I am confused. When is "original Gravity" measured to determine mash tun efficiency? - Home Brew Forums
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01-07-2011, 10:59 AM   #1
jetmac
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 I am confused. When is "original Gravity" measured to determine mash tun efficiency?

I thought OG was post-boil but before pitching. But after reading How to Brew, chapt 12.5 it says this:

But, when it comes to the efficiency of the mash and lauter, we want to think in terms of the pre-boil gravity.

Palmer's Short Stout (target OG = 1.050)
Malts
6.5 lbs. of 2 Row
0.5 lb. of Chocolate Malt
0.5 lb. of Crystal 60
0.5 lb. of Dextrin Malt
0.5 lb. of Roast Barley
(8.5 lbs. total)

For our example batch, we will assume that 8.5 pounds of malt was mashed to produce 6 gallons of wort that yielded a gravity of 1.038. The brewer's total sugar extraction for this batch would be 6 gallons multiplied by 38 points/gallon = 230 points. Dividing the total points by the pounds of malt gives us our mash extraction in points/pound e.g. 230/8.5 = 27 ppg. This value is good, if not great; 30 ppg is basically what everyone shoots for. Comparing these numbers to lager malt's 37 ppg maximum gives us a good approximation of our mash efficiency: 27/37 = 73%, while 30/37 = 81%.

01-07-2011, 11:34 AM   #2
StarCityBrewMaster
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I believe either can be used for OG but as far as efficiency is concerned I use my preboil wort to get that number. That's the best way to get a reading and efficiency with only the sugars from your grain being present.

Here is a link to a Brewhouse efficiency calculator if you don't already have one:
http://www.brewersfriend.com/brewhouse-efficiency/

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01-07-2011, 11:37 AM   #3
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The reason you want to use pre-boil for the MLT efficiency is because after the boil, you've evaporated off some water and will have concentrated the wort. This will raise the gravity of the wort. If you were to use the post-boil numbers, you'd get really good efficiencies, but they wouldn't be accurate as to what you are able to extract from the grains.
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01-07-2011, 08:29 PM   #4
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Yeah OG and pre-boil gravity are two different numbers and both are important. Pre-boil is very good to know because it lets you know your efficiency, and whether or not you need to add extract or water to the wort in order to come out post-boil at your desired OG. The OG, in turn, is useful for telling you the ABV of your finished beer.

01-07-2011, 10:44 PM   #5
malkore
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its also probably confusing because there is 'mash efficiency' which is the pre-boil and brewhouse efficiency, which is the post-boil gravity after you evaporate some liquid.

mash efficiency is good to know cuz the better the efficiency, the less you spend on grain.

the OG post boil is what you'd use for all your ABV and final gravity calculations
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01-07-2011, 11:09 PM   #6
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Quote:
 Originally Posted by Docjowles Yeah OG and pre-boil gravity are two different numbers and both are important. Pre-boil is very good to know because it lets you know your efficiency, and whether or not you need to add extract or water to the wort in order to come out post-boil at your desired OG. The OG, in turn, is useful for telling you the ABV of your finished beer.
Ditto this! Or at least what Doc said is my take as well. Efficiency isn't a big concern to me, once I get a feel for a setup. If I have to toss more grain next time to get the OG to near target I'll do that, rather than fret over what part of my process if making me fall short a few points. There are anal brewers who take delight in every little detail, and ghetto/trash brewers like myself. We all make pretty excellent beer, most all the time.

The only reason I even look at my OG is to make sure I got enough fermentables to make at least a decent ABV of 5+, preferably 6+. If I get a sweet wort that has the potential of 6-9, and I ferment it down to completion.... It will be, what it will be, and I am fine with that.

Less math, brew on! is my philosophy.

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01-08-2011, 04:17 PM   #7
jetmac
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Quote:
 Originally Posted by malkore its also probably confusing because there is 'mash efficiency' which is the pre-boil and brewhouse efficiency, which is the post-boil gravity after you evaporate some liquid. mash efficiency is good to know cuz the better the efficiency, the less you spend on grain. the OG post boil is what you'd use for all your ABV and final gravity calculations
This is still a little confusing when using the BeerSmith and ProMash refractometer tools.

When entering the information into the refractometer tools is the OG number supposed to be from wort pre-boil or after boil?

If I enter the pre-boil gravity reading I took with my hydrometer of 1.049 and my first fermenting refractometer reading of 9.23 brix, the results of the refratometer tools line up with the fermenting hydrometer reading I took at the same time. >1.028<. But if I enter the post boil gravity reading I took with my hydrometer of 1.062 the results in the refractometer tools are different. >1.021< That would mean my hydrometer reading during fermentation is wrong because it says my gravity is 1.028. Then would that mean I couldn't trust any of the hydrometer readings.

Which OG number should I use and what would cause my hydrometer to read incorrectly (assuming it is)? Maybe too much CO2 floating the hydrometer?

02-02-2011, 04:30 PM   #8
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do you take OG after the top off? I know before pictching, but theres that extra step of the top off :-\ thanks

11-25-2013, 03:02 AM   #9
rubenr3
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Quote:
 Originally Posted by RogueGoose85 do you take OG after the top off? I know before pictching, but theres that extra step of the top off :-\ thanks
Any answer to this question? Very curious.

11-25-2013, 03:07 AM   #10
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Quote:
 Originally Posted by rubenr3 Any answer to this question? Very curious.
if you top off yes after the top off but make sure it's mixed well

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