Beer Forum

I have been listening to several of Jamil's webcasts, and I am stumped at final gravity numbers.

After a dozen PM batches, most seem to finish at 1.010 to 1.012.
I am using dry yeast, Nottingham, and S-23 Saflager. Plan to try S-05 in the next few batches.

I know the mash temp affects the fermentability, available sugars, etc, and the yeast chosen affects it.

Most yeasts list 70% - 75% attenuation and often Jamil uses 77%-78% to reach his final gravity.

What is the proper formula? What am I missing?

Not sure what you are asking here. The attenuation percentage is directly related to the variables you mentioned. A specific example would help to clear things up. Are you brewing the same beer using the same recipe, procedure, and yeast that Jamil is using and still coming up short of your target final gravity? Are we comparing apples to apples? If not there may be a bit of difference in your final gravity and you may have to adjust your recipe/procedure in order to hit your target.

Take your starting gravity, subtract one, and multiply by 1000 to give you a whole number (or to make things simpler just use the number after the decimal as a whole number). Then take your final gravity and do the same. Subtract your F.G. from your O.G. and divide by your O.G. That will give you your attenuation percentage.

O.G.= 1.060
1.060-1=.06 .06x1000=60


F.G.= 1.012
1.012-1=.02 .02x1000=12


60-12/60= .8 or 80% attenuation.


Whew...! I'm very sweaty now.

Beware of the PM too. Using the DME or LME can add varying amounts of fermentables. Each extract has a different amount of unfermentables in them that will lend a themselves to a higher or lower FG.

Brew on.

Sean

Right, but in your example, you show 80% and most yeasts list 70%-75% max attenuation.

So, based on the OG points (60 in example) should you expect the yeast to ferment 70%-75% of that?

IE 60 * .75 = 45 points which leaves 1.015 FG?

Or can a healthy yeast with an adequate starter ferment higher, like the 80% you show?

And for extract, if it is 70% fermentable then 75% of 70% = 52.5%??

Remember, this is called APPARENT attenuation.
The yeast APPEARS to ferment x% of the sugar.

The numbers are deceptive, because the alcohol that is produced weighs less than the water, increasing the apparent attenuation level.

A good example is something like Michelob Ultra - it ends with a gravity of around 0.0098 - in other words, assuming an OG of 1.040, it ferments out 42 pts out of 40 or 105%.

Obviously, it can't ferment out more than 100% of the sugar, so the numbers are only approximations for what can easily be observed/calculated.

I agree with all of what everyone else said, but let me add this. If you're sure you're measuring a lesser attenuation (you've calibrated your hydrometer, right?) then you might need to adjust your procedure or ingredients. If you're all-grain, most likely your thermometer and mash tun isn't identical to mine, so feel free to drop a degree or two in the mash if that is what it takes. If your extract is less ferementable, then you might want to add a dash of simple sugar in place of some of the extract.

Of course, the first place to look is the health and pitching rate of your yeast. If that is in order, then tweak the other parameters until the FG falls in line.

BYOHB wrote:Right, but in your example, you show 80% and most yeasts list 70%-75% max attenuation.So, based on the OG points (60 in example) should you expect the yeast to ferment 70%-75% of that?

Once again there are many variables to consider but in a nutshell, that would be a fair expectation depending on the yeast strain, wort composition, and fermentation conditions.

BYOHB wrote:Or can a healthy yeast with an adequate starter ferment higher, like the 80% you show?

Absolutely. The attenuation percentage stated for each yeast strain refers to the degree of attenuation achievable in an all grain wort of a basic base malt composition. If your wort were to be composed of more highly fermentable components such as simple sugar or honey, the achievable attenuation percentage would increase.

BYOHB wrote:And for extract, if it is 70% fermentable then 75% of 70% = 52.5%??

If a wort is composed of an extract that is 70% fermentable, than technically a yeast strain with an attenuation potential of 75% would ferment that wort to a full 70%, assuming the planets are aligned and all is right with the world.

What percentage of sugar can you go up to before it changes the flavor? I have made several extract beers from JZ's book and all finish at a higher FG with the appropriate starter. A few I even added 2-3% cane sugar to try to dry them out and I got closer but still not down to the recipe FG.