OG issue

[BlindFaith]

I just brewed a 5 gal batch AG of a Founder's Breakfast Stout Clone and had no problems with a 1.065 pre-boil gravity, which according to my calculations should give me a wort of 1.083 (which is still low efficiency, but I was happy with it). Well, I just sampled it and it is reading 1.073 which doesn't make sense to me. This was 6.3 gallons pre-boil @ 1.065 and a hair under 5 gallons post-boil. I did not aerate, but there is no top-off so that shouldn't matter. Maybe it does need to be mixed. Has anyone ever had a pre-boil and post boil not match using the normal formulas? If so, what would cause this?

#14 2-row
#1 Chocolate
22 oz Flaked Oats
12 oz Roasted Barley
9 oz Black Patent
7 oz Crystal 120

Some coffee and chocolate with a low IBU hop schedule, nothing crazy.

 

[JimRausch]

If your pre-boil gravity was correct(compensate for temperature?) and your volume is correct, then your OG has to be around 1.082. I mean you couldn't have lost any sugar during the boil, just water. So, I think your 1.073 was incorrect somehow.

 

[BlindFaith]

If your pre-boil gravity was correct(compensate for temperature?) and your volume is correct, then your OG has to be around 1.082. I mean you couldn't have lost any sugar during the boil, just water. So, I think your 1.073 was incorrect somehow.

Both my refractometer and hydrometer show that 73 points. The same instruments used for the pre-boil that showed 65ish (hydrometer showed 62 and refractometer showed 65). I just checked the accuracy of my hydrometer as well and it is dead on. This is strange. I even aerated the wort and checked it again just to be sure.... same. I added chocolate, coffee, and nibs during the boil and at flameout, so I even INCREASED the sugar amount. Maybe it is wrong or the wort just isn't mixing well. It is a very heavy wort, but I don't think this is a common issue with big stouts.

 

[woozy]

Yeah, math is math and ... checks calculater ... 65*6.3/5 = 81.9. Well, something must be wrong. As you can recheck and recheck the 1.073 but you can't recheck the 1.065, I'm assuming either the 1.065 was incorrect (pre-boil not thouroughly mixed? sticky hydro? middle-aged eyes? dunno...) or your volumes are inaccurate.

sorry. sucks...
==
whoa. the 1.065 verified? Then, as unlikely as it seems, it *has* the be you pre-boil wasn't properly mixed. Or your pre and post volumes were not what you thought. I can't see anything else other than an invisible sugar eating alien jumped into your wort.

*could* your volumes be off? Could you actually have 5.6 gallons in the end rather than 5 gallons? (Or, perversely symmetric, could you have started with only 5.6 gallons rather than 6.3?)

All you can do now is record you o.g. as 1.073 and go on, I guess. Weird...

 

[BlindFaith]

It must have been an inaccurate pre-boil gravity reading, but those are usually on the low side. I am just disappointed because everything seemed to be working out for this beer, my first BIG beer. It will still be fine and it tastes wonderful. It just won't be a FBS clone unless the attenuation is off the charts, but I mashed a little higher than I wanted to start with so I probably have a few unfermentables in there. That may also be why my OG is so low. Oh well, on to the next one.

Just saw your edit woozy, my volumes are correct. My carboy is labeled for volume and I use the same measuring stick I have been using the last few months. It just had to be some kind of mix up by me on the pre-boil SG, but I was pretty happy when I saw the 65 points because I was shooting for about 84-85. It sucks, but it is what it is for now. Those gravity blues....

 

[woozy]

>>It must have been an inaccurate pre-boil gravity reading, but those are usually on the low side.

If the the wort isn't mixed and you grab a low gravity sample then logically there must also be some high gravity samples in the batch... of course those are usually on the *bottom* so one tends not to sample them.

I guess, you'll just have to chalk this one up to a fluke. Unless someone can come up with some strange sugar sucking events that could have occured.