Alcohol evaporation rate during pasteurization

[eigua]

I wonder if anyone could shed some light on how much alcohol can evaporate and how quickly at a temperature of 165f.

I'm trying to safely pasteurize rice wine. My first attempt is outlined here:
https://www.homebrewtalk.com/showpost.php?p=7577790&postcount=1277

I had to redo those bottles today, but this time I decided to go for a much simpler double boiler approach where I brought the rice wine up to 165f directly in a double boiler. I then bottled it in warm, sanitized beer bottles. The process was quite easy, but I noticed during the approach to 165f and for several minutes after, a significant amount of vapor was coming off the rice wine. I smelled the vapor and it was clearly alcoholic, giving me a noticeable burning sensation in the sinuses. It took me probably 10 minutes to bottle it after it got to 165, and after it was in the bottle I smelled it again and it didn't smell alcoholic anymore and pretty much like rice. In addition, I had 4 nearly-full beer bottles full when I started and only came out with 2 nearly-full bottles and 2 missing about an additional 2 inches each. I can't imagine I could have lost _that_ much alcohol that fast... I can't account for more than a few tsp of liquid loss otherwise. Pure ethanol has a boiling point of 173.1 f, so I wouldn't have guessed that it could boil off so quickly at 165 f.

 

[SilverZero]

There's a lot of variables going into how much alcohol evaporates at any given temperature. Ingredients, time, temperature, surface area, etc. all play into it. Also keep in mind that evaporation happens at any temperature (leave a glass of water out overnight and it will lose some volume even at room temperature). Alcohol evaporates more readily than water because of the lower intermolecular bond strength. Raising the temperature will raise the evaporation rate.

There are several studies that show just how much alcohol is left when cooking with wine and such, and the amounts vary wildly depending on the study. So, basically, it's almost impossible to judge. Any vapor you noticed was going to have a much higher proportion of alcohol to water. You clearly lost some volume, but I'm guessing there's not an easy way to know how much except maybe measuring the final gravity of the wine as it is now.

In the end, if it tastes good, no harm done.

 

[jerbrew]

Yup, measure the gravity. thats' the only way you're going to be able to determine if it had any real affect of your wine. You definitely lost some booze but you also lost some water. You're talking about a thermo problem that has a changing temperature (ramping up and cooling), changing concentration (loosing booze), and considerable mass transport factors. also remember that as liquids approach their boiling point their vapor pressures will tend to increase non-linearly. A cup of water won't evaporate very quickly at room temp but heat it up to 50C (half way between boiling and freezing) and 75C (3/4 there) you'll see significant increases in the rate of evaporation that do not increase linearly with the temp increase. In short, you'll see it evaporate more quickly as it approaches boiling.

 

[ajdelange]

I would suggest putting the wine into sterilized bottles, capping them and then Pasteurizing. In this way you will lose no alcohol.

 

[eigua]

There's a lot of variables going into how much alcohol evaporates at any given temperature. Ingredients, time, temperature, surface area, etc. all play into it. Also keep in mind that evaporation happens at any temperature (leave a glass of water out overnight and it will lose some volume even at room temperature). Alcohol evaporates more readily than water because of the lower intermolecular bond strength. Raising the temperature will raise the evaporation rate.

There are several studies that show just how much alcohol is left when cooking with wine and such, and the amounts vary wildly depending on the study. So, basically, it's almost impossible to judge. Any vapor you noticed was going to have a much higher proportion of alcohol to water. You clearly lost some volume, but I'm guessing there's not an easy way to know how much except maybe measuring the final gravity of the wine as it is now.

In the end, if it tastes good, no harm done.

Thanks for the explanation. That's what I expected. I did make the mistake of using a large bowl to double boil in, giving it a lot more surface area for evaporation. I guess the answer is: I'll never know. :/

I haven't tasted it since bottling, but the smell wasn't nearly as sake-like. I'm guessing this is going to be a pretty low alcohol rice wine. I think it was already weaker than normal sake/Chinese rice wine to start since I used enriched long grain rice instead of the typical glutenous rice. But after this pasteurization, I have a feeling it will be Bud Lite rice wine.

Yup, measure the gravity. thats' the only way you're going to be able to determine if it had any real affect of your wine. You definitely lost some booze but you also lost some water. You're talking about a thermo problem that has a changing temperature (ramping up and cooling), changing concentration (loosing booze), and considerable mass transport factors. also remember that as liquids approach their boiling point their vapor pressures will tend to increase non-linearly. A cup of water won't evaporate very quickly at room temp but heat it up to 50C (half way between boiling and freezing) and 75C (3/4 there) you'll see significant increases in the rate of evaporation that do not increase linearly with the temp increase. In short, you'll see it evaporate more quickly as it approaches boiling.

Unfortuantely, I have no SG to go off of for comparison. Making rice wine involves using solid rice which is slowly broken down into liquid sugars by amylase made by a mold while simultaneously fermented by yeast in the starter.

Your explanation makes a lot of sense and would explain why you see vapor coming off a pot long before it reaches boiling. I mistakenly assumed that with ethanol's boiling point being 173 f, I'd be fairly safe at 165 f.

I would suggest putting the wine into sterilized bottles, capping them and then Pasteurizing. In this way you will lose no alcohol.

The link I posted in my first post described my failed attempt at doing just that. Because of the dangers involved, I switched to this method. I think next time I will pasteurize in bottle, but only capped with foil with a temperature probe stuck through to tell me when I reach 165, then cap. Hopefully this method will lose less alcohol to evaporation.

 

[jerbrew]

The link I posted in my first post described my failed attempt at doing just that. Because of the dangers involved, I switched to this method. I think next time I will pasteurize in bottle, but only capped with foil with a temperature probe stuck through to tell me when I reach 165, then cap. Hopefully this method will lose less alcohol to evaporation.

I think that's a pretty good compromise between your two methods. Good luck I hope you still enjoy your booze

 

[ajdelange]

The link I posted in my first post described my failed attempt at doing just that. Because of the dangers involved, I switched to this method.

The last thing I want to do is to encourage you to do something that you are uncomfortable and this post should not be interpreted as advice to do it the way I suggested. But it is interesting to look at the pressures involved. Say the wine is 5 mol percent alcohol and consider the rest to be water. That means it is 100* 0.05*46/(0.95*18) = 13.45% ABW. Put it in a bottle and cap it at 20 °C and you will have inside 1 atm (101 kPa) pressure made up of 0.05*5.67 = 0.28 kPa vapor pressure of EtOH and 0.95*2.34 = 2.22 kPa vapor pressure of water with the remaining 98.5 kPa being that of nitrogen and oxygen (mostly). At 75 °C the pressure of the O2 and N2 is going to be up to 98.5*(273.15 + 75)/(273.15 + 20) = 116.98 (approximately as they are not ideal gasses) but the water vapor pressure will be up to 0.95*38.6 = 36.7 and the ethanol vapor pressure to 0.05*88 = 4.4 kPa. So the total is 117 + 36.7 + 4.4 = 158.1 kPa ~ 1.56 atm. That isn't very impressive. I subject beer bottles to more pressure than that when I counter pressure fill them - BUT they are behind a shatterproof plastic shield when being filled!

In reading the above keep in mind that a mixture of ethanol and water does not follow Raoult's law exactly but I don't think the deviations are likely to change the conclusions much. These are

1: The saturated vapor pressure of water isn't that great at 75 °C.
2: The saturated vapor pressure of EtOH is close to an atmosphere but the vapor pressure over a 13% ABW mixture with water isn't that much because the mole fraction is only 5%.
3: Despite 1) the major source of increased pressure in the bottle is from the increase in the vapor pressure of water.

 

[eigua]

The last thing I want to do is to encourage you to do something that you are uncomfortable and this post should not be interpreted as advice to do it the way I suggested.

This is really great info! Thank you for taking the time to do the calculations.

Perhaps I was wrong and those strange lines are not cracks then. 1.56 atm (22.92568 psi) isn't anywhere near the breaking point of even a reused bottle (58 psi according to this post).

The rice wine liquid is full of rice sediment so it's not as thin as water, but when it's in the bottle, you can easily see the lines running up the bottle against the cloudy white liquid. Once the bottle is emptied though, it's almost impossible to see anything even with bright light. I'm thinking it may be some kind of pattern in the coloring instead of a fracture line... If I had a large pot that could contain and submerge the bottles completely with a lid clamped on, I wouldn't have any issues with trying sealed bottle pasteurizing again.

 

[Chanoc]

One point to consider is that methanol which is poisonous evaporates first at a lower temperature.
This fraction is called heads in the distilling process.
There's plenty of info on the temperature this happens.
After this, ethanol boils.
Ethanol will evaporate more readily between this temperature and your selected pasteurizing temp

 

[ajdelange]

No, it doesn't evaporate first - it just has a higher vapor pressure than ethanol or water and so it leaves the liquid relatively faster than ethanol. But they leave together. If the molar ratio of a to b is ma/mb in the liquid the ratio of partial pressures of a and b in the vapor will be
ma*va/(mb*vb). = (ma/mb)*(va/vb). Thus if va > vb (which it is if a is methanol and b is ethanol) the molar ratio of methanol in the vapor will be the molar ratio in the liquid amplified by the ratio of the vapor pressures (va/vb). Thus the liquid condensed from this vapor is stronger in methanol than the original. If it is re-evaporated the vapor from it is stronger still and so on from plate to plate until an azeotropic mixture is formed (if there is one between ethanol and methanol). The fact of methanol leaving faster than ethanol or water means, of course, that its mole fraction in the liquid declines faster than those of ethanol or water. In any case we hope the original mole fraction of methanol in the wine is well below any amount we would have to worry about.

 

[Chanoc]

No, it doesn't evaporate first - it just has a higher vapor pressure than ethanol or water and so it leaves the liquid relatively faster than ethanol. But they leave together. If the molar ratio of a to b is ma/mb in the liquid the ratio of partial pressures of a and b in the vapor will be
ma*va/(mb*vb). = (ma/mb)*(va/vb). Thus if va > vb (which it is if a is methanol and b is ethanol) the molar ratio of methanol in the vapor will be the molar ratio in the liquid amplified by the ratio of the vapor pressures (va/vb). Thus the liquid condensed from this vapor is stronger in methanol than the original. If it is re-evaporated the vapor from it is stronger still and so on from plate to plate until an azeotropic mixture is formed (if there is one between ethanol and methanol). The fact of methanol leaving faster than ethanol or water means, of course, that its mole fraction in the liquid declines faster than those of ethanol or water. In any case we hope the original mole fraction of methanol in the wine is well below any amount we would have to worry about.

I am pretty sure your reply is spot on.
The idea I was trying to convey is that during this time you lose some ethanol, but you lose some of the nasty methanol.
Less of a bad stuff must be better...

 

[Chanoc]

One point to consider is that methanol which is poisonous evaporates first at a lower temperature.
This fraction is called heads in the distilling process.
There's plenty of info on the temperature this happens.
After this, ethanol boils.
Ethanol will evaporate more readily between this temperature and your selected pasteurizing temp

On my first post I meant to say METHANOL WOULD ...