# Can wort layering significantly affect OG reading?

A few days ago I brewed a 5-gallon recipe with the following fermentables:

• 8 oz Crystal 20
• 8 oz Crystal 40
• One 3.3 lb can Briess Munich LME
• 2.5 lb Light LME

Beer Calculus predicts an OG of 1.046.

For the first time in years, I got distracted for a moment and there was a boil-over. This is an annoying complication to my question (which is coming below). I don't believe too much was lost during the boil-over. I know I started with about 1.5 gallons of water when I mashed the grains. After removing the (waterlogged) grains and sparging with maybe a quart of water, I added the syrups. After the boil-over, I noted that I still had about 1.5 gallons in the pot. Now, having cleaned up the mess, I'd say about a pint of wort was lost to my stove top. When I consider the water that would have been removed with the grains, I feel like these numbers add up, but I'll let the experts weigh in on that. If I'm right about losing a pint when there were 2 gallons total, that would reduce Beer Calculus's OG estimate to about 1.043

So I finished my brewing, and topped off the carboy to 5 gallons. After I pitched the yeast, I took a gravity reading: 1.030. That seems incredibly low! At first, I told myself that the combination of losing some concentrated wort during the boil-over and a low efficiency from the mashing might explain it. So I told myself whatever happens will happen with this batch, and I went to bed.

But this morning I had another memory/realization. My girlfriend and I both noticed a ring about 1/3 of the way up in the carboy after the brewing. It was a ring of particulate inside the wort. I thought that was neat - there was a little meteorogical system in the carboy. Liquid of a heavier density had settled to the bottom and the particulate was floating on top of it. Possibly relevant - I used Irish moss in this batch (1/2 tsp for 10 min) which I do not normally use.

So I wonder: could my low OG reading be (in significant part) because I sampled from the top, where the less dense liquid was? Or is this just wishful thinking? I've never before seen the layering I saw with this batch. Does anyone else see that in their recipes?

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