Gravity contribution from powdered peanut butter?

[Suthrncomfrt1884]

I don't know enough about sugars to figure this out and I'm hoping someone can help me.

I brewed an Imperial Reese's Stout a few months ago, and I'm trying to figure out the estimated gravity of the beer. My measured OG was 1.090, and after fermenting it for 4 weeks, it was holding steady at 1.021. I then added 2 6.5oz jars of PB2 powdered peanut butter.

PB2 contains sugars, but I'm not sure if they're fermentable or how much they should contribute to gravity. Here's a little info on the PB2...

PB2: Powdered Peanut Butter
Ingredients: Roasted peanuts, sugar and salt.
Serving size: 2 Tablespoons (12 grams)
Servings per container: 15
Amount per 2 Tablespoon serving (when mixed with water):
Calories: 45
Calories from fat: 13

Value and % Daily Value*

Total fat 1.5 g 3%
Saturated fat 0 g 0%
Trans fat < 0.01 g
Cholesterol < 0.01 mg 0%
Sodium 94 mg 4%
Total carbohydrate 5 g 2%
Dietary fiber 2 g 8%
Sugars 1 g
Protein 5 g
Vitamin A < 1%
Vitamin C 0%
Calcium <1%
Iron 0%

My reason for concern is that I measured my gravity after 3 weeks in secondary and it held steady at 1.031. I wouldn't think the little amount of sugar would add much more than 10 points, so it leads me to believe they're unfermentable.

My beer has been in bottles for 3-4 weeks now and tastes like green apples pretty bad. I know this is caused by the yeast not cleaning up, but I'm not sure why I would have that issue with such an extended fermentation. Either way, 3-4 weeks in the bottle means it's just getting started. I'm giving this out as part of a xmas sample pack, and wanted to know how long to tell people they needed to wait before drinking it. I'm thinking that 4 months should be plenty for this to condition out the green apples.

Can anyone tell me whether the 1.031 gravity sounds about right? Or is there a chance I bottled a stuck fermentation?

 

[samc]

I would expect that your specific gravity would change from the addition of salt as well as sugar. I'd also think that salt could effect the fermentation, don't ask me how! I leave that to the science guys among us.

I doubt you would really want to give these bottles out in the hopes that several months down the road they might be drinkable.

 

[pikledbill]

Just to be clear here:

you added two 15 serving containers (total of 13 oz)? I took the totals listed and multiplied them by 30 (for two containers of 15 servings each)...Is this correct?

If this is the case, you added 30 grams of sugars (~1 oz), 150 grams of protein (~5 oz), 45 grams of fat (lipid, oil, ~1.5 oz), 60 grams of fiber (soluble?, ~ 2oz), 2.8 grams of salt (~0.1 oz), 150 grams complex carbohydrates (complex sugars/starch, ~5 oz)...etc. NOTE: all estimations.


All of these ingredients will affect your gravity...you added nearly a pound of gravity altering ingredients with the PB. Tough to know how much the gravity would change...there is a lot going on here. You don't know the profile of the sugars in peanut butter (i.e. the fermentability of the peanut butter sugars).

I don't know if beer calculators will take into effect lipids, fiber, etc. (to yield an approximate FG). Also, I am assuming soluble fiber...it may be insoluble (and so may not affect your gravity much). You did not take a gravity reading directly after adding the PB (that would help some)?

You might be able to get a reasonable estimate for the change in gravity due to peanut butter if you assume that all non-fermentable ingredients are non-fermentable sugar (when you punch numbers into a beer calculator). Use your 1.02 RG as an IG, and add the PB ingredients with the calculator to get the change in gravity...you will have to ignore the expected final gravity estimate from the calculator though, as it won't make sense. You might try assuming that the simple sugars will be fermented (30 grams), and that the complex sugars will not (150 grams)...but this is a guess on my part. I am not sure if I am making this better or worse. I never use calculators, and I don't know all the tricks one can use with them.


Salt (NaCl) only begins to inhibit yeast at >1%...is this a 5 gallon batch? You are well below 1%.

Off the top of my head, your ABV is getting up there even before the PB? Have you hit the tolerance limit of your yeast? Is it carbonated in the bottle after 3-4 weeks? Did you add another sugar source at bottling?

Not a lot of help here, sorry...I have to punt, you need a better brewer than me. But maybe there are some things to think about here.

I don't know how long it will take to condition...depends on how happy the yeast are. Keep a twelve back and keep tasting it every month...when it is ready, give everyone a call and tell them. This gives you a chance to keep in touch after X-mas.

Cheers,
Pikledbill