First partial mash - OG 5 points higher?

[Hoont]

Today was my first partial mash and it was a blast! All went well though I still need to get my process down so I can get better organized. It took an hour and 40 minutes longer than extract.

Anyway, when I was done with the mash, I added some LME and my gravity was 1.034 ( I used a refractometer). Beersmith was expecting 1.033 so all is good! I boiled, hopped, cooled, transferred to a better bottle carboy and took my OG reading from what was left in the pot (.5 gallon). The OG read 1.043 and BeerSmith was estimating 1.038. I took a couple readings and all of them came back the same. What the heck? I've made this recipe many times with all extract and routinely hit 1.036 - 1.039.

I've used this refractometer for 10 -15 batches and have never had a freaky reading. I also routinely take my OG from what is left in the brew pot. Its usually one of the last things I do before I start cleaning.

As for the recipe, I mashed with 2.75 lbs maris otter, and 1 lb of specialty malts. I used 3lb pale LME.

Is taking the gravity reading from the bottom of the pot the problem? Or is something else going on here?

Thanks in advance!

[spiderwrangler]

Easy answers would be that either your mash was predicting a lower efficiency than what you got, or you boiled long enough that it was concentrated more.

[imahokie]

+1 to boiling - also could have had a boil kettle with a large amount of surface area (increased boil off)

[Hoont]

I did check the efficiency... not sure exactly how to calculate it with partial mash, but BeerSmith showed my actual mash efficiency a few % higher than what was estimated.

But the boiling is something I didn't think of... are you thinking I boiled off more than BeerSmith estimated so the final wort was more concentrated, thus giving me a significantly higher OG?

[alcaponejunior]

Mine have all been about 5 points higher than expected, albeit a small sample size. I figure that I'm just not that precise yet, despite having a very good grip on chemistry and related subjects (LOL, is that a fault here? I hope not, I have quite a few credits!).

Who cares about the exact numbers though if the beer comes out good, right? At this point I am happy because I'm drinking tasty beer that I brewed. There are various reasons why my OG has been higher, and I can't tell you what they are because I'm not measuring anything precisely enough to give a quantitative, scientifically accurate answer. My solution to this "problem" is to relax and have a home brew.

I do plan on getting Beersmith soon, btw. It's much easier than a slide-rule and a piece of paper...

[Cody]

I do plan on getting Beersmith soon, btw. It's much easier than a slide-rule and a piece of paper...

Amen to that. My last brew I used Beersmith and nailed it. But more importantly (for me), it was a much more relaxed brew session. The biggest deal for me was getting the software set up to match my brewing system. Now that I'm dialing that in, I should be even more consistent. But 5 points up or down, I don't care.

[spiderwrangler]

But the boiling is something I didn't think of... are you thinking I boiled off more than BeerSmith estimated so the final wort was more concentrated, thus giving me a significantly higher OG?

Yup, that's my thought...