Lower FG than expected

So I did my first AG brew this past Sunday, everything went smoothly and had no big surprises or problems. I'm making an amber ale, and my recipe is as follows:

Phecke's Amber Ale
10-B American Amber Ale
Date: 8/8/10

Original Gravity: 1.058 (1.045 - 1.060)
Terminal Gravity: 1.015 (1.010 - 1.015)
Color: 19.12 (10.0 - 17.0)
Alcohol: 5.72% (4.5% - 6.2%)
Bitterness: 36.2 (25.0 - 40.0)

Ingredients:
10.0 lb 6-Row Brewers Malt
2 lb American Caramel 80°L
1.0 oz Cascade (5.5%) - added during boil, boiled 60 min
1.0 oz Cascade (5.5%) - added during boil, boiled 20 min
1.0 oz Cascade (5.5%) - added during boil, boiled 5 min
1.0 lb Victory® Malt
1.0 ea WYeast 1056 American Ale

I'm not quite in the "accepted ranges" but whatever, just trying some stuff on my own. Anyway, I came close to my expected OG and came in at 1.056, and pitched a 1L starter that took off VERY quickly when I made it, just healthy yeast I suppose. I had good fermentation going with 3-4 hours and it continued for the the next 48-72 hours. It all but stopped after that, so I checked the gravity today just to see where I was and to be sure I didn't have a stuck fermentation. I measured it right at 1.008 which is a little low. I'm not complaining, I like dryer beers and it tastes fine right now, I'm just curious as to what would cause such a low FG. I did mash at about 150˚F for 70 minutes, so I suppose that could be a contribution as well as just good healthy yeast.

What say you HBT?

Mashing at 150 for 70 minutes would give you a more fermentable wort, and hence a drier beer, than if you mashed at a higher temperature. I usually mash AAAs at 153-154 for 45 minutes to an hour. I only mash a couple of beers at 150 or less- usually IIPAs or beers that I want to finish dry. I mash beers that I want "thick" and dextrinous at 156-158. Temperature really plays a big part in the finish of a beer.

Another thing to keep in mind is that your thermometer is only 2 degrees off, you could have mashed at a very low 148! I know that I had issues like that a couple of years ago, and all of my beers were finishing under 1.010, that's why I mentioned it.

Of course, using two pounds of crystal malt should have given you a higher amount of residual sweetness and a higher FG so I'm surprised it did finish at 1.008.

YooperBrew said:

Another thing to keep in mind is that your thermometer is only 2 degrees off, you could have mashed at a very low 148! I know that I had issues like that a couple of years ago, and all of my beers were finishing under 1.010, that's why I mentioned it..

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I figure it mostly is the mash temperature. I was aiming for 154˚, came in at 151˚, and dropped to 150˚ during the mash, but it was my first run so I was happy. That's a good point that the thermometer could be off. This little digital one I have seems to be dead on at boil, but about 2 degrees warm at freezing, so who knows where it's at in the 150's range. Any recommendations for a good and accurate digital thermometer with a probe on a wire?

YooperBrew said:

Of course, using two pounds of crystal malt should have given you a higher amount of residual sweetness and a higher FG so I'm surprised it did finish at 1.008.

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Yeah, my local home brew store only sells grain by the pound, so while I only wanted to use 1.5 pounds of crystal, I had to buy 2 pounds. When I doughed-in, I wasn't paying attention and dumped the whole 2 pounds in instead of measuring it out. Whoops.

Where did you get your "accepted ranges" from?
I know that Beersmith pays no attention to the mash temperature (which can have a considerable affect on attenuation), but I use Promash (which doesn't even try to guess the FG).
I did some research on this a few days ago, and find that I get 75% to 80% apparent attenuation when using WLP002 with a mash using 100% grain, yet White Labs say 63% - 70%. I checked with White Labs and they confirmed that their published attenuation figures are apparent, rather than real.

-a.

ajf said:

Where did you get your "accepted ranges" from?

-a.

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Probably the BJCP Styles. I'm only, of course, guessing based on the part of the post that stated "10-B American Amber Ale". One of these days I will start brewing the styles so I can sample what BJCP purports to be the style.

And to the OP, yes that low a mash will usually yield a drier finished beer. Next time try a bit higher and compare the two to really see the difference subtle changes can make.

suprchunk said:

Probably the BJCP Styles. I'm only, of course, guessing based on the part of the post that stated "10-B American Amber Ale". One of these days I will start brewing the styles so I can sample what BJCP purports to be the style.

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Exactly right, I rarely followed the styles and ranges to the letter though. I just used them as a guide to get me in the ballpark of what I wanted my beer to taste like.

suprchunk said:

And to the OP, yes that low a mash will usually yield a drier finished beer. Next time try a bit higher and compare the two to really see the difference subtle changes can make.

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I definitely will next time, I don't mind a drier beer, I was just curious as to why my FG was lower. Thanks for the input everyone!