Extraction - Metric vs PPG

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chungyfied

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As I am more familiar with the metric system, I have found that efficiency calculations have been strange when comparing to others using PPG method.
After some search, it appears that either Brix and gravity conversions are weird or something else is. Here's an example:

For PPG users, 46 points is used as the benchmark for 100% efficiency (1 lbs sucrose mixed in 1 gallon water yields 1.046)
However, when I convert to the metric system, this assumes 0.12 kg sucrose mixed in 1 L water (same as 1 lbs to 1 gallon) should also yield 1.046 and this is where things break down.
0.12 kg sucrose mixed in 1 L water is 10.7% Brix (0.12/1.12) and this corresponds to 1.043 in most conversion tables.

Is there something I am missing out here? This is messing up my efficiency calculations especially since spec sheets that i get use percentage extraction.
 
I haven't waded through you calcs, but just a couple things to keep in mind...

- Sucrose is actually 46.21 PPG
- It's not "1 lbs sucrose mixed in 1 gallon water." It's 1 lb of sucrose in 1 gallon of (total) solution. If you add a pound of sucrose to one gallon of water, you get a little more than 1 gallon of volume, which is not what you want as a reference when doing PPG calcs.
 
You are confusing density (specific gravity) with weight percent. Like the VikeMan says, specific gravity is weight per volume, but weight percent is weight per total weight.

If you were to mix one pound of sucrose in one gallon of water, you would end up with a solution with a SG of 1.043. To get 1.046, you would have to mix one pound of sucrose in enough water to make one gallon of solution. Same with metric, you would need to mix your 0.12 kg in enough water to make 1.0 Liters of solution to reach 1.046 SG.

Said another way, one gallon of solution with a SG of 1.046 is going to contain 1.0 pound of sugar, just like one liter of the same solution is going to contain 0.12 kg of sugar.
 
Ah silly me, that makes a lot of sense. Thanks for the help!
It seems PPG would be helpful since we typically measure volumes during a brew. I always have to convert everything into mass when using the metric system
 
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