Jump to content

Residual sugar after distillation?


Recommended Posts

Hello,

My understanding is that the distillation process takes out any residual sugar left from the fermentation, is this accurate?  

We double distill our rum and age it for 18 months.  We use a calibrated SNAP 50 to measure the ABV and we are off by 0.6% alc./vol when it comes to our rum, when we compare the readings with a external lab.  So we are thinking, either there is a small quantity of dissolved leftover sugar in our rum (we did not add any sugar after distillation), in which case it would explain why the SNAP 50 does not give an accurate reading as it does not work with obscurated spirits.   Another hypothesis is that the rum was not filtered enough and residual particules impact the SNAP reading.  

Your thoughts?

Chris

Link to post
Share on other sites

Sugar doesn’t distill - but barrel extractives can obscure proof.  If you have a lab balance or a scale that can weigh accurately in mg - you can try evaporating an a sample and weighing out the remaining solids.  That would answer the question.

How are you calibrating your Snap 50 before measuring?

 

Link to post
Share on other sites

Also, the snap 50 isn't always dead on, which is the reason they're not approved by the ttb for final gauging. Especially with this heat, the temp correction isn't always right. My snap seems to be off in that range during the summer when the temp of the spirits is high. Get yourself some ttb approved lab grade hydrometers and a thermometer to temp correct for yourself. These hydrometers have small ranges say 75-95 proof, 80 to 100 proof, and so on. 

  • Thumbs up 1
Link to post
Share on other sites

I second that its the SNAP 50 and not residual sugar (which will not be present in spirit after distillation) in rum or cask extractives (unless it's spending 18 months in a 10 L maple syrup barrel or similar). 

Link to post
Share on other sites

@Silk City Distillers We had fresh 95% alc./vol. alcohol and our SNAP 50 gave us a 95.01% reading, and we took measure from a few off the shelf bottles and our readings were always on target even on a summer day.  This is why we are thinking that they are some dissolved solids in our rum which would offset the SNAP.   We aged the rum in small bourbon barrel casks, nothing fancy.

Link to post
Share on other sites

There is not enough information to comment meaningfully. Was the external lab's ABV higher or lower than yours? Have you given any other samples to this lab where their readings match yours? (in other words - do you trust this lab?  if so, why?).

What analysis method did the external lab use? If they were compensating for obscuration by solids, did they report any solids levels?

If the SNAP 50 does not compensate adequately for temperature, a high temperature sample would have the opposite effect to dissolved solids. High temperature decreases the density of the sample, while dissolved solids increase the density.

Does 18 months of aging usually change the ABV?  In which direction?  Are the readings you are getting now similar to the ABV changes you have seen in the past?

Link to post
Share on other sites
On 7/31/2020 at 2:17 PM, meerkat said:

There is not enough information to comment meaningfully. Was the external lab's ABV higher or lower than yours? Have you given any other samples to this lab where their readings match yours? (in other words - do you trust this lab?  if so, why?).

What analysis method did the external lab use? If they were compensating for obscuration by solids, did they report any solids levels?

If the SNAP 50 does not compensate adequately for temperature, a high temperature sample would have the opposite effect to dissolved solids. High temperature decreases the density of the sample, while dissolved solids increase the density.

Does 18 months of aging usually change the ABV?  In which direction?  Are the readings you are getting now similar to the ABV changes you have seen in the past?

@meerkat It seems our rum contains dissolved solids, as we get a 41.97% reading with our SNAP 50 and the lab gives us a reading of 42.52%.  They use a DMA 5000M, and their method takes into account dissolved sugar and solids.  Why the rum contains dissolved solids is still an open question in my mind, but surely enough we cannot trust the SNAP 50 readings for this particular alcohol.  

Link to post
Share on other sites

Evaporate 100ml and give us the mass of the solids, we can run the numbers to see if the solids weight explains the difference in the two measures.

Otherwise it’s a guess.  An error in measurement is just as good an explanation.  Single point calibration of the Snap 50 would not expose linearity errors.

Link to post
Share on other sites

To move the apparent ABV from a true value of 42.52% down to the 41.97% that you are reading would require only 0.26 mass % of sugar/solids.  The only way to be sure of what is happening is to do as Silk City has recommended and do the evaporation test.  This will tell you the quantity of solids present. 

If your column was sufficiently overloaded to carry over that quantity of sugar you would not achieve any rectification at all, so I believe you can rule out sugar from distillation being the cause.  If there are solids present they would have to be leached out from the maturation barrels, but I don't have the experience to judge whether this is possible.  Anyway, the first step must be to determine if there are solids present, and then the next step will be to track down the source.

A word on the results from the external lab.  The top-of-the-range digital density meters sometimes incorporate a refractometer and with some fancy math the density and RI can be combined to give you the alcohol and sugar content. But this is not very accurate and is not accepted by the TTB.  Is you external lab doing it this way, or with a proper TTB approved lab distillation?

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...