I assume when you do a Hydrometer test for gravity you should let the sample sit until there are no more bubbles (oxygen) in the sample, correct? Doing a test right now and I see bubbles at the bottom bubbling to the top. That would askew the reading, right?
I don't remember ever letting my hydro samples sit for any reasons other than 1) to let the particulates settle, 2) to let it come closer to temp if it's inordinately warm or cool, or 3) to let the bubbles/foam dissipate from the top. The latter is so there won't be foam clinging to the stem of the hydro, making it a little more difficult to read. It'll be interesting to learn if that small amount of gas (whether O2 or CO2) would make a significant difference in the reading.
I checked it within a minute or so of filling the vial and it was at 1.02. I've been letting it sit now for about 15 minutes and spinning the hyrdrometer. Now the reading is at 1.014. Whenever I spin it I see bubbles floating to the top. I can also see bubbles clinging to the hyrdometer which I think would cause an inaccurate reading, right?
I usually get impatient with the bubbles on the stem, so I dip and wipe with a paper towel a few times. I’ll often use a shred of paper towel to lift the floating bubbles from the meniscus and to pull them up from the sides of the jar. I also typically don't take a reading until after a spin or two. Maybe that resolves a rising bubbles situation? I dunno. Temperature change? As temperature of the liquid increases, the volume increases and the density decreases. As density of the liquid decreases, the hydrometer will float lower, resulting in a lower SG reading. (I might be talking out of school here, so verification by someone more in the know is welcomed) Not sure how much of a temperature increase in 15 minutes would cause a 6 point decrease in SG.
You appear to have answered your own question. When checking for final gravity (or intermediate gravity) you should permit the beer to degas; the bubbles then are CO2 in solution (and over time coming out of solution). Cheers!
Neither do I. In my brewhouse room temp is upper 70s. I've heard of people in CO keeping their house at 59 for brewing. So here's where Mr. Thermo comes back into the game. Yes, and this may take a while. A couple of bullets: gravity will roughly vary by 1 point for every 8°F you vary from the hydro's calibrate temp (add for higher temps, subtract for low). If you forget which way to add/subtract there's a nifty calculator at Brewer's Friend that'll steer you in the right direction. Even with help with the math I find it most accurate to get the sample to calibration temp. Easiest is to put the whole kit-n-kaboddle in the fridge until the CO2 has off-gassed and sample temp is same as the hydrometer's calibration temp. The hydrometer's calibration temp should be printed, usually at base of the scale (typically 60 or 68). And you really should calibrate the hydro in distilled water at cal temp. I have some that are a couple of points high and some a couple of points low . . . just depends. A finishing hydrometer (expanded lower scale) makes the FG reading a breeze.
Yes, CO2 will skew a hydrometer reading, and degassing is a best practice. Waiting for the beer to degas requires some patience and also allows some evaporation, which can also skew the reading a little. Pouring the sample back and forth between two containers expedites the off gassing.
