Attenuation and hydrometer vs. refractometer readings

Hey folks...

I've been having a strange issue of late in which I'm having trouble reaching expected FG in my fermentations lately. I just recently brewed a Witbier that started at 1.052 (based on hydrometer reading), and this just stopped doing anything at 1.020. I even gave it an extra week and raised the fermentation temp from 64F to nearly 70F, roused the yeast, etc, but to no avail. I expected a FG of around 1.013. Interestingly, while the hydrometer gave about 1.020, the refractometer read in at 6.5% Brix, which using the MoreBeer spreadsheet, comes up with a FG of 1.013. So, what's going on? BTW, this was mashed at between 148 and 152, and I was careful not to overdo the mash temp. I even added extra diastatic enzymes after 30 min. during the mash to ensure full conversion. I used a 2L starter of WLP400 (going into 11 gallons of wort). The taste of the beer seems fine, not overly sweet, so I think there is something strange going on.

Some thoughts:

1. Very high level of suspended trub out of the fermenter could possibly impact hydrometer, resulting in artificially high FG reading?

2. The refractometer correction is messed up by large amounts of non-fermentable sugars in the wort (that did not fully attenuate). This was brewed with 50% Belgian pale, 45% flaked wheat and 5% flaked oats.

3. ?

Thanks for any thoughts about this, as I've really been experiencing lots of FG readings higher than anticipated.

1. Trub doesn't affect hydrometer readings (unless your hydrometer is sitting on top of a pile of it at the bottom of the test tube.)

2. I haven't used a refractometer, but I know the calculations are different once there is alcohol in the beer, In other words, you use one calculation to find OG, but a different one to find FG. Some one else would be better at commenting on this.

WLP400 has an expected attenuation of 74-78%, and you're at 62% so that is a little low.

I'd trust your refractometer readings, as long as you use it for the OG and the FG. Carbonation can throw readings of FG off (if there are bubbles on the hydrometer, it will help to 'lift' it up, and give a higher reading than actual). Personally, I just use a refractometer, and it works fine for me, is easier, and obviously requires much less liquid. If it's a witbier (or any cloudy beer), it may fuzz out the reading a bit. If I have a cloudy sample, I'll put it in the fridge for a while to help clear it, and then pull off the top of the liquid where it's clearest.

Thanks for the posts! I agree that there could have been some CO2 or other bubbles leading to an artificially high hydrometer reading, though I am always careful to spin the hydro before reading. Nevertheless, that was a particularly out of whack reading, so I suspect something weird. I may need to just purchase a low SG hydrometer for FG readings. I do suspect that the issue was some unfermentables, but I cannot figure out why this would be given a long mash period at a lower temp. range. Maybe for experimentation purposes, I'll take some of the fermented beer and do an experiment by adding some extra diastatic enzymes to it to see how much lower it will go? I wish there was a simple way to test alcohol concentration!