Partial Mash and Off Starting Gravity Reading

I just did Austin Home Brew's Belgian White Partial Mash kit. Included:

-3# of grains
-4# of wheat DME

I used DeathBrewer's partial mash instructions from this thread: https://www.homebrewtalk.com/f39/easy-partial-mash-brewing-pics-75231/ and I did a partial boil and added top off water at the end in the carboy.

I mashed at 155 for an hour in 2 gallons of water. I sparged at 170 for 10 minutes in approx. 1 gallon of water.

After adding my top off water, the carboy shows darker coloring on the bottom and slightly lighter in the middle to the top.

I took a gravity reading off the top of the carboy after adding my top off water using a turkey baster and it came in ridiculiously low, 1.031 and the sample looked much lighter in color than the entire carboy. The kit says you should be around 1.048.

Did a search and found this thread on a similar experience: https://www.homebrewtalk.com/f37/way-off-gravity-reading-46868/

My question is, does the extract sink to the bottom then get mixed during fermentation? I am used to my old Coopers fermenter with a spigot at the bottom for taking OG readings.

It's a really common problem in the extract, partial-boil, top-off scenario. I bet the question comes up on here on a weekly if not daily basis. When the yeast become active, there will be lots of movement of the wort/beer, so it will definitely not stay stratified.

Would a post-aeration reading be more accurate?

plumbob said:

Would a post-aeration reading be more accurate?

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Generally yes, but it might depend on how you aerate (air stone vs shaking or stirring). Often it takes a lot of stirring/churning to get the sample to be uniform.

Did another PM brew with 6# of grain and 2.5# of DME (late addition @ 15 minutes left)and had the same problem with seperation. I shook the carboy with 5 gallons of wort in it and it still showed seperation.

Is there any way to get an accurate OG reading with extract brewing?

In the extract brews I have done which weren't too many we got quite accurate OG readings by taking after aeration. We would usually aerate by pouring back and forth between 2 6.5 gallon sanitized buckets about 5-6 times. Since we were pitching dry yeast packs (mostly Us-05) in our DME and LME batches, the resulting foam at the top made a perfect bed for the pitch, and they usually were very active within 3 hours. Prior to pitching the consistency of the wort seemed to be quite good after that heavier aeration. These OG readings were consistent, as we took a few to be certain.

zyx345 said:

Is there any way to get an accurate OG reading with extract brewing?

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yes, measure it before you top off then calculate to the batch volume

OG = post-boil OG * post-boil volume / full volume