Second Partial Mash - aerating & OG question

Thanks in advance for anyone who takes the time to read this and provides some feedback. I have a question relating to aerating on a partial boil batch & its effect on OG.

Little background first; i just finished brewing my 5th batch, the last two of which were partial mash coming up with my own recipes. First three brews were kit beers put together by my LHBS. The kits beers came with LME, the two partial mash brews i did with DME.

Of the three kit beers i made i only aerated one, the other two i just topped up with tap water. In all cases, OG was right around what the kit predicted. Ive read that aerating isnt critical when adding tap water because the water contains o2 & the splashing off adding the water helps add oxygen as well.

On my first partial mash, i used 5 lbs pale malt & 3 lbs DME, boiled, cooled, dumped into fermentor, added top off water as usual. OG was really low, around 1.020, so i chalked it up to me screwing up the mash somehow, i hadnt taken a gravity reading after the mash so i had no idea if i got any conversion. In any event, i pitched the yeast, boiled another 3 lbs of DME a couple days later & added to the fermenting beer. The beer turned out just fine, quite enjoyable actually, produced a couple of mild hangovers though.

On my second partial mash i dialed back the grain a little to 2lbs pale, 1 lb crystal, 1/2 lb roasted barley. After mashing i took a gravity reading which was about 1.020 in 9 quarts of water @ around 150 degrees. Started my boil, added 4 lbs dme. Again, cooled, dumped into fermentor & added top off water from the tap(no aerating), again extremely low gravity reading, 1.022 this time. Based on my initial gravity reading after the mash (1.020 + 15 points for temperature adjustment) im figuring i got about 15.5 gravity points per gallon from the mash (35/2.25gallons), adding another 176 points for the 4 lbs DME(44 points ea lb) gets me to a total of 207 gravity points, divided by final batch size of 5 gallons, my OG should have been around 1.041. Assuming all my math is correct & that i know i got conversion from the mash the only conclusion i could come to was that the wort did not mix thoroughly with the top off water, resulting in my low gravity.

Would it really be off by that much though?

Could something else in my process have contributed to the low gravity?

This made me wonder if i had actually gotten conversion on that first partial mash i did, and by adding that extra 3 lbs of DME ended up with a beer in the 7-8% alcohol range, explaining the mild hangovers i had from drinking 5-6 full pints.

thanks for any help.

First of all, you can't trust calculations on hydrometer readings beyond say 80 degrees.

You are adding top off water. Are you sure you are mixing that water with the wort well enough? The sugary, more dense stuff will want to stay on the bottom.

I don't see you mentioning Sparging the grains. You might have left some sugars behind if you didn't.

How did you mash?

BendBrewer said:

First of all, you can't trust calculations on hydrometer readings beyond say 80 degrees.
Why cant hydrometer readings be trusted above 80 degrees? Whats the point of the temperature adjustment values provided with the hydrometer if there is no accuracy to them?

You are adding top off water. Are you sure you are mixing that water with the wort well enough? The sugary, more dense stuff will want to stay on the bottom.
I guess this is my main question, would not mixing/aerating the whole batch be enough to throw the gravity reading off by 20 or so points?And if so, was it just dumb luck that the first few kit beers i made mixed well just adding top off water? Besides the partial mash the only difference between those brews and the latest ones were they used LME instead of DME(not sure if this matters) and i topped off with water from a pitcher, whereas the last two, with my new deeper sink i was able to get the bucket right under the faucet, either way the water came from the same source.

I don't see you mentioning Sparging the grains. You might have left some sugars behind if you didn't.
I did sparge, on the first partial mash the grains were mashed, drained then sparged in a separate pot of water @ 150 for about 20-30 min. sparge water was then added to mash & boiled. The second partail mash i mashed and then drained the grains in a collander & decided to try just rinsing them slowly with 150 degree water. At this point while i want to make certain i am getting some conversion, i am not all tht interested in necessarily maximizing my efficiency, there will be plenty of time for that as i continue to gain expereience.

How did you mash?
The first one i tried mashing on the stovetop for an hour in my brewpot with a grain bag. I treid to keep the mash right around 155 but had some difficulties regulating temperature. Because I was concerened about the bag singing on the bottom of the pot, I ended up keeping it pretty taught, this created large temp differences between the middle of the mash and outer edges of the pot, i think it also prevented the water from really mixing well enough with the grains. I contributed my low OG on this batch to this crappy setup, specifically i thought maybe i got the water to hot & shut down conversion. The second batch went much better, heated the water up to about 165-170 in the brewpot, took it off the stove, dropped in the grain bag with grains, stirred well and put it in the oven for an hour which had been warmed up to around 150. The mash was right @ 150 after the hour.

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See replies in blue above, thanks for any continued help.

1. The higher the temperature the less accurate your hydrometer gets even with temperature correction. Just cool your wort down and then measure, no big deal.

2. This is what I think the issue is here. If you don't mix the wort you are definitely not going to get accurate readings. You HAVE to mix.

3. You should be MASHING between 148-158 and SPARGING over 180.

wasnt aware that the temp correction was that inaccurate, no prob chilling the wort down in such a small quantity next time.

I guess i just figred if the top off water was going to add the necessary oxygen for the yeast why bother mixing and inroducing potential infoection from the mixing aparatus. That said; if it means me having no clue what the hell im making, ill risk the infection from here on out.

Thanks for the heads up on the sparge temp, onward and upward. looking forward to giving this another try in a few weeks, keeping my fingers crossed that this last one just wasnt mixed well enough and that it doesnt come out ridiculously light/watery from a lack fermentables..... in any event it seems to be fermenting nicely.

What part of buffalo are you from btw? I used to live there about 10 years ago.

North buffalo, right by UB south campus. Moved here from rochester about 8 years ago.

I used to live in Hamburg, actually moved to Victor outside of Rochester after that, before coming to Atlanta.

That's cool, quite a change of lifestyle/climate I'm sure. No more lagering in your cold ass basement during the winter months though

Haha thats for sure, although I was not brewing back then...not old enough. I'm lucky to even HAVE a basement down here in GA.

Update:

I recently re-brewed the beer previously mentioned in this thread with very little change in procedure or ingredients. I did sparge @ a higher temp & played with amounts of specialty grains and extract types. This time I did cool and test the wort after mashing, i dont have the numbers in front of me but the gravity was as it should have been or at least close to it. This time however, i DID thoroughly mix the wort after adding top off water and low and behold OG was about 1.044, success!

So...... to summarize for any newbies like myself, if you're doing partial boils and adding top off water & you want accurate gravity readings MIX YOUR WORT before sampling.

now its time to get a mash & lauter tun together and start moving towards AG.....