Attenuation Math Help

[Hockeyhunter99]

i have usually used the math of [(OG-FG)/OG-1]*100% to solve for Yeast Attenuation. when i do the math on my $7 APA - i get 104.5% attenuation????????

this can't be right.

i have taken both measurements at the same temp using the same hydrometer.

OG= 1.044
FG= .998

I used a harvested Pacman that is in the 2nd generation.

1#-Dark DME (120min)
5#-Dextrose
(Found the recipe on BeerRecipes.org - thought i would try it- tasted great from the sample.)

 

[FensterBos]

How'd you get your final gravity under the gravity of water? Is that even chemically possible?

 

[BrewKnurd]

How'd you get your final gravity under the gravity of water? Is that even chemically possible?

its chemically possible because ethanol has a gravity less than water. but its not supposed to happen with normal fermentation.

 

[wonderbread23]

How'd you get your final gravity under the gravity of water? Is that even chemically possible?

Yes, it is possible. Alcohol is less dense than water. Your math seems correct. How does it taste? Certain wild yeasts and bacteria can super-attenuate a beer like that. I'd also check and make sure your hydrometer has been calibrated (it should read 1.000 with water at the temp. specified on the hydrometer).

 

[FensterBos]

That's why I like this forum I learn new things everyday.

 

[Hockeyhunter99]

i have a classic glass hydrometer that i use to check all of my beers. it is a laboratory grade.

the only thing i can think of would be the dextrose is completely fermentable and that would bring the SG below 1.000 if there is more ethanol than unfermented sugars. it tastes really good for warm, flat, green beer. even SWMBO liked the sample.


but 104.5% Attenuation????

 

[BrewKnurd]

i have a classic glass hydrometer that i use to check all of my beers. it is a laboratory grade.

the only thing i can think of would be the dextrose is completely fermentable and that would bring the SG below 1.000 if there is more ethanol than unfermented sugars. it tastes really good for warm, flat, green beer. even SWMBO liked the sample.

but 104.5% Attenuation????

What you actually calculate with that formula is apparent attenuation. Apparent attenuation is always higher than the actual percentage of sugar converted.

 

[Hockeyhunter99]

What you actually calculate with that formula is apparent attenuation. Apparent attenuation is always higher than the actual percentage of sugar converted.

Right. Actual Attenuation is another formula all together but i don't know how to use the numbers from FG and OG because they all say to drop the first two digits to find the points.

i.e. 1.044 would be 44. 1.010 would be 10

http://realbeer.com/spencer/attenuation.html

if i do that then my FG points reading would be 98 and that is not correct.

how would i use the equation from the link to solve for that?

 

[wonderbread23]

Did you really use 1# of DME and 5# of dextrose? If so, then that attenuation is no surprise. Dextrose is 100% fermentable.

 

[Lodovico]

You could easily hit that low of a FG if you really used 5 pounds of dextrose.

 

[ACbrewer]

try 44 an -2, since ytou are 'droping the first 2 values' but using OG-1 and FG-1 as your values.. so your FG-1 is .998-1 or -2 Gives teh AA of 105 and RA of 85%

 

[Hockeyhunter99]

Did you really use 1# of DME and 5# of dextrose? If so, then that attenuation is no surprise. Dextrose is 100% fermentable.

http://www.tastybrew.com/newrcp/detail/581

this is the recipe i came across. i will try the 44 and -2