Pre-boil Gravity really high?!?

[drksky]

So, I'm brewing the NB Patersbier all grain kit. It's pretty simple, mash was 9lbs of Belgian 2-row at 147F and a single 3.25 gallon batch sparge. Ended up wth 7 gallons in the kettle.

The first runnings were 1.069 and end of sparge was 1.025. Mixed together, it came to a pre-boil gravity of 1.045. Now, NB says estimated FG is only 1.047 and indeed, Beersmith says pre-boil should be 1.033. Why would my pre-boil gravity be so high? I measured both with a refractometer and hydrometer (temp. corrected) and they were within 1 point.

Weird

 

[JeepDiver]

Are you sure about your volumes, and did you adjust for temp. If you haven't messured out water to check the markings on your kettle I would put my money there

 

[drksky]

I'm sure about the volumes. I've got a story pole that I use to measure the kettle volume. It is most certainly 7 gallons. I had a total of about 8.5 gallons through the mash tun. 11qts mash-in, 9 qts mash-out infusion, 13 qts sparge.

 

[BanginBanjo]

Well it's certainly possible you achieved 80+% mash efficiency, which would be better than the probably 75% or so estimated in beersmith, so that would account for a few points. You should probably have slightly more volume in your kettle too, but 7 gallons sounds about right. Hydrometers can be a little unreliable too, if they aren't lab grade. I know I've had my fair share of issues with the cheaper ones. Refractometers can be off by .002 typically too.

But it still seems like you getting a much higher pre-boil gravity than you're anticipating. You can add some water to the kettle to dilute it a bit, but be careful adding too much. I've had high pre-boil gravity's before that I diluted to around where it should have been only to end up several points low on my FG.

 

[drksky]

Just finished the boil. Ended up with 5.5 gallons of 1.052 wort, so, it's not as far off as I thought.

 

[chickypad]

Those don't add up so your first reading must have been wrong, especially since it would have given you like 95%+ efficiency.

 

[Viejo]

I'm having some really frustrating gravity/volume issues that I just don't understand. Today, I started with a pre-boil volume of 7.68 gal, and a pre-boil gravity of 1.052, both corrected to 68 degrees. As I understand things, the total gravity points in the kettle are the product of the preboil gravity (52) times the volume (7.68), or 399 points. After boiling 60 minutes, I ended up with 6.45 gal, which should have produced an OG of 61 (399 points divided by 6.45 gal). However, my OG reading was 58, 5 points shy of the calculation.

Something's out of whack, and it isn't the first time this has happened. I have carefully calibrated the water volumes in my kettle, and I always correct all readings to 68 degrees. Any idea what's going on? Assuming my water volumes are accurate, either the math is wrong or the hydrometer is off. Should I invest in a refractometer?

 

[Viejo]

Oops. Math issues: 399 / 6.45 = 62 points, and I measured 58, so I'm off by 4 points.

 

[chickypad]

What's the actual temp you are taking your readings at? I find the corrections don't seem to work so well at high temps, I get more reliable results letting the samples cool to room temp.

 

[drksky]

I measured the hydro sample at 160 at pre-boil. I only used a couple of drops for the refractometer which would have cooled to ambient pretty quickly. I didn't question the accuracy of the hydro correction since it so closely matched the refractometer.

 

[Yooper]

I measured the hydro sample at 160 at pre-boil. I only used a couple of drops for the refractometer which would have cooled to ambient pretty quickly. I didn't question the accuracy of the hydro correction since it so closely matched the refractometer.

Readings over about 90 degrees with a hydrometer are notoriously inaccurate so I'd cool the sample to under 100 degrees and then convert. However, it is pretty close to your refractometer. Did you calibrate your hydrometer with your refractometer? My correction factor is something like 1.0335 or something like that.

 

[Viejo]

I cool all my samples to close to 68 degrees, but if they're off a little I use Beersmith to make the corrections. I'm going to take some time this weekend and recalibrate all my kettle volumes and measurements (again!).

I might also invest in a more accurate hydrometer.