Pre-Boil Gravity

SSBrew - 728
Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum

Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
U

UdonPete

Well-Known Member
Joined
Aug 13, 2021
Messages
166
Reaction score
66
Location
Thailand
Do you take the Pre-Boil Gravity reading after the 60 min mash or after the 75C 10min Mash Out ?

Thank you
 
I have a higher mash efficiency than my recipes require, which works to my advantage. I lauter more than I need into multiple pots (drives my wife nuts) and then I get the readings of each. Then I blend them to get the pre-boil gravity exactly where I want it since my boil off rate is always the same. The left over wort is adjusted to 1040 with either water or DME and pressure canned in quart jars for future starters. It sounds more complicated than it actually is and has resulted in me being more satisfied with my beers.

Do you know how to calculate your gravity units for adjusting? If not, I'd be happy to help!
 
Removed and drained, for sure.

Pre-boil gravity should cover whatever total volume was captured from the mash - including sparge if performed. The only question imo is whether adjuncts such as sugars or extracts are included. For my recipes, I do not include anything other than what was extracted from the mash to make the mash efficiency that much more evident as I don't add such ingredients until just before flame-out which is a rather late point to know if the mash worked well :)

Cheers!
 
I don't normally take pre-boil SG's but when I do it depends on why I'm checking. Sometimes I'm wanting to know more about what my mash efficiency was and other times it's more for OG concerns after the boil.

If you are going to adjust the boil amounts with top off water before starting the boil, then you need to figure out whether your SG you are getting is more for checking your mash/sparge and other things pre-boil, or just to reference something after the boil such as OG.

If using a hydrometer, let the wort cool, not just for temperature difference inaccuracy, but because many hydrometers have wax holding the weights and other stuff inside the glass and you really don't want to melt that and make a mess if you happen to turn the hydrometer upside down.
 
Everyone here has had some kick ass input, I really hope something resonated with you that is going to bring your brewing to the next level!
 
UdonPete said:
Do you take the Pre-Boil Gravity reading after the 60 min mash or after the 75C 10min Mash Out ?
Click to expand...

I agree with the others...Pre-Boil Gravity is the gravity of the full amount of wort just before the boil starts. Note that BeerSmith has a Post-Mash Gravity and a Pre-Boil Gravity. The difference being that Pre-Boil contains sugars added into the boil. I suspect other software have similar measures.

I am a BIAB brewer. I will normally take a quick volume and gravity reading after I have pulled the bag and it has drained for a few minutes. At this point I can still adjust if I am a little high or low on volume or gravity (say stop draining if I am at my targets, squeeze the bag if I need more volume or gravity points, etc.). I will then usually take the "official" pre-boil reading just before the boil starts. If needed, I could adjust the length or vigor of my boil based on my pre-boil gravity and volume.

A refractometer helps a lot with this. For many years I only took a gravity reading when I was transferring chilled wort into the fermenter. That works as well, and I still always ended up with beer in the end!
 
CascadesBrewer said:
I agree with the others...Pre-Boil Gravity is the gravity of the full amount of wort just before the boil starts. Note that BeerSmith has a Post-Mash Gravity and a Pre-Boil Gravity. The difference being that Pre-Boil contains sugars added into the boil. I suspect other software have similar measures.

I am a BIAB brewer. I will normally take a quick volume and gravity reading after I have pulled the bag and it has drained for a few minutes. At this point I can still adjust if I am a little high or low on volume or gravity (say stop draining if I am at my targets, squeeze the bag if I need more volume or gravity points, etc.). I will then usually take the "official" pre-boil reading just before the boil starts. If needed, I could adjust the length or vigor of my boil based on my pre-boil gravity and volume.

A refractometer helps a lot with this. For many years I only took a gravity reading when I was transferring chilled wort into the fermenter. That works as well, and I still always ended up with beer in the end!
Click to expand...
 
pvtpublic said:
I have a higher mash efficiency than my recipes require, which works to my advantage. I lauter more than I need into multiple pots (drives my wife nuts) and then I get the readings of each. Then I blend them to get the pre-boil gravity exactly where I want it since my boil off rate is always the same. The left over wort is adjusted to 1040 with either water or DME and pressure canned in quart jars for future starters. It sounds more complicated than it actually is and has resulted in me being more satisfied with my beers.
Click to expand...
This is so ridiculously simple but clever to take the leftover, adjust to 1040, and can it. Wish I thought of that myself :)

@UdonPete - Everybody else is right. If you are BIAB then the pre-boil gravity is what you have after you pull the bag and drain or squeeze. It's the final volume you have directly before the boil. @CascadesBrewer gave some good advice above as well. I see you read that. You can always adjust by topping up with some water or adjusting the boil.

If you're dialing in your system then also keep in mind the grain absorption rate. That's going to affect your pre-boil volume which, in turn, is going to affect your pre-boil gravity. Some of the estimates out there are pretty off for grain absorption but there are a few useful HBT threads that take polls of BIAB users and should get you to a good initial starting number for absorption rate. For example, I squeeze pretty hard and have a rate of about .08 gal/lb. Note your pre-mash and post-mash volumes for a few brews and figure out your grain absorption rate. That constant will drive you mash water volume and get you to the point where you aren't always adjusting your pre-boil too much to get your numbers right. If you're BIAB then you really might not need that mash out either. I have never seen a convincing argument for doing a mash out, especially for BIAB, but maybe I am missing something there.

Good luck! You'll dial in to your setup with some care and attention and things always get much smoother and more consistent.
 
eliastheodosis said:
This is so ridiculously simple but clever to take the leftover, adjust to 1040, and can it. Wish I thought of that myself :)

@UdonPete - Everybody else is right. If you are BIAB then the pre-boil gravity is what you have after you pull the bag and drain or squeeze. It's the final volume you have directly before the boil. @CascadesBrewer gave some good advice above as well. I see you read that. You can always adjust by topping up with some water or adjusting the boil.

If you're dialing in your system then also keep in mind the grain absorption rate. That's going to affect your pre-boil volume which, in turn, is going to affect your pre-boil gravity. Some of the estimates out there are pretty off for grain absorption but there are a few useful HBT threads that take polls of BIAB users and should get you to a good initial starting number for absorption rate. For example, I squeeze pretty hard and have a rate of about .08 gal/lb. Note your pre-mash and post-mash volumes for a few brews and figure out your grain absorption rate. That constant will drive you mash water volume and get you to the point where you aren't always adjusting your pre-boil too much to get your numbers right. If you're BIAB then you really might not need that mash out either. I have never seen a convincing argument for doing a mash out, especially for BIAB, but maybe I am missing something there.

Good luck! You'll dial in to your setup with some care and attention and things always get much smoother and more consistent.
Click to expand...
Agree my rate is also very low (I squeeze hard) but interesting to read about your theory on mash-outs, thanks
 
kevin58 said:
I take pre boil gravity readings when all the wort is in the boil kettle before the boil begins.
Click to expand...
^^^This^^^

We take a gravity reading when the boil kettle is full, prior to starting the boil.

There is not always a huge difference in the readings, however.

Pre-boil gravity: 1.052 / Brix: 12.6

OG: 1.054 / Brix: 13.0
 
Oleson M.D. said:
^^^This^^^

We take a gravity reading when the boil kettle is full, prior to starting the boil.

There is not always a huge difference in the readings, however.

Pre-boil gravity: 1.052 / Brix: 12.6

OG: 1.054 / Brix: 13.0
Click to expand...
Only 2 points difference after boiling? This does not sound very likely.
 
kevin58 said:
I take pre boil gravity readings when all the wort is in the boil kettle before the boil begins.
Click to expand...
This- I take mine post sparge once I'm at full preboil.

rburrelli said:
Only 2 points difference after boiling? This does not sound very likely.
Click to expand...
Surely it depends how long you boil for, and on your evaporation rate? I've frequently only seen a 3-4 point change between preboil and OG when I'm doing a 30m boil, particularly with lower gravity beers.
 
With that low of a gravity change, are you covering your kettle during boil?
 
No. 75 minute boil, very, very rigorous. I was surprised at the small difference.

It went from 13 gallons to 10.5 gallons during the boil.
 
The math doesn't add up at all. Gravity points don't change unless your kettle is leaking. 1054 OG in 10.5 gallons means you have 567 gravity points in your wort, divide that by your starting volume means you should have had a preboil of ~1043.
Or the other way around, 1052 in preboil = 676 gravity points, it should be 1064 OG. This one seems a lot more plausible. Perhaps you misread 64 for 54?
 
The readings, both pre and post boil, were accomplished with a refractometer.

The line in the sight gauge was well defined, and easy to read. I double checked, just to be sure.
 
Oleson M.D. said:
The readings, both pre and post boil, were accomplished with a refractometer.

The line in the sight gauge was well defined, and easy to read. I double checked, just to be sure.
Click to expand...
You are defying the laws of physics. Not possible.
 

Similar threads

refect
How far will the flavor from lactic acid carry over?
Replies
9
Views
604
mabrungard
mabrungard
refect
Measuring Kettle PH
Replies
25
Views
1K
Indian_villager
I
Vladimir Kim
Low OG
Replies
6
Views
588
IslandLizard
IslandLizard
F
IPL?
Replies
5
Views
802
Cheshire Cat
Cheshire Cat
PashMaddle
Brew day #2 is done.
Replies
22
Views
1K
lumpher
lumpher

Latest posts

Back
Top