gravity points loss in brewpot

[TheZel66]

This has been happening to me over the last few brews... at first I thought it was a fluke mis-calc with the hydrometer, but now I beginning to wonder.

Before boiling, I have 352.93 gravity points. After boiling, I get 282.75. the pre-boil points represent an efficiency of 91%, while after boil represents 73%. (all temperature corrections have been applied)

Has anyone experienced this kind of loss? I've heard the browning reaction to some sugars in long boils (90 minutes) can cause a loss of points, but I can't believe it would be that much. I have the same loss with 60 minute boils as well.

 

[LarryBrewer]

Something doesn't sound right with those numbers. The pre and post boil points should be pretty close.

Please show us how you are calculating that and we'll provide input.

 

[Nosybear]

Correcting for measurement error (which shouldn't be as large as the error you're reporting), there should be no difference between the total gravity points, indicative of the amount of sugars in the wort, pre- and post-boil. It's a weird result, all right!

 

[TheZel66]

(pre boil) 22.1 qt x (1.057 - 1.000) X 1000 / 4 = 314.95 (gravity measured at 105F) corrected for temp
(post boil 14.5 qt x (1.078 - 1.000) x 1000 / 4 = 282.75 (gravity measured at 100F) corrected for temp

(oh, and by the way, the post boil included 1lb of Belgian Candi Sugar, not included in the pre-boil measurement) so the points should actually have gone up about 11 points).

My guess its the measurement of gravity at pre-boil, but I've been extra careful with that measurement, including stirring the pre-boil wort before i sample so I get average gravity reading.)

 

[LarryBrewer]

The good news is, you are computing it correctly. That leaves measurement error, or a process difference.

Here are some figures from a brew I did in March:
(pre boil) 33.1 qt x (1.041 - 1.000) X 1000 / 4 = 339
(boil complete) 25.1 qt x (1.053 - 1.000) X 1000 / 4 = 333
Close enough that measurement error is the cause of the difference.


Make sure to use the the ending kettle volume, and not the 'to the fermentor' volume. That is to say, anything left behind in the kettle (like hops absorption / trub) need to be included in the post boil volume figure.

 

[TheZel66]

The crazy thing about this is that my first brew sessions recorded on Brewer's friend, I used recipes with Maris Otter, and my pre- and post- boil gravity points are really close, similar to what you get. My last three recipes I've used Weyerman's Pilsner malt and all three have weird gravity point results like my latest. I may brew one with Maris Otter malt just for giggles to see if it's a factor.

 

[Nosybear]

Your hydrometer measurement would have to be off by 8 points for this error to occur - the amount of sugar in the pot does not change unless.... Was there a lot of hop debris and trub left in your kettle or does your system result in other liquid losses? That'll absorb some of the sugars. I once ran into that problem with an IPA. A pint of your wort lost would be just over the 8 point gravity difference (9.5 vs. 7.75).

 

[TheZel66]

I took the reading out of the brewpot after the boil and while it was cooling.. My hydrometer (I just checked) reads accurately up to 85F for sure.. the pre-boil measurement must have been bad, because that reading gives me 91% efficiency.

 

[LarryBrewer]

Readings on my first runnings have been inconsistent with blended runnings. I am still narrowing that down. Stirring does help.

I don't trust what is in the dip tube in my kettle. I run about a half pint through the ball valve, pour that back into the kettle (sanitization doesn't matter pre-boil), and then take a sample I will use.

 

[TheZel66]

i'll give it a shot next time and see if i can improve the measurement... I also broke down and got three new lab grade hydrometers from northern brewer, just in case.