Measuring gravity with a smaller sample

[Calypso]

So I generally brew 5 gallon batches, so losing 0.4% of my batch to take a sample doesn't bother me overmuch. But it got me thinking, for people that brew smaller batches, couldn't you take a smaller sample, dilute it with a liquid of known SG (say.... water), measure the SG, and then divide by the dilution % to get your actual number?

Example: I take a 20 mL sample of my beer, dilute it to 100 mL with water (20% of the final volume), measure the SG at 1.005. 0.005 / .2 = 0.025. So your actual SG is 1.025.

I realize you lose some accuracy doing this, since we generally can only get within 0.001 of the actual SG, so in this case our accuracy is going to be +/- 0.005. But for checking to see if your gravity is stable, this might be a decent alternative for small batch brewers.

 

[Oginme]

A refractometer uses only a couple of drops. You do need to adjust the reading based upon the OG and the current reading to account of the different refractive index of ethanol to get accurate results. However, if you are only looking for consistency in reading a refractometer works fine.

 

[Calypso]

Huh. I thought you couldn't use a refractometer once it had begun fermenting. I didn't know you could correct it with the OG. Well... then I guess this is for small batch brewers that don't have refractometers.

 

[Natdavis777]

There is a corrective factor that is used for refracts post fermentation, but as I understand, are not 100% accurate. I always take FG readings with a hydro, but I only take one sample (when I transfer to the keg). Maybe one could save beer by getting a narrower graduated cylinder that could still accommodate the hydro.

 

[thekraken]

I think the idea you proposed is valid. You would just have to be pretty accurate in your volume measurements. I'd be inclined to do it by weight and just set up a spreadsheet/calculator to spit out the corrected FG for me.

 

[Derek1985]

I normally account for post fermentation readings in my 1 gal batches by adding 1 cup worth of extra water.

 

[MadHomebrewer]

I do one gallon batches and use a refractometer and http://www.northernbrewer.com/learn/resources/refractometer-calculator/

A hydrometer just uses too much beer for me and I don't want to risk just dumping it back in.