Pre-Boil Gravity Didn't Make Sense

[Moonpile]

We just did our second AG and after the mash we had collectd 13 gal of wort from the following grain bill:

Amount        Item                                      Type         % or IBU      
20.00 lb      Pale Malt, Maris Otter (3.0 SRM)          Grain        89.89 %       
2.00 lb       Caramel/Crystal Malt - 10L (10.0 SRM)     Grain        8.99 %        
0.25 lb       Cara-Pils/Dextrine (2.0 SRM)              Grain        1.12 %

I was expecting a pre-boil gravity of 1.051 or so, but got 1.075 (actually 1.072 @ 82F). We were thinking we'd somehow way overshot our efficiency, but when we checked it again after the boil we got 1.058 (two points shy of our intended OG). We did not dilute in any way.

Any ideas why we would have such a wonky reading for pre-boil gravity?

The hydro sample did seem to have a lot of coagulating protiens (or something) in there. Could those have been bouying up the hydrometer? If so how can I more accurately read my pre-boil gravity?

 

[cubbies]

The hydro sample did seem to have a lot of coagulating protiens (or something) in there. Could those have been bouying up the hydrometer? If so how can I more accurately read my pre-boil gravity?

I would venture to guess this is it.

Also, are you taking a reading while it is still hot? I wouldn't use this practice. They have the "scale" where you can temperature correct, but in my experience the higher the temperature, the less accurate this gets. I would cool the wort before reading if you are not already.

Next time you take a preboil reading, let everything settle out and you will see how much is there. It has happened to me at least a couple of times that I got a bad reading because my hydro was sitting on top of a pile of gunk.

 

[ErikH]

BY my calculations 100% efficiency on that grain bill at 13 gallons would be 1.064 (1.067 adjusted for temp.), so something is definitely off. It could be the hydrometer. It could be the volume. Has the paper scale inside the hydrometer come loose? I've had that happen before.

 

[Moonpile]

We let it settle for a long time, probably most of the boil. We were using a hydrometer with thermometer in it, and the reading of 1.075 was based on 1.072 at 82F. Letting it cool (or correcting it for temp) just makes the reading higher, and this was already 20+ points more than expected.

Obviously something was wrong with this reading since after we boiled off two gallons or so we had 1.058.

 

[Moonpile]

BY my calculations 100% efficiency on that grain bill at 13 gallons would be 1.064 (1.067 adjusted for temp.), so something is definitely off. It could be the hydrometer. It could be the volume. Has the paper scale inside the hydrometer come loose? I've had that happen before.

We used the same hydrometer pre and post boil.

 

[Gabe]

Funny, I just had this happen to me. I almost adjusted my hop bill but decided to take another reading. Right back down where it should have been the first time. I attribute this false read to $hit in my hydrometer......needless to say my hydrometer got a smack down after that. P.S You run the system, don't let the system run you!

 

[ajf]

How did you collect the hydrometer sample?
If you ran some wort off from a spigot at the bottom of the kettle without thoroughly mixing the wort, then that could explain it as you would have high gravity at the bottom, and low gravity at the top.
The only other possibility that I can think of was that there was so much solid material in the sample that the hydrometer was resting on the solids rather than floating in the wort.

-a.

 

[Moonpile]

How did you collect the hydrometer sample?
If you ran some wort off from a spigot at the bottom of the kettle without thoroughly mixing the wort, then that could explain it as you would have high gravity at the bottom, and low gravity at the top.
The only other possibility that I can think of was that there was so much solid material in the sample that the hydrometer was resting on the solids rather than floating in the wort.

-a.

I think we thiefed it from the kettle after all the runnings were collected, and I'm fairly sure we stirred up first.

I'm leaning toward the explanation that there was a lot of crud in the sample and maybe the hydrometer was just sitting on it.