What does "Degrees Plato" mean?

I came to see what other people had to say, as I'm really curious about this also. All I can add is that it has to do with the level of fermentable sugars (I think), which in turn affects the level of alcohol.

 

It's a European measurement of the concentration of sugars in the wort prior to fermentation, expressed in terms of percentage (10 plato is 10% sugars). The higher percentage of sugar, the more the yeast can metabolize into alcohol:
http://en.wikipedia.org/wiki/Beer_measurement

ETA: may as well save you guys a click :

 

It's a scale for measuring the ratio of water to fermentable sugar. Most brewers in the U.S. (both home brewers and pro) use SG (Specific Gravity) instead, but it's the same idea.

 

I don't think the pros use SG, even though the labels do. I read one interview with some brewers in which one of them jokingly took a crack at another by accusing him (falsely) of using SG, the implication being that SG is for amateurs.

And here's a chart showing the nonlinear relationship between SG and Plato. http://www.brewersfriend.com/plato-to-sg-conversion-chart/

 

As a side note one could add that Balling advocated in favor of a system of taxation for beer based on the degree plato of the wort prior to fermentation, this system was implemented in 1855 throughout the Austrian Empire, which at the time included Bohemia.

Here's a table showing the volume of wort produced of a specific degree plato in 1880/81, divided by region (from what I understand the system allowed for the brewer to stay within one degree plato and still pay the same tax, i.e they could brew a beer of 10 degrees plato or 10.9 degrees and remain in the same tax bracket):

 

No problem.

You can also mentally ballpark the percentage of alcohol if you know the specific gravity- just ignore the 1 and move the decimal 2 places to the right.

That 10 degree plato beer would be 1.040 specific gravity: 4%
12 degree plato would be 1.048 specific gravity: 4.8% (close enough to 5%- remember, this isn't supposed to be exact)
etc.

 

Just to add something, and certainly something for amateur-level home brewers, 1 degree plato = 4 points of specific gravity... roughly. Keep in mind that degrees plato is the amount over 1.000 (the specific gravity of pure water).

@TongoRad is right about being able to estimate ABV by specific gravity (or degrees plato using my above trick), but the final gravity is important to keep in mind as well. A very dry beer like a bone dry saison will have a lower final gravity than something thick and sweet, like a scotch ale or an imperial stout. A saison might finish at 1.004, whereas an imperial stout at 1.024, a pretty big differential, and why you're only estimating ABV; that estimate is (I believe) based on a 'typical' final gravity of 1.010, a fairly standard finishing point for things like lagers and pale ales.

Also note that some things, such as dry meads, can actually finish below 1.000; as alcohol has a lower gravity than water, so if there's very little sugar and a lot of alcohol, it'll ultimately be 'lighter' than water.

 

Whenever I've heard brewers speak of it, I usually hear them refer to SG. However, that doesn't mean anything about what they actually do in their shop, so you could very well be right. Though I know many, I'm not a commercial brewer so I won't suggest either way.

 

Look…, the degree of "Platо" - function of dry matter (not only sugar !!!) in original wort. The taste of beer – function of extract, first of all. It’s a pity, it’s not write on the label, but easy to calculate:

10% -alcohol 4% - extract will be 4%
13%- alcohol 4% - extract will be 6%

Something like this....

 

Very interesting. No surprise 10º came out on tope in Bohemia and Moravia. Still very much the same today.

What's the source of thius chart, BTW?

 

Here:
https://archive.org/stream/jahresberichtbe02gottgoog#page/n902/mode/2up
Here's a similar table with statistics for Vienna and its surroundings, "umgebung" which I take to mean this region (which would mean it includes Schwechat) in the years 1874-1881:
https://archive.org/stream/jahresberichtbe02gottgoog#page/n900/mode/2up

 

I was looking at what you said and thinking there had to be a relatively reliable instance where an estimation would come very close. And it would appear that, assuming a consistent attenuation rate of around 75%, you could more or less move the decimal point over two places. For example:

OG 1.040 1.048 1.056 1.064 1.072
FG 1.010 1.012 1.014 1.016 1.018
%abv 3.94 4.74 5.54 6.34 7.16

I'm getting the 75% attenuation from this equation (courtesy of the White Labs site): [(OG-FG)/(OG-1)] x 100
http://www.whitelabs.com/beer/homebrew/beginners-attenuation-and-flocculation-definitions

(OG and SG can be used interchangeably here and stand for "original gravity" and "starting/specific gravity", respectively)

In other words, using the 1.040 gravity as an example, the final gravity of 1.010 was a 75% attenuation down to 1.000 from 1.040 (40 - 10 = 30... 30/40 = 75% - there's probably a better way to write that out).

I'm just figuring this out as I'm reading this thread - I used to wonder about this myself.

 

Right- that rule of thumb came from a time when there were more types of 'normal' beers available, and 75% a.a. was the assumption. When it comes to high gravity, or bone dry beers, it does get less accurate as per @Lehighace06 's post, but for the Eastern European type beers in the OP it should work just fine.

 

Well put in both cases. Of course in my homebrew I've rarely made something that wasn't bone dry and/or high starting gravity

 

I can't thank you enough for this, especially the Vienna stats. It's confirmed what I thought: that Vienna Lager got generally weaker towards the end of the 19th century. Be interesting to compare the output figures in terms of volume for Bohemia and Oberösterreich. I think they'd show a shift from the latter to the former.

I wonder what records Schwechat still has? I'd love to see their brewing logs, if any still exist.