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The Big Ester Hydrolysis Thread

edited December 2015 in General

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.

NOW WE ARE TALKING

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.

Going to try this again with Sodium Hydroxide - across a number of different pH ranges - for the heck of it (I think it will be more effective, and I can control for much smaller additions using the liquid) - and again in a fermented wash, without causing a Schweitzer's reagent reaction (which is likely due to overuse of nutrient and adding WAY TOO MUCH alkalinity/baking soda).

Comments

  • edited December 2015

    The other reason to go through all this headache - is to understand what levels of addition provide for minor reductions in ester profile without complete elimination - for example - trying to make a light ester rum - without losing flavor by having to distill at a higher proof, or completely losing the ester profile all together, or keeping some character in a vodka, etc etc etc. The reactions are not all-or-none, they are a continuum.

  • Thanks for saving us all a lot of time, the 8.3 number right in the beginning, I will use that number tomorrow as a marker when I add washing soda... great stuff!

  • edited December 2015

    Fantastic work Grim. The traditional lore said that using bicarbonate that it would take a week or so for the effect to take place at a tablespoon per 10 litres, but using carbonate it would be overnight/instant and need significantly less (teaspoon per 10 litres).

    StillDragon Australia & New Zealand - Your StillDragon® Distributor for Australia & New Zealand

  • @grim ^:)^

  • I'm not entirely sure that 8.3 is the end-all, it's just the peak pH with Sodium Bicarbonate. You may not need to go that far, but will need to run more trials at set intervals to know - ph 3, 4, 5, 6, 7, 8, 9. Need to redistill another larger ester bomb, and go from there.

  • edited December 2015

    Acid/base chemistry is funny stuff. It is based on a logrithmic scale, so by definition it is not linear. Each whole number increment is ten times higher or lower than the previous one.

    pH 8.3 is a magic number in the carbonate system. Note which species is dominant at pH 8.3:

    image

    image.jpg
    450 x 288 - 32K

    I'm more like I am now than I was before.

  • So HCO3 breaks down into CO3 when heated. Could that have something to do with it working better in the still? I doubt it but perhaps carbonate is a better choice than bicarbonate?

    Also, if the goal is 8.3 then a simple titration with phenolphthalein might be an easy way forward. You'll get to your target regardless of the starting pH with no need to test.
    The only question is would it have unwanted side effects?

    It be interesting to see where this goes.

  • Not sure what I did wrong but the WORST thing I have done with a neutral low wines was to add sodium carbonate. Smelled great before doing the spirit run but foamed to the moon and back then tasted like shit. Had to re-distill it 2 more times to make it usable.

  • Wasn't it just baked soap powder?
    What did it actually taste like?
    Not sure what happened but I wouldn't write it off too quickly.

  • edited December 2015

    Sounds like your washing soda had added surfactants.

    I would never trust washing soda, period. Back in my reef aquarium days guys would try to use washing soda to raise alkalinity and someone would inevitably nuke their tank by buying a box with undisclosed ingredients. It wasn't guys picking up the wrong box either.

    If you baked bicarbonate, who knows, but that shouldn't happen.

  • If 8.3 is the ballpark number, carbonate is going to get you there with less being required.

    I don't know about working better, unless an even higher pH than bicarbonate can get you to yields an even better result.

    I think less is more is the right approach here, but will test it out as soon as I get some more naoh delivered.

  • It was Arm & Hammer 100% pure baking soda that I converted into sodium carb by heating it. Now I just add the bi-carb and let it sit for a few days. MUCH better.

  • Would be great to know what pH you brought the wash to before distilling. Did all of your sodium carbonate dissolve? It had to be ballpark 11.

  • No, like a dumbass I didn't check the pH. All of the carb was dissolved but maybe I ran it too quickly (2 hours). I had read that bi-carb needs to sit for a few days but carb didn't. At least for my use, I now know different. I have some neutral low wines that have been sitting with bi-carb for abut 2 weeks. Not sure if I will have time to run it for another week or two. Has almost no smell but it didn't right after I added the bi-carb anyway. I will check the pH on this one.

  • The carbonate i used to use (soda ash) came from a water treatment plant and worked very well.

    StillDragon Australia & New Zealand - Your StillDragon® Distributor for Australia & New Zealand

  • @FloridaCracker said: I have some neutral low wines that have been sitting with bi-carb for abut 2 weeks. Not sure if I will have time to run it for another week or two. Has almost no smell but it didn't right after I added the bi-carb anyway. I will check the pH on this one.

    Checked the pH on this one right before I ran it and it was 8.1. Very noticeable when heads stopped and I pulled the plug when the abv dropped from 95 to 93 (not corrected for temp) so I never detected any tails. First impressions before airing are that it will be fairly clean after just 2 runs. Also, I collected slower than usual; about 4 liters per hour. Bicarb seems to be the ticket for me from now on when doing neutrals.

  • I have been using PH+ pool chemicals, it claims it is 100% sodium carbonate. I haven't checked ph, but it has truly cleaned up my vodka on the 2nd distillation. The heads are almost non existent ( I do pretty tight cuts on stripping run ) and it will run odorless sweet vodka for hours, when the tails do hit it is obvious.

  • edited December 2015

    Not 100% relevant to this thread but interesting article:

    Artisan Spirit: Winter 2015-16 by Artisan Spirit Magazine

  • ~200L of 50% low wines and previous Nuetrals at 6.5ph, added maybe a cup of carbonate (Arm&Hammer pure washing soda), went to 11.3ph.... ooopsie... lots of sediment after leaving overnight too, drained it back out of the boiler, cleaned, and will rack clear stuff back in tomorrow...

  • Just an FYI, you would not want to titrate your whole wash batch with phenolphthalein. This pH indicator has been used by many juvenile chemist in pastries and drinks as it is a strong laxative. You would not want this in your wash.

  • Who drinks their wash/low wines?

  • I don't titrate my wash with phenolphthalein but I can guarantee that it will give you the shits if you drink it.

  • Had a terrible Mud doctor that was giving me the shits on the rig when i was working as a derrickman thought id return the favour by putting 1 drop in his cup of coffee. Didn't see him for 3 days, he wasn't well at all. I felt bad after, was talking to a medic months later he said I was lucky he didn't end up in hospital it can really fuck you up if you ingest even a little bit. Lucky he never drank the whole cup just a few sips before it was cold. I now never mess with anyones food or drink lesson learnt. Don't need that on my conscience.

  • I also ran Bicarb in my last neutral strip left it a week but still had bicarb on bottom of Demi figured I added too much (3Tablespoons in 54L)run went fine bit light on due to shit ferment but when I cleaned up and emptied the boiler I had a thick layer of white/grey sediment on bottom of boiler I figured it was calcium from water used to dilute wash. Would it have been the acetate etc precipitating out once heated?? The smell in the Demi changed almost straight away when I added bicarb to it.

  • @Johnboy said: I also ran Bicarb in my last neutral strip left it a week but still had bicarb on bottom of Demi figured I added too much

    Happened to me once because I just put it in the small opening and it kinda fell through. Now I take a liter or so out and mix it thoroughly THEN pour it into the carboy. No more sediment.

  • Cool I'll do the same then

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