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Home Brew Forums > Home Brewing Beer > All Grain & Partial Mash Brewing > FG a little high - is it mash temp?
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Old 01-19-2013, 02:28 PM   #1
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Default FG a little high - is it mash temp?

I brewed a Founders Breakfast Stout clone, pretty much following the recipe at http://www.homebrewtalk.com/f68/foun...-clone-139078/ except that I didn't have enough cocoa powder, so I used what cocoa powder I had and did the rest with baking nibs.

This was my first time with my new rig, a BIAB setup with a 15 gallon kettle. Brew day went pretty well, the only problem was that I didn't realize that you get significantly less grain absorption when you BIAB, and when you have 20 lbs of grain that can make a big difference . I ended up with a gallon and a half more wort than I expected, and so my OG was low (expecting 1.094, got 1.072). I suppose I should have tried to boil off some water, but I didn't have a way to measure volume in the brew kettle (something that I will change before the next brew).

So, on to my question. The recipe calls for a mash temperature of 155. I mashed in at 156, I stirred after half an hour and the temp went down to 154. I added some heat, got the mash back up to 156 and then it went back down to 154 during the second half-hour, so I hit the temperature pretty spot-on. My thermometer is calibrated and accurate. I did not have iodine to do a conversion test (something else I will probably start doing) but I very much doubt that I had any conversion problems.

I aerated the wort with an aquarium pump and an airstone, there was quite a bit of foam on top of the wort after 10 minutes. I pitched a starter of Wyeast 1056, enough cells for the 1.094 I was expecting, so I am definitely good for the 1.072 I got. I had my fermentation fridge set for 64 degrees with the probe insulated against the side of the bucket. I had bubbles after 3 hours and it was really rocking for about 3 days. My basement is cold and I didn't have a heater in the fermentation chamber, so after fermentation slowed the temperature went down to about 60. After about a week and a half I took a gravity reading and I was at 1.026, and my brewing software had me expecting a FG around 1.017. I stuck a heater in there to bring the temps up to around 68 to see if I could rouse the yeast a little. It's been there for two weeks. I took a sample this morning and it was down to 1.024.

So, my question. I know that higher mash temps = less fermentable wort, but I can't find information on how much less. 155 is on the high side, but not ridiculously so. My attenuation is sitting around 65% and 1056 should be between 73-77%. Can it all be explained by the higher mash temperature, or is there something I should be looking at for why I finished so high? It's been 3 1/2 weeks since brew day, so I doubt it just needs more time.

In any case, the sample I took tastes absolutely divine and I am planning on bottling this week. I'm not worried about the beer, just want to make sure I am not missing anything in my process.

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Old 01-19-2013, 03:21 PM   #2
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Give it a good stir/ swirl with your siphon or a spoon. I had to unstuck a batch recently by doing this, and when I did the FG dropped from 1.023 to 1.016 in about two days. That may not be your solution but it's worth a try. I also don't know how much less fermentable your wort is than if you'd mashed at a flat 154, and my gut says there's something else going on. 1.024 seems a little excessive. Kyle

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Old 01-19-2013, 03:31 PM   #3
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What is the expected FG from the recipe? The expected FG from software should be ignored as it simply calculates the average attenuation for the strain and does not consider process issues.

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Old 01-19-2013, 03:44 PM   #4
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What is the expected FG from the recipe? The expected FG from software should be ignored as it simply calculates the average attenuation for the strain and does not consider process issues.
That's part of the problem, according to the recipe my OG should have been 1.086, FG 1.023, but I missed the OG by quite a bit due to the excess water. An FG of 1.017 seems reasonable based on the recipe numbers.

I could try giving it a careful stir, but I want to avoid oxygenation. Anyone else have success with stirring?
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Old 01-19-2013, 03:51 PM   #5
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When you added heat did you stir really well while it was heating? With BIAB the wort doesn't circulate well and you could easily have had the bottom half waaaay to warm before the top even started changing temp which would give you lots of unfermentables.

Quote:
I suppose I should have tried to boil off some water, but I didn't have a way to measure volume in the brew kettle (something that I will change before the next brew).
Not even a tape measure? I use my tape to determine the amount of water in my pot before I start heating.

Quote:
My basement is cold and I didn't have a heater in the fermentation chamber, so after fermentation slowed the temperature went down to about 60.
This cold could have cause the yeast to hibernate and 68 might not be warm enough to get them going again. I bring mine up to 72 after a week at 62-64 to help them finish.
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Old 01-19-2013, 04:01 PM   #6
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Quote:
Originally Posted by RM-MN View Post
When you added heat did you stir really well while it was heating? With BIAB the wort doesn't circulate well and you could easily have had the bottom half waaaay to warm before the top even started changing temp which would give you lots of unfermentables.
I made sure to stir like crazy. First time I did a partial mash BIAB I didn't and ended up with a 15 degree temperature differential. Beer still tasted good though.


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Not even a tape measure? I use my tape to determine the amount of water in my pot before I start heating.
See, this is why I shouldn't sample so much past homebrew while brewing...

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This cold could have cause the yeast to hibernate and 68 might not be warm enough to get them going again. I bring mine up to 72 after a week at 62-64 to help them finish.
Hmmm, maybe I'll try kicking it up to 70-72. 1056 is supposed to be good down to 60.
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Old 01-19-2013, 05:12 PM   #7
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That sounds perfectly normal. My last stout had 5% oatmeal and finished at 21. You're using a lot more oats than that.

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