Hit pre-boil gravity/volume, but OG 9 points lower and volume lower than expected

[mtnagel]

Still pretty new to all grain brewing. I've been doing BIAB for about 10 months. Thought I was getting a handle on things, but I'm not sure how this happened.

I hit my pre-boil gravity and volume, but I had lower than expected volume going into my fermentor, so wouldn't the OG being higher because it's more concentrated? But my OG was 9 points lower than expected.

The only thing I can think is that I did a hopstand with 3.5 oz of hops, so I'm sure some of the loss of volume came with them sucking up some of the wort and I can see that it would take up the sugars too, so there wouldn't be a concentration effect with that, but I'd think Beersmith would take that into account and I can't imagine it would be all that much volume. And I really haven't seen that happen with my other hoppy beers.

If you need more specific numbers and processes, let me know, but I'm thinking I'm missing something obvious.

 

[crocks86]

How did you measure your gravity? I've definitely had this problem using a refractometer. Over time figured out it's good to do a few measures each time I want to check the gravity because they can be a little wonky since it's using such a small sample. But temperature adjustment can probably play a big part when using a hydrometer.

 

[mtnagel]

Yes it was a refractometer, but I sampled twice. I've had issues when the sample wasn't stirred properly, but this was after pouring into the fermenting bucket from the pot, so I assume it was homogeneous. I guess I could see it being measurement error. I'm not really concerned with it, as I'm actually glad it's a little lower in ABV. Instead of 9%, it will be 7.7% - fine by me. But I still want to know what I did wrong so I can correct it for future batches.

 

[mtnagel]

Anyone else have any ideas on this? I'd love to get to the bottom of this.