Ok guys, I ran into an issue I can’t seem to reckon out. Hoping one of you can help.
I’m putting together a simple, consolidated info sheet on priming/bottle carbonation, and I’m running into what seems to be a significant data discrepancy.
First, I reference Palmer to find that for a 5g batch, use 3/4 cup corn sugar or 2/3 cup white sugar. From this I infer that those volumes of sugar contribute a roughly equal amount of volumes of CO2.
Second, I reference Domino Sugar’s reported data that 1c sugar weighs approximately 7oz. This makes 2/3c = 4.66 oz. Back again to Palmer, I see that he parenthetically notates the 3/4c of corn sugar as being 4oz.
From this I conclude that:
4.66 oz white sugar will provide the same level of carbonation as 4 oz corn sugar, making corn sugar more “carbonation potential dense” for lack of a better term.
This gives me an extrapolated conversion factor of .86 (e.g. if you calculate the amount of white sugar you need for your desired level of carbonation, multiplying by .86 should give you the required amount of corn sugar).
Now the rub: BrauKaiser’s spreadsheet, which is based on and agrees with other popular calculators and charts, assumes that corn sugar has LESS carbonation potential than table sugar by weight, due to the additional water content in corn sugar which must be discounted. In this model, the conversion factor seems to be about 1.1 - multiply weight of cane sugar by 1.1 to get the equivalent weight of corn sugar.
So according to Palmer’s model, 4.3 oz of white sugar = 4 oz corn sugar.
According to BrauKaiser’s model, 4.3 oz of white sugar = 4.73 oz corn sugar.
One or more of these assumptions must be incorrect. Anyone know which one(s)?
1c white sugar weighs 7 oz
1c corn sugar weighs 5.32 oz
3/4c corn sugar provides roughly the same amount of carbonation as 2/3c white sugar
4.3 oz of white sugar provides roughly the same amount of carbonation as 4.73 oz corn sugar.
Years back, I was frustrated by inconsistency when priming bottles. I started checking weight vs. volume for corn sugar. There was a huge difference, depending on how I filled the measuring cup. Kinda like weighing vs. measuring flour for bread. I reached the conclusion that volumetric measures for corn sugar were always going to be problematic and went strictly to weighing the sugar.
This is a good point. I don’t know if it’s enough to account for a whole ounce, but it’s possible. I think sifted flour is something like 2/3 the density of packed flour. Plus the resolution in a measuring cup is only 1/4 cup, can be tricky to interpolate. The only right way to measure this volumetrically is with a dry measuring cup, and then only if there is no ‘packing’ factor like flour.
We at least know that by weight corn sugar has more moisture and there requires more to achieve the same level of priming.
In HBD #5470 Fred Scheer asks about homebrew priming. I have been
priming almost all of my beers, even those that are kegged, for
several years now. I believe that the action of the live yeast on
the priming sugar helps to scavenge oxygen from the head space and
serves to retard oxidation and staling of the beer. I measure the
priming sugar by weight based on the volume of the beer and its
original fermentation temperature, using a rather complex formula
originally presented by Michael L. Hall in “Brew by the Numbers” in
the Summer 1995 issue of Zymurgy (I have incorporated the formula
into my brewing spreadsheet):
Priming sugar weight in grams = 15.195 * Volume of beer in US
gallons * (Desired carbonation level in volumes of CO2 - 3.0378 +
(0.050062 * Fermentation temperature of beer in degrees F) -
(0.00026555 * Fermentation temperature of beer in degrees F2))
The formula is based on the assumption that one molecule of glucose
is fermented by the yeast into two molecules of ethanol and two
molecules of carbon dioxide. It also assumes that the priming sugar
is completely fermentable. It includes the equilibrium volumes of
CO2 already in solution based on the original fermentation
temperature. I stress that measuring priming sugar by weight is
much more accurate than by volume. Thanks to the formula and a
digital scale accurate to the nearest 2 grams, I am able to achieve
precise levels of carbonation in my beers.
I also now use white table sugar (cane or beet) for priming rather
than corn sugar. A couple of years ago I ran out of corn sugar at a
critical time and was forced to improvise. I find no difference in
flavor as far as I can tell. To be strictly accurate, I adjust the
amount of sugar in Hall’s formula, which is calculated for corn
sugar.
After some research I found that the extract potential of corn sugar
is 1.042, based on the fact that it is approximately 9 percent
water. The corn sugar used by brewers and bakers is dextrose
monohydrate, that is, with one water molecule bound to each molecule
of glucose. The chemical weight of glucose (C6 H12 O6) is 180 grams
per mole based on the atomic weights, and for water (H2 O) it is 18
grams per mole. Therefore the weight of dextrose monohydrate is 198
(180 + 18) grams per mole, and it is 9.09 percent (18/198) water by
weight.
I confirmed this with an experiment in which I weighed 119.9 grams
of corn sugar with my laboratory balance and added distilled water
at 20 degrees C until the volume was 1 liter (measured to the
nearest 2 ml, the accuracy of the graduated cylinder I was using).
The weight and volume I used are merely scaled from the 1 pound and
1 US gallon used in calculating the extract potential. The measured
specific gravity using my reasonably accurate hydrometer was 1.042.
The extract potential of sucrose is 1.04621, used as a reference
value for gravity and alcohol calculations in brewing. Therefore I
prime with 90.9 percent (42 gravity points divided by 46.21 points),
or 91 percent in round numbers, as much white table sugar by weight
as the corn sugar calculated by the formula.
Brew on!
Bill Pierce
Cellar Door Homebrewery
Burlington, Ontario
[/quote]
Wouldn’t it be safe to assume, then, that Palmer’s 4 oz of corn sugar was “fluffy” enough to occupy 3/4 of a cup, since in order to produce both of the numbers he would have had to both weigh and measure? Running on the assumption, of course, that he neither lied nor assumed.
If so, I’m not sure that makes a material difference. Granulated white sugar doesn’t seem to be subject to the same volumetric inconsistencies that corn sugar is - I don’t see much volume being lost by “packing” cane sugar. Which means that Palmer’s 2/3 cup cane sugar was probably 4.66 oz and his 3/4 cup corn sugar was still likely 4 oz.
So ignoring the volume measure Palmer gives for corn sugar as a red herring and assuming he actually weighed it, it seems as if his data still points the opposite way. I only make this assumption because it seems so odd for him to report a weight that he himself did not weigh of a substance he knows to vary wildly in volume per ounce. The man is a chemical engineer.
Yes, that’s exactly my point. To make matters worse, I just weighed a cup of sugar and it came out to 8.2 oz, making 2/3 cup = 5.46 oz, which goes on to exceed even the “5 oz of corn sugar” standard.
Plug that into a carb calculator, and you get 2.0 volumes just from the priming sugar alone, plus another 1 or whatever is already pre
I’ve never checked the “density” of either sugar (and as several people have pointed out, that might not even be possible to do with any repeatability). On a mass basis, though, the conversion is very simple:
The molar mass of sucrose is 342.3 g, and glucose is 180.2 g. Fermentation of sucrose produces 4 moles of CO2 and glucose yields 2 mol.
2342.3/4180.2 = 0.9498
So about 95% as much cane sugar as corn sugar, to produce the same amount of CO2. Obviously this assumes the sugars are completely dry.
Well, to sum up I think I’m forced to conclude that the priming suggestions in How To Brew are inconsistent and probably wrong.
I’d still like to know how much a packed cup of corn sugar weighs. And why my table sugar seems to be heavier than Dominos.
Update: Found this info on Realbeer:
[quote]Originally posted by grizzlymike
while dextrose and DME have the same weight to volume ratios (1lb=2.4c. 1c.=6.5oz) their fermentability is not same.
[/quote]
So let’s say that 3/4 c corn sugar = 4.875 oz, not 4 oz. 4.875*.9 = 4.39. At the commonly assumed density of 1c.= 7oz for table sugar, this is about as close to being an equivalent amount as you’ll be able to measure with a measuring cup (2/3c = 4.66 oz).
4.66 oz = 1.7 additional volumes, which is probably fine for most beers. So there’s nothing really wrong with this section of the book except for Palmer’s assumption that 3/4c Dextrose = 4oz, and my assumption that the weight shown was most likely to be the accurate number. These were both incorrect.
Why my table sugar is heavy remains a mystery. I’ll try other measuring cups and other sugars and see what kind of real-world numbers I get.
I believe to achieve more consistency in the end product it would be prudent to measure the sugar by weight. It should provide roughly the same amount of sugar molecules per unit volume assuming the moisture content in the sugar is fairly consistent.
The other interesting thing is what happens when you pencil out common dry units of measurement. Assuming your measuring cup and sugar test out reasonably close to spec, you get:
1c (7oz): 2.6 vol + .9 vol (existing) = 3.5 vol. Good level for wheat beers, right?
3/4c (5.25oz): 2.0 vol + .9 vol (existing) = 2.9 vol. Light lagers, Lambics, Wheat?
2/3c (4.66oz): 1.7 vol + .9 vol (existing) = 2.6 vol. Good all-around, yes?
1/2c (3.5oz): 1.3 vol + .9 vol (existing) = 2.2 vol. The lower end, but still good all-around. Porter?
1/3c (2.3oz): .9 vol + .9 vol (existing) = 1.8 vol. English Ale, Baby!
So yeah. Weighing is much more accurate. But it’s kind of nice to know what some common measurements of white sugar would get you if you couldn’t be arsed to do the calculations and weighing and whatnot. Like I said, white sugar seems not to have the same issues as dextrose when measuring by volume, so I’d be willing to bet this would work out pretty close.
*Yeah, ok. .9 is a dumb assumption for both lagers AND wheat. I’ll have to crunch a little more and see if I can refine some rules of thumb.
