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Diluting wort to obtain high gravity reading on Big W hydrometer - is there a formula?

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Piggy Smalls

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Hi all

I have just gotten back from LHBS as I am planning on brewing a Belgian Golden Strong Ale tomorrow morning. I forgot to get a new hydrometer and the only one I have is one of the Big W ones that only goes to 1.040.

I am expecting the original gravity to be around 1.070 and am wondering if I am able to dilute my OG sample and then use a conversion calculation to work out the true OG. For example, if I dilute the sample with 50% water and get a reading of 1.035 would this indicate a true OG of 1.070 for the undiluted portion of the sample or is it more complex than that?

If anyone is able to help before I start my brew tomorrow it would be greatly appreciated.

For anyone interested - I am hoping to brew something like Duvel using German Pilsner, a little bit of Carapils, a LOT of table sugar. Hopped with Styrian Goldings (I could only get NZ grown) and Saaz. I am using the Mangrove Jack's Belgian Ale yeast - never used MJ yeast but I am hoping that the 22% of sugar making up the fermentables will help me get down to 1.005 or lower.

Cheers
Piggy
 

Sidney Harbour-Bridge

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Your theory is correct, if you dilute with an equal amount of water you could double the SG reading to obtain the correct value. That said, there is lots of opportunity for error and the result will be approximate at best.

As far as I know, the yeast and fermentation temperatures are what distinguish Belgian ales.
 

MHB

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He's right.
Would get you close if you are careful, if you want to get a better result, run a couple of hundred mL into a bottle (plastic) and freeze it until you get the chance to buy a better hydrometer.
 

Piggy Smalls

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Thanks SHB. I’m not too worried about exact OG, as long as I can check I’m in the ballpark I should be pretty happy.

Thanks for the suggestion on freezing the wort MHB - it will be good to know for sure what ABV it comes out at before I start drinking it considering I’m aiming for 8.5%.
 

MHB

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If you want an equation it's (or one of them) called the standard dilution equation, very useful for all sorts of jobs like diluting wort, mixing up chemicals... even the strike water equation is just an expansion of this equation.
C1V1+C2V2=C3V3
Where C is a condition. Temperature, SG, mg/L...
Where V is a Quantity. Could be a Volume, Mass, Number of Moles...
All the units are the same
And V1+V2=V3

In your case if the OG is unknown and you measured accurately 2 of 100mL samples, one of water one of wort and mixed them together, clearly you would have 200mL of sample if it had an SG of as above say 1.035.
There is one problem SG is called non unitary in that it is just a comparison to the density of water in this case you can get away with it but you have to be very careful using SG in equations. Often better to convert to Plato.
from what you know
SG(unknown)*C1(100mL) + 1.000(SG water)*C2(100mL) = 1.035 (SG measured sample)*200(mL mixed sample)
Solve what you can
100*OG +100 = 207
Rearrange the equation
OG=(207-100)/100
OG=1.070

Mark
 

Piggy Smalls

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That’s awesome. Thanks Mark!

Just as an update - I diluted 50/50 and got a reading of 1.036 so I’m pretty confident I hit 1.070 or slightly higher.
Pitched two packs of Mangrove Jacks M41 into the wort on Sunday arvo and it’s down to 1.028 already. Got some serious sulphur aromas coming out of the fermentation chamber. I’m very much looking forward to when this one is done.
 

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