pre-boil gravity vs. OG issue

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storytyme

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Question for everyone out there. I've been brewing for quite awhile now. Just completed my 157th batch. The last 3 batches I've noticed a trend and am a bit baffled by it. My pre-boil gravity readings have been exact based on Beersmith. But my OG readings have been 2-3 points below what is estimated (example: 1.049 vs 1.052). So what is the deal? It will be fine as I am not worried, just a bit curious. The one thing that I've noticed is that my boil has been inconsistent (too vigorous, then too light). These have also been 10 gal batches from my usual 5 gal. Anyone with experience in this? Thank you in advance, cheers and have an amazing weekend!
 

VikeMan

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Measure the volumes (as well as the gravities) of you pre-boil wort and post-boil wort carefully. Be sure to adjust for temperature differences and account for hop absorption. Beersmith doesn't know your actual volumes unless you tell it.
 

VikeMan

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The percentage should be the same.
The volume boiled off would be about the same (assuming the heat source is adequate). The percentage boiled off would be quite a bit less (approximately half).
 

VikeMan

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Please explain using 11.25 batch vs 6.25 batch vs 2.37 batch. Is the loss percent not consistent?
The loss is roughly consistent, by volume, i.e. the amount boiled away per unit of time. But having more liquid in the kettle doesn't make more water boil away per unit of time, so the loss is not consistent as a percent.

If you could make the boiloff consistent as a percentage, you could solve global warming.
 

VikeMan

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If I use the percent loss during a 11.25 batch and and apply the same percent to a larger or smaller batch won't this result in the same volume loss?
Percentage loss is not the way to go, although I'm aware that some software asks for it that way. The onus is then on the user to figure out what the estimated percentage loss would be for any given batch size, so that they can change the input when they change batch sizes.

Let's say you've tested your boils and found that for a 5 gallon (post boil) batch, you lose 1 gallon to boil-off. So, 6 gallons pre-boil, 5 gallons post boil. 1/6 = 17% loss.

For a 10 gallon batch, you can expect to lose approximately the same 1 gallon. So, 11 gallons pre-boil, 10 gallons post boil. 1/11 = 9% loss.
 
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storytyme

storytyme

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Just to ensure I understand this is actual vs estimated hydro readings. Is this correct?

If so has the malt specs changed?
Yes. Estimated is higher then actual in this case.
 

bracconiere

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Question for everyone out there. I've been brewing for quite awhile now. Just completed my 157th batch. The last 3 batches I've noticed a trend and am a bit baffled by it. My pre-boil gravity readings have been exact based on Beersmith. But my OG readings have been 2-3 points below what is estimated (example: 1.049 vs 1.052). So what is the deal? It will be fine as I am not worried, just a bit curious. The one thing that I've noticed is that my boil has been inconsistent (too vigorous, then too light). These have also been 10 gal batches from my usual 5 gal. Anyone with experience in this? Thank you in advance, cheers and have an amazing weekend!

yeah same thing for me...i think it's the temp correction for the hydrometer because when i use a refrac for pre-boil, OG is spot on.....
 
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storytyme

storytyme

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It looks like my volume post boil is higher than what I am telling Beersmith, thus decreasing my OG. Thank you for all the replies.
 

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