Measuring SG with a scale and volumetric flask

[Francis Bonenfant]

Hello,

Let me preface by admitting that I do not like hydrometers at all. I can scarcely stand the use, calibration and cleaning of these devices, so I've been trying alternatives.

I have obtained SG values using a 100 mL volumetric flask and an electronic scale accurate to 0.01 grams. Electronic scales of this precision have become very reasonably priced, less than a hundred dollars for a small capacity (maybe 500g max) model.

The procedure is quite elementary:
You weight the flask alone (or zero in the scale with the empty flask), then add liquid to the calibration line, then weight the liquid.
Dividing the mass of the liquid in grams by the volume (0.1 L) gives the specific gravity in g/L, or by 100 mL to get the result on the SG scale which is g/mL.

With a good volumetric flask (0.1 mL precision at this size) the measurement error could be estimated as
(0.1mL/100mL + 0.01g/100g)=0.0011 or 0.11% error, with most of the error coming from the volume measurement on the flask.
On a value of say 1050 g/L this means an error of 1.155 g/L. Even if we round that to 2 g/L to be safe, it would mean that on the hydrometer scale you would have a precision of 1.050 +- 0.002. In theory this is four times less precise than a 0.0005 lab hydrometer, but as stated before I dislike a bunch of things about hydrometers, such as the risks of measurement error from a bobbing floater, foam, sticking to the sides, large meniscus or co2, which I feel are minimal or absent with a volumetric flask.

The calibration of the scale can be verified using distilled water and stock sugar/salt solutions, or a set of calibration weights, and the precision of lab glassware is rigorously tested. A precise scale is useful for a bunch of reasons in cidermaking and a volumetric flask is not too expensive.

So, my question is:
Is there is any fundamental metrological reason not to measure SG this way for cider production?

[Claude Jolicoeur]

Le samedi 30 janvier 2016 05:18:40 UTC-5, Francis Bonenfant a écrit :

I have obtained SG values using a 100 mL volumetric flask and an electronic scale accurate to 0.01 grams. Electronic scales of this precision have become very reasonably priced, less than a hundred dollars for a small capacity  (maybe 500g max) model.

Yes, I have one such scale and find it invaluable. However, although the resolution is 0.01 gram, the accuracy is +/- 0.02 gram usually with those low cost scales.

 

The procedure is quite elementary:
 You weight the flask alone (or zero in the scale with the empty flask), then add liquid to the calibration line, then weight the liquid.
Dividing the mass of the liquid in grams by the volume (0.1 L) gives the specific gravity in g/L, or by 100 mL to get the result on the SG scale which is g/mL.

Wrong. That way, you will get the volumic mass (normally denoted as RHO) of your juice or cider. Volumic mass is different from specific gravity. Also, volumic mass is a property that changes with temperature, and is most often expressed at 20C. To get the SG, you need to divide by the volumic mass of water at the same temperature as the tested sample, which is 1000 g/L at 5C, 999 g/L at 15C and 998 g/L at 20C.
Hence if you measure RHO as 1050 g/L at 20C, the SG is 1.052

 

With a good volumetric flask (0.1 mL precision at this size) the measurement error could be estimated as
(0.1mL/100mL + 0.01g/100g)=0.0011 or 0.11% error, with most of the error coming from the volume measurement on the flask.
On a value of say 1050 g/L this means an error of 1.155 g/L. Even if we round that to 2 g/L to be safe, it would mean that on the hydrometer scale you would have a precision of  1.050 +- 0.002.

Don't forget that volumetric flascs are calibrated at 20C. At some other temperature, the glass contracts or expands and the volume changes. So yes, you would get approximately the same precision as with an hydrometer if you make sure your sample is at 20C. The question is rather if this would be more rapid/easy/handy than a measurement with a good hydrometer? For my part, I don't think so, but try it!
Claude
 

[Claude Jolicoeur]

Le samedi 30 janvier 2016 05:18:40 UTC-5, Francis Bonenfant a écrit :

I have obtained SG values using a 100 mL volumetric flask and an electronic scale accurate to 0.01 grams. Electronic scales of this precision have become very reasonably priced, less than a hundred dollars for a small capacity  (maybe 500g max) model.

As a follow-up to previous post, you may try this procedure:
- keep a gallon of distilled water and your volumetric flask with your cider so these are at the same temperature as the cider.
- fill the flask with cider, measure the weight
- rinse the flask with a bit of distilled water and discard.
- fill the flask with distilled water (to exactly the same level as it was filled with cider) and measure the weight
- divide the weight of the cider by the weight of the water to get SG
- for best precision, manipulate with gloves, so your body temperature won't heat-up the flask

This would have the following advantages:
- to take care of temperature differences between the cider and 20C
- possibly better precision as it would eliminate bias in scale and flask
- give directly SG as the ratio of the weight of cider in relation to the weight of the same volume of water

Possible problem: if bubbles form on the walls of the volumetric flask from CO2 saturated cider, you might have the same problem as with the hydrometer. However, I think this could be minimised if the flask is at the same temperature as the cider.
For more infos on RHO and SG, see The New Cider Maker's Handbook, pages 157 and following...
Claude

[WV Mountaineer Jack]

You are forgetting the volume occupied by the CO2, if you degass your sample I bet you will find out it falls below the 100 ml line, seems a whole lot more trouble than just buying a real scientically calibrated hydrometer from a science supply shop. WVMJ

[Francis Bonenfant]

Yes, you are right, I confused specific gravity and volumic mass/density. My scientific education was in French, and when we refer to 'densité' it means relative density which is specific gravity, while volumic mass is often referred to as density (rho) in English.

So, it's doable to use a flask but a hydrometer is better in the long run.

I'll learn to love them I guess!

[WV Mountaineer Jack]

Think Brix instead of SG

--
--
Visit our website: http://www.ciderworkshop.com

You received this message because you are subscribed to the "Cider Workshop"  Google Group.
By joining the Cider Workshop, you agree to abide by our principles. Please see http://www.ciderworkshop.com/resources_principles.html
---
You received this message because you are subscribed to a topic in the Google Groups "Cider Workshop" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/cider-workshop/alDno5O4ydQ/unsubscribe.
To unsubscribe from this group and all its topics, send an email to cider-worksho...@googlegroups.com.
To post to this group, send an email to cider-w...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[Claude Jolicoeur]

Le dimanche 31 janvier 2016 06:18:56 UTC-5, Francis Bonenfant a écrit :

Yes, you are right, I confused specific gravity and volumic mass/density. My scientific education was in French, and when we refer to 'densité' it means relative density which is specific gravity, while volumic mass is often referred to as density (rho) in English.

I rather thought with your name that you were of French origin - from Quebec or France?
But even in French, the same confusion exists between "masse volumique" and "densité relative".
Actually, the scale that makes most sense to me is the Oechsle which is mainly used in the Germanic countries. It is the decimal part of SG times 1000: SG 1.050 is 50 degrees Oe.
And to WVMJ, I think Brix is also confusing because it leads to think one actually gets that quantity of sugar, which isn't the case.
Claude

[Francis Bonenfant]

I am from Quebec but currently enjoying a post-graduation vacation in France! Needless to say I am aggressively sampling their selection of ciders. There's nothing quite like this home.

[WV Mountaineer Jack]

Thanks Claude, I just use a good hydrometer myself. 

Are scions from your apples that you wrote about in your book available in the US?

thanks, WVMJ

--
--
Visit our website: http://www.ciderworkshop.com
 
You received this message because you are subscribed to the "Cider Workshop" Google Group.
By joining the Cider Workshop, you agree to abide by our principles. Please see http://www.ciderworkshop.com/resources_principles.html
---
You received this message because you are subscribed to a topic in the Google Groups "Cider Workshop" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/cider-workshop/alDno5O4ydQ/unsubscribe.
To unsubscribe from this group and all its topics, send an email to cider-worksho...@googlegroups.com.

To post to this group, send email to cider-w...@googlegroups.com.

[Claude Jolicoeur]

Le dimanche 31 janvier 2016 13:22:32 UTC-5, WV Mountaineer Jack a écrit :

Thanks Claude, I just use a good hydrometer myself. 

Are scions from your apples that you wrote about in your book available in the US?

Try FEDCO. They might not have them in the catalogue yet, but may nevertheless be able to provide a small number of trees.
Claude

[Dhruv Jain]

"I think Brix is also confusing because it leads to think one actually gets that quantity of sugar, which isn't the case."

Hi Claude, are you referring to the fact that once fermentation begins then a refractometer reading gets skewed due to presence of alcohol? Pre-fermentation brix does give you the quantity of sugar right? Worried since I use the refractometer quite a bit now.

Thanks in advance! 

[Claude Jolicoeur]

No...
Pre-fermentation brix gives you the sugar concentration of a pure solution of sugar in water that would have the same density (if you use an hydrometer) or the same refractive index (if you use a refractometer) than your juice.
For example, if you measure 15 Brix in a juice, you don't have 15% sugar by weight in that juice.
In fact this juice would have an SG of 1.061, a RHO of 1059 g/L, and a sugar concentration of approximately 130 g/L (I say "approximately" because this would vary from sample to sample)
So the true sugar concentration by weight in this juice would be approximately 130 / 1059, or 12.3%, quite different from the Brix reading of 15%. The difference comes from the weight of the other solids in solution in the juice that modify the density and refractive index.
This is why I think the use of Brix leads to confusion.
Claude

[Thomas Fehige]

The disadvantage of the Oechsle scale is that apparently you'd need to use values below zero for cider fermented to dryness. So, although I often "think" Oechsle, I slip into thinking SG once the hydrometer shows something like 0.998. In Oechsle, that should probably be -2, but that feels odd when everyone else says 0.998 in their books or on this list.

Trivia: Oechsle (°Oe) is commonly used in Germany, Switzerland and Luxemburg, while in Austria they use a unit called Klosterneuburger Mostwaage (°KMW), which is meant to represent the amount of sugar in grape must. 1°KMW = 4.86°Oe, thus KMW has the same limitations as Brix and is just another unit for SG. KMW is also used in Italy, where they call it degree Babo after its inventor, and in the states of the former Austria-Hungarian monarchy (Slovakia, Hungary and the states of former Yugoslavia).

Babo not only invented KMW but also had the bad luck to be the one who introduced the North American phylloxera to central Europe when he imported North American vines for his research for mildew resistant varieties.

(from wikipedia)

Cheers -- Thomas

[Claude Jolicoeur]

Le vendredi 5 février 2016 05:02:41 UTC-5, Thomas Fehige a écrit :

The disadvantage of the Oechsle scale is that apparently you'd need to use values below zero for cider fermented to dryness. So, although I often "think" Oechsle, I slip into thinking SG once the hydrometer shows something like 0.998. In Oechsle, that should probably be -2, but that feels odd when everyone else says 0.998 in their books or on this list.

Trivia: Oechsle (°Oe) is commonly used in Germany, Switzerland and Luxemburg, while in Austria they use a unit called Klosterneuburger Mostwaage (°KMW)...

I must agree the negative Oechsle degrees is a drawback for some - for my part, I never ferment to complete dryness, so doesn't apply. Also writing it "Oechsle" is quite counter intuitive for me at least - I need to write it slowly to make sure I don't make a typing error...
And as a side note, I was in the Mostviertel area of Austria last August, and the producers there did use the Oechsle scale - no one talked to me about the KMW while I was there.
Claude

[Thomas Fehige]

Glad to hear that, Claude. Those special traditional units like KMW, Brix, and, if it comes to that, pound, gallon, ton, foot etc. are, imo, interesting for historians, but otherwise, a pain. It seems, when all's said and done, the Austrian Mostviertel cidermakers you met are a bunch of pretty shrewed, up-to-date cider engineers.

Last autumn I bought a book by an Austrian cider maker, who thought it necessary to explain about the Klosterneuburger Mostwaage at some considerable length. I felt I was reading something from the eighteen-somethings (not only because of the KMW).

Cheers -- Thomas

[Claude Jolicoeur]

Le dimanche 7 février 2016 18:26:01 UTC-5, Thomas Fehige a écrit :

Last autumn I bought a book by an Austrian cider maker, who thought it necessary to explain about the Klosterneuburger Mostwaage at some considerable length. I felt I was reading something from the eighteen-somethings (not only because of the KMW).

I also brought a book back from my trip, written by Karl Stückler. Very difficult to read (for me) but it seems to be quite a good book, and fairly professional and modern. It does mention both KMW and Oe, but doesn't seem to explain on KMW in any considerable length, so I don't think this would be the book you are refering to...
And interestingly, the KMW scale does give realistic figures for true sugar content in an apple must. For example, taking a must with a SG of 1.060, the sugar content should be in average 127.8 g/L, with variations that can amount to +/- 14,4 g/L (from my book).
And for this same SG, the KMS given in the above mentioned book is 12.35 °KMW - taking this as grams per 100 ml, it would mean 123.5 g/L of sugar, quite close to my table!
Claude