Original Gravity Conundrum

[nickofosho]

I just finished brewing an imperial milk stout this weekend and am getting some very perplexing gravity readings. The pre-boil/pot-mash gravity came in at 1.084 (which was pretty close to the BeerSmith estimate) and now the post-boil/OG gravity is 1.082! I had a 2gal boil off starting at 7.5 gal boiling down to 5.5 gal. I'm 99.9% sure I read the pre-boil gravity correctly and 100% sure I'm reading the post-boil/OG correctly.

The mash didn't go perfectly... Mashed in and temp started at 162° and took a bit of stirring to get it down to the desired 156°, which took about 20-30min. The mash was also pretty thick because I was maxing out my 10gal mash tun and had no room for rice hulls, so the runnings where super slow. I batch sparged.

Here is the recipe:

10 lbs Pale Malt (2 Row) UK
5 lbs Pale Malt, Maris Otter
3 lbs Caramel/Crystal Malt - 40L
3 lbs Oats, Flaked (1.0 SRM)
1.75 lbs Carafa Special II
1.5 lbs Barley, Flaked
12.0 oz Milk Sugar (Lactose)
0.75 oz Nugget [13.00 %] - Boil 60.0 min
1.00 oz Perle [9.30 %] - Boil 30.0 min
0.75 oz Nugget [13.00 %] - Boil 30.0 min
1.00 oz Goldings, East Kent [4.70 %] - Boil 15.0 min
2.0 pkg Irish Ale (Wyeast Labs #1084) [124.21 ml] (3L two step starter)

Any help/input is greatly appreciated.

Thanks!

 

[day_trippr]

7.5 gallon pre-boil @ 1.084
5.5 gallon post-boil @ 1.082

There's no escaping it. Unless you replaced wort with water, at least one of those measurements was erroneous, and any jury in the land would finger that post-boil reading.

I'm calculating a 7.5g pre-boil of 1.087 and in turn a 5.5 post-boil of 1.118 (that's a big fella right there )

Cheers!

 

[doug293cz]

7.5 gallon pre-boil @ 1.084
5.5 gallon post-boil @ 1.082

There's no escaping it. Unless you replaced wort with water, at least one of those measurements was erroneous, True this!

and any jury in the land would finger that post-boil reading. Not this juror. I'm more inclined to believe the pre-boil SG is in error because the OP didn't mix the first runnings and sparged wort well enough, and sampled from a zone richer in first runnings.

I'm calculating a 7.5g pre-boil of 1.087 and in turn a 5.5 post-boil of 1.118 (that's a big fella right there )

Cheers!

Brew on

 

[nickofosho]

Yeah, that's the same numbers I got via a boil off calc, but I'm sure I read my hydrometer right. Maybe it is broken... I've got a refractometer in the mail. Hopefully it will give me the proper reading.

 

[nickofosho]

Brew on

That makes a lot of sense too. The second running entered the kettle rather slowing on top of the first runnings, so they may not have mixed together well. That means my efficiency was crap though...

 

[John Eberly]

What was the temperature of your post-boil sample? It could easily have been warm enough to deflate your measurement. Hydrometers are calibrated at only one temp - usually 60 F. Maybe you know this...

I would suggest that you get comfortable with the hydrometer though, it's more reliable than the refractometers I've seen - you get better resolution with the hydrometer in my experience.

 

[nickofosho]

What was the temperature of your post-boil sample? It could easily have been warm enough to deflate your measurement. Hydrometers are calibrated at only one temp - usually 60 F. Maybe you know this...

I would suggest that you get comfortable with the hydrometer though, it's more reliable than the refractometers I've seen - you get better resolution with the hydrometer in my experience.

I thought about that too, but I corrected for temp. I've been using a hydrometer for the past 30 beers, with no issues..

 

[PurpleJeepXJ]

Are you using a hydrometer that is calibrated to 155*?

 

[nickofosho]

Are you using a hydrometer that is calibrated to 155*?

That's a good question. I believe it is calibrated to 68.

 

[PurpleJeepXJ]

I think there is your problem. I have never used a hydrometer calibrated in the 60s on 150* wort. I am sure someone has before. I would actually be interested to see how a 150s hydrometer reads in 60* water and vice versa... I may try this when I get home

 

[Cavpilot2000]

Yeah, you have to compensate for temperature. At 155 degrees, your SG reading will be vastly different from what it would be at 68.

Here is a tool (there are many others too) to plug your numbers in with temps at which the readings were taken. It will give you an adjusted SG reading.
http://www.brewersfriend.com/hydrometer-temp/