Simple question about measurement

[Yannnn]

Dear community,

I have a simple yet technical question to ask you.

I brewed two different beer with the same quantity of malts but two different hops (2 smash). Here are my results :

First batch:
Pre-boil gravity: 1.046
OG: 1.060

Second batch:
Pre-boil: 1.050
OG: 1.060

In both batches, I had the same OG but not the same pre-boil measures. I noticed that I didn't swirl in both recipes. My question is : do you swirl your recipe before taking these measurements?

Thanks!

 

[Gavin C]

What were the pre-boil and post-boil volumes in the kettle of both beers?

Without knowing that a valid explanation will be hard to find. Knowing these will likey answer the question

 

[Yannnn]

I start with 1,8 gal of water and do BIAB. Pre-boil volume is probably around 1,5-1,6 gal. (approximately estimating the grain absorbtion) and post-boil is 1 gal (I brew 1 gallon batches).

Thanks

 

[tomaso]

Being two different mashes/batches that doesn't seem too strange... Slight differences do occur

 

[JGF]

Seems that the most likely explanation is how much wort evaporated off during the boil. I know this seems to be the one place we've had the least consistency in our efficiencies.

 

[agrazela]

I start with 1,8 gal of water and do BIAB. Pre-boil volume is probably around 1,5-1,6 gal. (approximately estimating the grain absorbtion) and post-boil is 1 gal (I brew 1 gallon batches).

Thanks

Well there ya go. The diff between 1.5 and 1.6 gallons (given the same amount of dissolved sugars) is more than 3 gravity points on a ~1.050 pre-boil wort.

 

[Yannnn]

Your tips are really appreciated guys! I see that slight differences can make the difference. Do you think the way I take my sample can affect the measures? (for example : if I take my OG while the cold break is "separated" from the liquid)

 

[Gavin C]

I start with 1,8 gal of water and do BIAB. Pre-boil volume is probably around 1,5-1,6 gal. (approximately estimating the grain absorbtion) and post-boil is 1 gal (I brew 1 gallon batches).

Thanks

If your preboil volume is just an approximation +/- 7-8% that would explain the variance.

Also the volume to the FV (batch size) and the end kettle volume are only the same if you're dumping the entire contents of the boil kettle into the FV. Room for different measures there perhaps.

Your tips are really appreciated guys! I see that slight differences can make the difference. Do you think the way I take my sample can affect the measures? (for example : if I take my OG while the cold break is "separated" from the liquid)

The break will settle out as the sample cools. Doesn't matter if it does not for the purposes of a gravity reading but it should settle. The more important thing is temperature of the sample.

Cool the sample to the calibration temperature of the hydrometer with the hydrometer in it as it will be at room temp and raise the sample temeprature once it goes into it. Only a small cahnge but if you're going to the trouble to chill the sample, chill the hydrometer at the same time. No major effort needed.

The correction algorithms are accurate up to a point within a narrow range of the hydrometer's calibration. Hot samples, all bets are off.