Missing my gravities....why?

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huge1s

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Brewed over the weekend, a kit from Austin Home Brew and the recipe said the expected post boil gravity should be 1.057. Mine came out to 1.051. My efficiency was 75% (it was 78% the last time... so pretty consistent). I ended up sparging 2 quarts more than I needed for my 6.5 gallon pre-boil volume, but wouldn't think it would make that big of a difference. Everything I have read said that the kits assume 75% efficiency. My first brew day from an extract kit had the gravity almost exact, so I don't think it is my hydrometer. Any clues or a starting place to look for my lower than expected gravity? Water maybe?
 
How long are you leaving it in the primary fermenter? Try leaving it in the fermenter for 10 days..... Another thing could be the yeast you are getting... I order kits from Austin Homebrew all the time but I do not buy their liquid yeast Reason I do not buy their Liquid yeast is because even with ice pack the yeast gets too hot.. I live in Georgia so comming from texas by the time I get my yeast its dead as a door nail.. If all else fails make a huge ass starter.
 
If you added an extra 2 quarts (0.5 gallons), this would account for the difference.
 
How long are you leaving it in the primary fermenter? Try leaving it in the fermenter for 10 days..... Another thing could be the yeast you are getting... I order kits from Austin Homebrew all the time but I do not buy their liquid yeast Reason I do not buy their Liquid yeast is because even with ice pack the yeast gets too hot.. I live in Georgia so comming from texas by the time I get my yeast its dead as a door nail.. If all else fails make a huge ass starter.

Really this was a question about starting gravity after I am done boiling (before pitching). If my efficiency matches what the kit was designed for... shouldn't I be pretty close?
 
If you added an extra 2 quarts (0.5 gallons), this would account for the difference.

I guess that would make sense.... because the sugars would get diluted more. I re-calculated my efficiency and changed the pre-boil volume from 6.5 to 7 and it made a difference. My system was actually more efficient (81%). Next step is to dial in my water calculations. My mash tun is not big enough to hold a 5 gallon sparge, so I split it into two sparges. My dead space is .25 gallons, so I added an extra quart to account for having to do two sparges. I also went back and looked at the recipe and it calls for 6.25 gallons pre-boil... and I did my water calculations for 6.5. There would be my two quarts.
 
I guess that would make sense.... because the sugars would get diluted more..

it'd only be more dilute if you didn't boil it down to the same volume. 2 extra quarts pre-boil wouldn't account for the difference even if that much extra was left, i.e. 5gal * 57 = 285 > 5.5gal & 51 = 280.5.

there are many things that can effect your efficiency. id read this and see if anything stands out: http://braukaiser.com/wiki/index.php/Understanding_Efficiency
 
It calculates out to 1.0518 (57*(5/5.5)) which, in my book, is pretty darn close.
 
I should also explain that I threw out the two extra quarts at the end of the last sparge. Why? Not exactly sure, but I was worried about having too much wort in my brew kettle (boil over). So the gravity reading pre-boil was for 6.5 gallons. I used that calculator on brewer's friend to figure my efficiency.
 
And maybe I am not understanding this correctly.... but it sounds like this is a water volume problem. At least conceptually.... If a recipe was made assuming a 75% efficiency, and I achieve that.... the gravity readings should be pretty close to spot on if my pre-boil and post-boil volumes are accurate according to the recipe. I can get the same gravity reading with a higher volume if my system is more efficient than 75%. If my system is 75% and I have a higher volume, then my gravity should be lower. Am I thinking about this correctly? Also, is there and equation for figuring out how much to boil off to achieve a specific gravity, given the pre-boil gravity and volume?
 
Gravity beginning x volume beginning = gravity end x volume end

you wanted 1.057? You had 1.051 pre boil? 6.5 gal? so 51 gravity unit x 6.5 gal =331.5 now divide this by finishing volume 5.5 gal = about 60 so 1.060

You need your pre boil gravity and volume to give you your brew house efficiency and how much you need to boil to hit your target OG.
 
Just to help with an example say you have 7 gal of 1.050 wort you want an OG of 1.060

Just take the numbers past the decimal for the gravity so 50 x 7 gal = 350 this is your total you want 1.060 ....so 350/60= 5.83 gal so you want to boil off 1.17 gal. I know I boil of 1 gal an hour so I would boil for 70 min to get that gravity.
 
I had a pre-boil gravity of 1.044 (6.5 gallons) and a post-boil gravity of 1.051 (5.5 gallons). I was shooting for 1.057 post-boil gravity. Thanks for the calc... that will help me a ton next time if I figure out I am far off my gravities.

So, I would have needed to boil down to a smidge over 5 gallons to get the gravity I was looking for. 44*6.5 = 286, 286/57 = 5.017 gallons.
 
Me personally I don't care about my gravity reading. But then again I use batch sparge method. All I Care about if it taste good.
 
I care I like to know my ABV and estimate my IBU. Also, knowing my efficiency helps with my recipe design. I like to make a lot of hoppy beers but have a balance with IBU:GU of some sorts.
 
Thanks for all the feedback guys. It really looks like I need to dial in my water calculations and figure out my system a bit more. The good news is that my system was fairly consistent in terms of efficiency from the first batch to the second batch. I am not all that concerned about a lower ABV than expected, but more concerned that my process is a little "loose" when it comes to my water calcs. Here are a couple things I need to measure out in my system:

Grain Absorption Ration
Boil Off Rate
Mash Tun Heat Loss/Hour

I am not sure what else I need to figure out to dial in my system (I already have dead space calculated)
 
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