Low attenuation

Could someone give this a look and see if you can figure why I got such a high final gravity? I oxygenated the hell out of the batch before pitching with a hook/whip thing on a drill, and fermented in two 6-gal better bottles. I used two tubes of fresh WLP005, one tube per carboy. Fermentation started quickly and looked vigorous for at least two days. Kept at roughly 70 degrees F. Still in the carboys after about a month.

Mashed at 152F for 75 minutes. 1.5 quarts water per pound grain.

11.3 lbs (85%) Rahr 2-row
2 lbs (15%) Briess 40L Crystal
2.1 oz goldings 60 minutes
1.2 oz fuggles 20 mintes
1 oz goldings 10 minutes
1 oz fuggles flameout

10 gallon batch (11 gallons fermented)
OG 1.034
IBU 31
SRM 6.5

FG 1.015 (expected 1.007)
(attenuation 55.9%)
(ABV 2.5%)

What was your mash-temp? Have you checked/calibrated your thermometer to be sure it is accurate?

How old was the yeast pitched? Check the date on the tube. How was it stored, handled prior to pitching (warm, cold).

Did you pitch at 70F or pitch warmer, then allow the fermentation to cool to 70F?

Mash was 152. I double checked the temps with multiple thermometers.

Unfortunately I don't have the tubes, but I used them a day or two after purchase. Stored in the fridge. Pitched at close to 70. Maybe a degree or two above. Fermentation looked really good considering the low gravity. I used blow off tubes and they chugged nicely. Decent kerosene, but none blew out. No changes to any of this compared to many other batches. Just that this is the first batch I've done with such low gravity.

If you experience stuck fermentations or low attenuation, and you have eliminated other variables such as: temperature, low pitching rate, poor aeration, age, etc., then lack of necessary minerals may be a significant factor. You may want to try a yeast nutrient like DAP.

Is it too late to add nutrients now?

Actually, the FG of 1.015 would be expected with 2 pounds of crystal malt in there. To get something like 1.007 is unreasonable, so your Fg prediction is flawed here.

To get a FG of something under 1.010, I'd have to mash at 149 or lower, use very little (or no) crystal malt, and probably add some simple sugars.

Your FG is fine. The beer is done, not stuck.

The non-fermentables from the crystal then? I didn't know it would account for such a big drop in attenuation.

So my ABV at 2.5% is actually a plus if it's true. I was actually trying to push the lower limits of gravity and ABV as a pet project for good lawn mowing ale.

It is too late. It should be used in either your yeast starter or at the end of your boil. This is a very common problem when brewing with RO water.

apeltes said:

The non-fermentables from the crystal then? I didn't know it would account for such a big drop in attenuation.

So my ABV at 2.5% is actually a plus if it's true. I was actually trying to push the lower limits of gravity and ABV as a pet project for good lawn mowing ale.

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Yes. 15% crystal means a lowered attenuation, unless you try hard during the recipe formulation and mashing to work around it. A lower mash temperature and some simple sugars would help with that.

An american red (amber) typically does use up to 12-15% crystal malt, and a typical FG is 1.012-1.015.

chawn said:

It is too late. It should be used in either your yeast starter or at the end of your boil. This is a very common problem when brewing with RO water.

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No, it's not at all a common problem with using RO water. RO water is an ideal water to start with, as malt has all the magnesium and calcium needed for a healthy fermentation.

Some people like to add some salts like gypsum for flavor, but it doesn't affect attenuation rates.

You are probably the last person on this forum that I want to argue with, Yooper. You have provided me with invaluable information both directly and indirectly on how to improve my processes especially after switching to all grain.

Usually the wort does supply all the necessary mineral requirements of the yeast EXCEPT for zinc. I used your water chemistry primer post to brew with RO water and followed it precisely (my tap water is awful) and couldn't get my FG below 1.020.

After researching, I discovered that a zinc deficiency was likely my problem. The remedy was simple: add yeast nutrient. It worked! I no longer have low attenuation.

I still use the guidelines from your post. But now I use yeast nutrient in my starter if I'm using one, or at the end of my boil if I'm going to use dry yeast.

I can't argue with your experiences with a zinc deficiency- but it seems to be anecdotal in this case. If adding zinc works for you, that's great.

There are some studies which suggest zinc can be detrimental when in a high quantity, as well as some studies which suggest that sufficient zinc IS extracted from the process of making wort.

I love braukaiser's experiments, and here is a write up of an experiment in adding zinc to wort: http://braukaiser.com/blog/blog/2012/06/22/the-effect-of-zinc-on-fermentation-performance/

In any case, if adding zinc works for you that's great. But there really shouldn't be any reason why RO water would be dismissed as it really is a perfect place to start for brewing.