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Old 12-01-2010, 12:01 AM   #1
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Default Low OG (Partial Mash)

I'm on my 6th or 7th batch, the first was extract, but I went to partials after that. This time I decided to something "high gravity"--AHS Winter Warmer. The make-up looks like this:

2 1/2# 2-Row
.75# Crystal 60
.5# Crystal 20
6# Pale DME

I started with a protein rest at 122F for 30 minutes, added about a gallon of boiling h20 to reach ~155F, held that for 45 minutes. Drained a gallon of my mash into my kettle, then added another gallon of boiling h20 to mash out at ~175. All in all, I had somewhere around 3-3.5 gallons pre-boil and my gravity at that point was 1.033 which (by my calculations) results in about 75-80% efficiency.

Started my boil, added my hops. Boiled 50 minutes before adding my DME (for the last 10 minutes of the boil)... Cooled, topped, pitched, etc.

OG was 1.062 at room temp, but I was shooting for 1.072. I can deal with a lower gravity beer, but for future reference I want to know what happened. Everything seems Kosher, but I probably missed something that you guys won't. Please correct me if I'm wrong or offer any suggestions.

Thanks!

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Old 12-01-2010, 01:33 AM   #2
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One thing that happened to me in my first couple of brews was undermixed wort when I checked OG. I think the stratification can lead to lighter wort at the top and therefore lower measured SG. I've had it be of by as much as 35%. Of course, stirring fixes the measurement. But it's probably too late for you to do that since you've already pitched. But if your post mash gravity was as you expected, and you topped off correctly, then you very likely hit what you expected.

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Old 12-01-2010, 01:38 AM   #3
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+1

When you do a partial boil, even after stirring the top up water and the thicker wort tend to separate a bit. If you take your sample near the top, you get a lower reading. If you take it from the bottom of the fermenter, you get a higher reading. I have my child labor brew assistant stir the crap out of mine and I take the sample while she's still stirring. Makes sure I get a good, mixed sample

I wouldn't sweat it.

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Old 12-01-2010, 02:20 AM   #4
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I'm not worried. I mean, the gravity is more than high enough to get a pretty strong alcohol content. But in my defense, I aerated that sucker for a solid 5 mins before I pitched or took a gravity reading.. The process seemed relatively flawless.. Oh well..

I'll just pop a homebrew and worry about it later!

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Old 12-01-2010, 02:37 AM   #5
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If I recall correctly, I had also aerated before taking OG and apparently that didn't even mix it well enough. I guess it would also depend on how you aerated. I tend to use an electric hand mixer at the surface. Since dissolving of DME is pretty exact - almost all DME measures 44 PPG. The only other logical explanations would be an inaccurate top-off amount, or stratification, or an inaccurate hydrometer. I found out that my hydrometer is off by 4 points.

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Old 12-01-2010, 03:15 AM   #6
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True. I can see how aerating can still leave the heavy wort on the bottom of the carboy. I just shook the hell out of it, but there's still a possibility it could have stayed down there. Plus, realistically my SG was probably 1.064 after adjusting for temp. In reality I suppose it's not that far off if it is in fact correct. In addition, I topped about a half gallon extra to make up for trub loss (which I don't usually do).. That probably lost a couple of gravity points.

At least I know what some likely culprits to the low reading could be now.

+1 to the child labor brew asst.. where can you pick one of those up? haha!

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Old 12-01-2010, 03:25 AM   #7
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Actually, your 1/2 gallon increase just about explains it all. 0.5 gallons is 10% of 5 gallons. 0.072 / 1.10 = 0.065. So, you are within a point.

I also try to top off with 0.5 gallons to offset trub loss. I like to get 54 bottles per batch.

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Old 12-01-2010, 04:18 AM   #8
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hmmm.. I just never would have thought that a half gallon would give you that much of a drop in gravity, but when you put it into perspective (10%) it's really significant.. Good deal.

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Old 12-01-2010, 04:23 AM   #9
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+1

Raising the volume will certainly do that. I always adjust my recipes to make 5.5 gallons from the start.

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Old 12-01-2010, 05:13 PM   #10
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So.. With an increased volume and presumably diluted solution, should I expect my final gravity to be lower than expected also?

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