Need Some Clarification Regarding FG

I've heard 2 schools of thought with regards to FG and bottling. I just checked on my stout after 24 days in the primary.

Target OG: 1.055
My OG: 68* @ 1.052 = 1.053 (68% efficiency)
Target FG: 1.015
My FG: 1.021

I tried rousing the yeast, upping the temp, and waiting 7 more days to see if my FG would come down. It has not.

There are some folks here that will advise that with a higher than predicted FG, you may have bottle bombs, while others will state that "when it's done, it's done."

I'm curious to know what the true answer on this is. The thought about bottle bombs is that there are still uneaten sugars in the beer, and when adding corn sugar to bottle, will set off a new fermentation.

Thoughts? I'm bottling this regardless, but I'm just curious as to whether or not we can get a firm answer on this.

Did you do your own mash or is this from extract?

If it is from extract, you should hit your OG and your FG should be pretty darn close to projected (based on the yeast attentuation %). Commercial extracts are done under very controlled conditions are incredibly reliable in terms of fermentation properties. If you miss FG substantially, something is wrong. Either your yeast weren't healthy enough to finish the job or something stopped them (floc'ed out, big temp drop etc).

If you mash yourself, then you introduce the possibility that something went wrong in that stage. OG only measures the total sugar in the wort. It does not ensure that any particular percentage of those sugars are fermentable. If you ended up with more unfermentable sugars than your calculator assumes, you won't hit the calculated FG no matter how long you let it sit. You also still have the possibility of a fermentation problem.

billl said:

Did you do your own mash or is this from extract?

If it is from extract, you should hit your OG and your FG should be pretty darn close to projected (based on the yeast attentuation %). Commercial extracts are done under very controlled conditions are incredibly reliable in terms of fermentation properties. If you miss FG substantially, something is wrong. Either your yeast weren't healthy enough to finish the job or something stopped them (floc'ed out, big temp drop etc).

If you mash yourself, then you introduce the possibility that something went wrong in that stage. OG only measures the total sugar in the wort. It does not ensure that any particular percentage of those sugars are fermentable. If you ended up with more unfermentable sugars than your calculator assumes, you won't hit the calculated FG no matter how long you let it sit. You also still have the possibility of a fermentation problem.

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All grain. Mashed myself. Here are the details:

Strike temp 158
Mash temp 154
Covered and put in pre-warmed oven for 60 min.
After 60 min, took out and took temp. Temp was around 154/153

I'd guess the mash then. Temps are a little high if going for a dry style. You might drop that a couple of degrees and add a few extra minutes on for good measure. If this was the stout in primary #1, the water chemisty is slightly different for that than any of those lighter beers. Did you test ph? The extra acid from the highly roasted malts can also impact conversion depending on your water.

Anyway, my money would be on no bottle bombs for you.

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If the beer is truely done fermenting, I don't think you'll have bottle bombs due to the high FG. The residual sugars are there and the yeast have already decided not to ferment those. You can wait a few more days just to make sure you've reached terminal gravity, but I think you're safe from bottle bombs.

You got about 60% attenuation, which is low. Perhaps there weren't enough healthy yeast pitched, or temperature control was off. Your mash temperature could have contributed to a slightly higher FG as well, but mashing at 153-154, I don't think that's your issue. What yeast did you use and did you make a starter?

Anyway, I hope the beer still tastes good, even if it's a little sweeter than you wanted.

Some common causes of poor attenuation:

High mash temps
low pitch rate or yeast health
lack of oxygenation pre-pitch
Some combination of these or other factors.

On the plus side, 1.021 isn't terribly high, and in a stout you'll probably enjoy the very slight (or unnoticeable) residual sweetness. So, RDWHAHB!

Some yeasts do stall. My thought is if your gravity hasn't dropped with the things you've tried and it has been consistent for 7 days or more, you can bottle without risk. You can try another yeast to dry it out, if that's what you're seeking. It's commonly done for some Belgians.

What was the recipe? Maybe there are a lot of unfermentables and it could be done.

I agree with frazier but I was also thinking of mash conversion!

Did you check the mash for conversion?

It is possible you did not get a full conversion from your grains (few drops of wort in a few drops of iodine and check for black) black means unconverted starches which will most like not ferment!

Just something to think about!

Here was my recipe. This was a 1-gallon batch, so I do not make starters, and I usually round UP per MrMalty's pitch rates:

Malts and Fermentables
Pale 2-Row- 1.50 lb
Caramel/Crystal Malt 60L- 0.30 lb
Roasted Barley- 0.20 lb
Pale Chocolate- 0.15 lb

Hops
Chinook- 0.09 oz @ 60 min. (11.8 AA's. Recipe calls for 24 IBU's).

Misc.
1/5 Whirlfloc tablet @ 15 min.

Yeast
US-04- Per MrMalty, pitch: 0.2 packets (rounded to .5)

(Based on 70% efficiency)
Target OG: 1.055
My OG: 68* @ 1.052 = 1.053 (68% efficiency)
Target FG: 1.015
My FG: 1.021

Strike temp 158
Mash temp 154
Covered and put in pre-warmed oven for 60 min.
After 60 min, took out and took temp. Temp was around 154/153
Heated wort to 170 and cut the heat, covering and let sit for 10 min.
Removed bag after 10 min and squeezed out all remaining wort and brought to boil

Added hops/etc as per above

After 60 min., cooled down to 70 degrees, strained, and took OG reading (see above)

Shaked the ever loving hell out of the carboy for about 2 minutes.

Pitched yeast at 4:30 PM

Added a few drops of Fermcap S.

Put into fermentation chamber. Ferment at 66 degrees for 21 days.

After FG met, cold crash 48 hours and bottle.

You've got roasted malts as 30% of your grain bill. All of those dramatically lower mash PH. If you drop below 5, the main enzyme that is producing the simple malt sugars really slows down. ie you get starch converted into big sugars, but it isn't broken down enough for the yeast to process.

If you are going to brew stouts, you should pick up some PH strips and calcium carbonate.

billl said:

You've got roasted malts as 30% of your grain bill. All of those dramatically lower mash PH. If you drop below 5, the main enzyme that is producing the simple malt sugars really slows down. ie you get starch converted into big sugars, but it isn't broken down enough for the yeast to process.

If you are going to brew stouts, you should pick up some PH strips and calcium carbonate.

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Interesting. I followed a successful recipe though, so how could it have gone wrong?

What do you mean "if you drop below 5?

I have PH strips...What do I do next time I brew a stout?

I think the pH was ok, but the high FG comes from the higher percentage of crystal malts (it looks like .30 pounds in a 2 pound batch? That's a lot of crystal malt). All that means is combined with the higher mash temperature, the wort isn't all that fermentable- I'm certain you got conversion and the mash pH certainly wasn't under 5 and you don't need to add chalk to your mash!

Anyway, the higher FG is a combination of those factors- the higher crystal malt percentage and the higher mash temp ( I suspect the "warmed oven" kept it warmer at the beginning). It's fine, and if it stays where it is, it's ok to bottle.

It REALLY depends on your water. You can have the same recipe, but if you start out with different water, you can get dramatically different mashing results.

eg you can't make a stout in pilsner without altering the water. It doesn't work. It just doesn't have enough naturally occurring chalk to balance out the acid of a bunch of highly roasted malts. In distilled water, the mash ph for caramels and roasted malts is down in the 4's. The famous stout regions like ireland have more naturally occurring chalk to perfectly balance. It isn't an accident that certain styles developed in certain regions.

Missing the PH range is very much like missing your temps. It isn't an all or nothing proposition. The closer you are to ideal, the better conversion you get. If you've got you PH strips already, test it a few minutes into the mash. If low, add a little calcium carbonate (there are online references to give approximate amounts, but it really depends on your water.)