Hit Pre-Boil Gravity, came up short on OG

[geoffm33]

3 gallon Batch Recipe:

4.5 lbs: 2-row
.5 lbs: Crystal 20
.5 lbs: Vienna
5 oz: Capa-Pils
.75oz Cascade at 55min
.50oz Cascade at 20min
.25oz Cascade at 5min
1pkg US-05

Mashed at 150 for 1 hour and nailed the estimated pre-boil gravity of 1.039 (estimated by beersmith)

The estimated OG is 1.050 but I came in under by 9 points at 1.041. I was up against the clock for a previous commitment so I just shilled and siphoned to the fermenter. I neglected to check post boil volume until it was in the fermenter, it was about 3.25 gallons.

It was about 85° F outside with humidity at 69% and a lot warmer inside once the boil kicked in. I usually boil off 1gal per hour but that was mostly winter and spring time. This is my first brew in this type of heat/humidity. Can that extra .25 gallons account for the 9 point shortfall?

EDIT: BIAB mash volume was 4.42 gallon. Didn't record the pre-boil volume.

 

[TaylorBrewed]

what was your pre boil water volume?

 

[geoffm33]

what was your pre boil water volume?

Ooops. It was 17.7 quarts/4.42 gallons for the mash. I failed to record the post mash/pre-boil volume.

 

[TaylorBrewed]

Sorry it took so long to get back to you, I had a bunch of family stuff planned for the day. Ok my next question to you is this. How do you get your pre boil gravity? You use refractometer or hydrometer? I do BIAB as well and looking at your numbers this is what I came up with.

With out exactly knowing your pre boil volume and you saying you hit your start gravity of 1.039 I would assume this.
50 Est. Gravity Units X 3 Gallons of finished beer = 150 Total gravity units needed.

If 1.039 was correct for what beersmith projected for start Volume then you would have
39 Gravity Units X 3.85 Gallons of Pre boil wort = 150.15 Total gravity Units.

Now if you finished with 1.050 OG then you would have boiled down to 3 gallons of beer.
150.15 divided by 3 Gallons = 50 Gravity Units.

If you finished with 3.25 Gallons like you estimated then you should have finished with a OG of 1.046
150 Divided By 3.25 = 46 Gravity Units

Now for you to finish with 41 gravity Units like you said then you would have had to finish with roughly 3.65 gallons of beer. 150 Divided by 3.65 = 41 gravity Units.

So looking at this I would assume that you either have more beer then you assume. Or your pre boil readings were wrong. When you boil the sugars are not going to evaporate just the water So even if you started with a pre boil reading of .39 and had say 3.85 gallons and boiled down to say 2.5 gallons of beer the amount of sugars are still going to remain just with a higher concentrate. You final reading would be 1.060. What I do is always used a refractomter and take my reading this will let me know if I need to add Extract to account for my low reading or let me know if I need to boil down to a lower volume to get my est OG.

I hope this helps

 

[geoffm33]

Sorry it took so long to get back to you, I had a bunch of family stuff planned for the day. Ok my next question to you is this. How do you get your pre boil gravity? You use refractometer or hydrometer? I do BIAB as well and looking at your numbers this is what I came up with.

With out exactly knowing your pre boil volume and you saying you hit your start gravity of 1.039 I would assume this.
50 Est. Gravity Units X 3 Gallons of finished beer = 150 Total gravity units needed.

If 1.039 was correct for what beersmith projected for start Volume then you would have
39 Gravity Units X 3.85 Gallons of Pre boil wort = 150.15 Total gravity Units.

Now if you finished with 1.050 OG then you would have boiled down to 3 gallons of beer.
150.15 divided by 3 Gallons = 50 Gravity Units.

If you finished with 3.25 Gallons like you estimated then you should have finished with a OG of 1.046
150 Divided By 3.25 = 46 Gravity Units

Now for you to finish with 41 gravity Units like you said then you would have had to finish with roughly 3.65 gallons of beer. 150 Divided by 3.65 = 41 gravity Units.

So looking at this I would assume that you either have more beer then you assume. Or your pre boil readings were wrong. When you boil the sugars are not going to evaporate just the water So even if you started with a pre boil reading of .39 and had say 3.85 gallons and boiled down to say 2.5 gallons of beer the amount of sugars are still going to remain just with a higher concentrate. You final reading would be 1.060. What I do is always used a refractomter and take my reading this will let me know if I need to add Extract to account for my low reading or let me know if I need to boil down to a lower volume to get my est OG.

I hope this helps

Sounds about right. I have about 3.25 in the fermenter, so 3.65 post boil is absolutely within range. And my readings were via hydrometer and I just bought a refractometer yesterday so I'll be able to take readings throughout the boil.

 

[duboman]

Sounds about right. I have about 3.25 in the fermenter, so 3.65 post boil is absolutely within range. And my readings were via hydrometer and I just bought a refractometer yesterday so I'll be able to take readings throughout the boil.

Be sure you are correcting your hydrometer readings for temperature and that it is calibrated. If you are taking readings over 100F then IME, they are pretty worthless, best to be 80 or less and most ideal is the hydrometers calibrated temperature.

 

[geoffm33]

Be sure you are correcting your hydrometer readings for temperature and that it is calibrated. If you are taking readings over 100F then IME, they are pretty worthless, best to be 80 or less and most ideal is the hydrometers calibrated temperature.

Noted.

I am temp correcting them, but I see your point. Especially when dealing with imprecise volume measurements (notched handle) and high temp hydro readings the margin for error is huge.