Missed my OG by a few points, should FG be off by the same amount?

[pensphreak]

On my last batch, my OG was expected to be 1.046 and I hit 1.050 (+0.004). My expected FG was 1.007, but actual was 1.012 (+0.005).

Is that true in general that if you miss your OG by 0.00x, you will miss your FG by approximately the same 0.00x due to the yeast attenuation staying the same?

 

[crocks86]

Attenuation will be about the same but it's a percentage, not a specific number of points. So if you miss your OG by 5 points your FG might only be 1 point lower. That's how it's generally gone in my experience. Your last batch seems to be an anomaly, maybe yeast weren't as healthy as expected or your mash was a little hotter than planned or something.

 

[Rockn_M]

If your attenuation % doesn't change you'll be pretty close to what your expecting however those % are averages. You could have a greater or lesser %. The biggest thing to remember is to keep fermentation temps in the range and stable.

 

[kev211]

In theory kinda. It wont be off by the same amount as the OG given that its a percentage. Unfortunately different yeasts attenuate differently and even different batches of yeast have some variances. Also all other environmental factors play into part (ferm temp, time in fermenter, grains used etc). I pretty much always use WLP001 and usually have an attenuation with a ~4-5% difference between batches.

For instance, one of my house IPA's I recently decided to add carapils to add more body. The OG was 1.068 vs the normal 1.062 and it finished up at 1.012 and 1.011 respectively. I think its jsut on the HB scale that its not as much of an exact science. I would imagine that larger breweries hit the same numbers everytime

 

[daksin]

I would still wait to see if it drops a bit more. I don't think you'd pick up that much in FG- some of those sugars you added should have been fermentable.

 

[chickypad]

The other thing to realize in addition to the comments above is that the original expected FG is just a best guess, based on software or some other calculation. Even if you would have hit your OG exactly you could have easily missed the expected FG by a few points. Trying to exactly predict FG's is a bit of a losing battle, unless you have a tried and true recipe and are extremely consistent in your practices. The best you can usually hope for is to be within a narrow range, then let the readings tell you what the true FG is.

 

[passedpawn]

If you miss your OG by X points, you'll miss your FG by one fourth of that (X/4).

So, if you're off by 4 points on OG, you'll be off by 1 point on FG.

This assumes 75% attenuation by the yeast, which is pretty typical.