2.5l is probably the upward max, and only if your strip was awful - or distilling something with very high volatile acidity (faulted wine maybe?).

After running these tests, I realized I should have done this with acetic acid, so that I could run each of these through a distillation and organolepically assess the ethyl acetate produced during distillation. I'll try this next time, but I need a balance with a 0.1g precision so I can run smaller trials. Next time.

Next, I wanted to understand the time factor, how long did the hydrolysis reaction actually take to complete.

To understand the time factor - I distilled an "ester bomb" with the lab still. 500ml (300ml tails, 200ml hearts) - along with (50ml)acetic acid, propionic acid (10ml), lactic acid (10ml), and butyric acid (10ml), sulfuric acid to bring the pH down to about 2.4. Refluxed for one hour. Worked great - took the sickeningly sweet juicy fruit hearts cut (50%) and split it into two containers (250ml).

Began adding sodium bicarb to one sample, keeping the other sample untouched for comparison purposes. If bicarb can reduce the esters, I should be able to discern a pretty linear reduction in ester odor in the test sample, no?

Tell you what, not much of a difference, it was relatively minor. Ran all the way through 20 grams per liter, and beyond the point at which I could dissolve additional sodium bicarbonate, and the ester odor was nearly as prominent as the control sample. You could very faintly discern the butyric and acetic acid odor at the 2.5g/liter mark (1 tablespoon per 10 liters), but not much change after that. Even past saturation, but the ester odor still overwhelmed all else.

I then heated the sample, to test if I could accelerate the reaction with heat, perhaps it was just too slow. During heating I liberated a bit of vapor, which strongly smelled of volatile acids. Hmm, not what I expected. Cooled it down to see if perhaps some time under heat was sufficient to hydrolyze the esters, nope, nearly identical to before.

Gave up around 1:30am - let the samples sit overnight. Fast forward to now, roughly 9hr later - little to no change since last night. Now, it could very well be the amount of ester created was far beyond the ability to easily hydrolyze, but not sure that makes any real theoretical sense.

Decided to distill the sample this morning rather than letting it sit, I don't believe it would have done much to wait, especially since heating it made little to no difference.

Distilled into 4 equal fractions using only minor passive reflux, 3 distilled through and the final being the remaining boiler contents.


Heads fraction - still very similar overall odor, however I expected it to come through very strong as it did during the initial esterification - significantly reduced odor.

Hearts fraction, ester odor nearly nonexistent, not that I should be surprised, we know this works, I just didn't expect the very significant reduction in esters - especially since the sample going into the distillation was still very, very strong.

Tails were similar (I did start with a hearts cut) - No acidic aroma - which is typically of the tails cut during the esterification. Absolutely no ester odor.

Remaining boiler contents, shockingly free of acidic odor, as is VERY common during the esterification process. Absolutely no ester odor.

Need to run a few more trials, since what went into the final distillation test here was a sample with excess bicarb - past the point of dissolution. I'd like to try this with significantly less.

DAY 1 CONCLUSION - I strongly feel that the 1-2.5g/l amount is more than sufficient to provide for ester reduction in low wines (this is 1 tablespoon per 10 liters to 1 tablespoon per 30 liters). I do not feel that any waiting time, past the point of dissolving the bicarb in low wines, is necessary at all - the reaction was almost nonexistent cold - 9 hours no change - but clearly takes place rapidly during distillation. For the average distiller, plain old baking soda is going to be hard to beat - really, it works that well.

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I'm not an organic chemist, but the most probable source of the "minty" aroma is going to a salicylate ester (this is how most commercial mint flavors are made).  Camphor - not likely (sometimes described as minty, but more menthol or eucalyptus).

Salicylic Acid (SA) is found in both Grape and Wheat.  Looking through the literature - SA appears to sometimes be used as a preservative.

Ethyl Salicylate has a minty aroma and flavor.

Methyl Salicylate has an even stronger mint aroma and flavor than ethyl.

Other 4-methyl compounds could be the cause as well.

Why the reaction is favored, increased, etc - beyond my pay grade.

Try attempting to hydrolyze the esters (if they are salicylate esters) with NaOH during distillation in a small lab still.




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Interesting, thanks for taking the time to link + copy/paste. I'll give the NaOH a shot in a small volume on my rotary evaporator and let you know what the outcome is. Any ideas for dosage trials?

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