Inconsistent hydrometer readings

[russeII]

This past Friday I brewed an all grain hefeweizen and I'm trying to figure out my original gravity. I took a sample from the kettle after it was cooled down and measured 1.054. This was higher then I was expecting (expecting 1.047)but more water had evaporated then expected so the higher gravity made sense.

So I was left in a position to decide whether I wanted to dilute or not to get to my expected volume/gravity. I wanted to make extra sure my reading was correct so I pulled a sample from the primary and read 1.047. Sounds good, but remember I had a lower volume then expected. I was expecting 1.047 at 4.5 gallons and I had 4.1 gallons in the primary after straining off about a half cup of trub/break.

Would the straining have made a difference? Could it be extra gas from the transfer?

Oh, and if I use math to figure out what the gravity should be based on my pre-boil volume/reading I get ~1.051 which is straight in the middle.

Summary:
Pre-boil volume 5.88 gal
Pre-Boil Gravity: 1.036
Post boil volume Kettle: ~4.17 gallons
Post-boil gravity Kettle: 1.054
Post boil volume into primary (minus removed trub):~ 4.10 gallons
Post-Boil Gravity from Primary: 1.047

All readings adjusted to 60 degrees from readings taken around 75F (I know, not as accurate, but still, it's a 7 point swing).

Any ideas?

 

[duboman]

Well, not really sure:

1.054 at 75 corrected to 60=1.056
1.047 at 75 corrected to 60 = 1.049

This also assumes your thermometer is properly calibrated as well as your hydrometer. If there was some trub in the hydrometer cylinder that could also have affected your readings as the hydrometer may not have been floating properly.

If you did in fact boil off more than expected then yes, your readings should be a bit higher than expected as well as you condensed the wort.

 

[JimRausch]

Hydrometers are not supposed to be affected by floaters or sediment, only dissolved solids. So my guess is one of 3 things: 1.incorrect reading(if you're like me you need reading glasses and a bright backround). 2. incorrect temperature. 3. inaccurate hydrometer(check it in distilled H2O at 60*), or as you suggested 4. gasses not given enough time to degass. Did you hit her with O2 before the bucket reading?

 

[stpug]

Hydrometers are affected by dissolved solids, as mentioned above. If you by chance pulled a cloudy sample from the boil kettle, and pulled a clear sample from your primary, AND a large portion of the cloudiness was unconverted starch then it _could_ explain the drastically different readings. That's a hard one to nail down exactly.

My suggestion would be to pull a sample and refrigerate until everything settles (24 hours maybe). Then carefully pour off into your hydro tube; allow to warm up to 60F; take another reading. I would trust this reading the most.

Alternatively, refractometers are not affected by unconverted starch so you could take a direct reading using one regardless of cloudiness.

 

[russeII]

Yeah I think I'm going to get a refractometer sooner then later. I use a wine thief and I find it near impossible to get a good reading without the hydrometer touching the sides. I feel I got a better "spin" on the hydrometer with the kettle sample, but still.

The readings were already adjusted to 60 degrees by the way.

I didn't add oxygen through an external source but I did let it drain from the kettle over a nice drop and it was a very hard pour. Definitely got lots of foam.

I didn't mention but it really doesn't matter to me too much what the reading is, it's not going off to competition or anything. I'm mainly trying to get accurate readings so that I can better estimate my efficiency.