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Home Brew Forums > Home Brewing Beer > General Beer Discussion > Plato vs. specific gravity
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Old 05-25-2012, 09:24 AM   #21
jc3375
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Originally Posted by Hegh View Post
Luckily, it's an easy conversion. Multiply the degrees Plato by 4, divide by 1000, and add 1. Or, in other words, 4 degrees plato = 1.016 SG.
over sp gr of 1.020 this equation doesn't work, here it is exactly:

{Plato/(258.6-([Plato/258.2]*227.1)}+1 = Specific gravity
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Old 05-28-2012, 12:44 PM   #22
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Don't quote me on this, but I believe in the food science or general science industry, pro-brewers are one of the only ones who use °Plato.
Professional brewers in Britain generally use specific gravity. Though even that only really caught on in the 20th century. Before that they mostly used brewer's pounds (which I prefer, personally). For weight measurements they generally use kilograms, though the volumes are in a mixture of barrels and hectolitres.

I suspect the use of Plato in the USA comes from the influence of German brewers in the 19th century.
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Old 05-28-2012, 03:07 PM   #23
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While the post showing the long list of SGX=PlatoY showed **.*Plato, no one (unless I missed it) as mentioned the decimal point in the Plato reading. Another of the many reasons that Plato is used in commercial breweries is that it gives a greater degree of accuracy than SG... not majorly so, but it does

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Old 06-01-2012, 12:26 AM   #24
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I am still confused by all this. First, is there a way to measure only the amount of sugar in wort/beer, without also measuring proteins and other materials dissolved in the beer/wort?

Second, if SG is the weight of a (sugary)liquid in relation to the weight of pure water and if degrees Plato is the percent of sugars dissolved in a liquid by weight, then why doesn't 1.1 SG = 10 Plato?

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Old 06-01-2012, 01:58 AM   #25
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Second, if SG is the weight of a (sugary)liquid in relation to the weight of pure water and if degrees Plato is the percent of sugars dissolved in a liquid by weight, then why doesn't 1.1 SG = 10 Plato?
I am not a chemist, so I could be wrong about this, but here's what I think happens. First, if I remember correctly, Plato is the weight of dissolved sugars as a fraction of the total weight of the solution, so 10 Plato would be, for example, 10 grams sugar and 90 grams water. The specific gravity, on the other hand, measures density, that is, the weight of the solution divided by its volume. When you add sugar, the volume of the solution expands to make room for the sugar molecules, so while a 10 Plato solution weighs 100/90 = 1.11 or 11 % more than the water you started with, the solution takes up more space than the original water. The SG would be 1.11 only if you could have added the sugar without the volume increasing. If the SG for a 10 Plato solution is 1.04, then the solution must have expanded to 1.11/1.04 = 1.0673, or by 6.7 %.

To put it another way, you start with 90 grams of water and add 10 grams of sugar to get a 10 Plato solution with a SG of 1.04. The solution weighs 11 % more than the water you started with, but has a volume 6.7 % greater than the original water, so the SG = 1.11/1.067 = 1.04.
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