Hydrometer readings

[brewn]

A question popped into my head earlier today regarding taking hydrometer readings. I haven't tried this out yet, and I will on my next brew. But for those out there who use a hydrometer, when you read your sample, regardless of which one it is, do you let things settle out before taking the reading? I ask this because in my previous occupation, it was vital to understand how salinity affected buoyancy. Yes I know wort is not sea water, and I understand how the hydrometer physically works. However, it is the same basic process--stuff in the water (and temperature) affects buoyancy. We concern ourselves with bubbles on the hydrometer, hence giving it a little spin, to get a more accurate reading, so why not particulate that maybe floating in our wort? Anyone have any experience in this?
Like I said I plan on doing an experiment next brew by taking readings on settled and unsettled samples.

[Ck27]

You are taking a gravity reading which relates to how much fermentable sugars are in the wort, it doesn't matter really the surface tension, its meant to give you a idea of how much alcohol you have in your brew when you compare it to the end hydrometer reading.

[Roadrocket]

I let mine settle for a while but the temperature of the wort makes such big difference that I've never measured the effect of settling. After it's settled I measure the SG and Do a temperature correction using the beersmith tool. It'll be interesting to find out.

[durrettd]

Undissolved crud included in a hydrometer sample will not affect the hydrometer reading.

A boat floating in the same pond as the canoe you're paddling, doesn't affect the buoyancy of your canoe. The same principle applies to anything not dissolved in the liquid. In the canoe example, if you dissolve a ton of sugar in the water, your canoe will float higher; if you dump in a ton of rocks, the level of the water will rise, but your canoe will still float as deep as it did before. The same applies if you dump in a ton of ping-pong balls - the water level will rise, but the canoe will float on the same waterline.

When a solid is dissolved in a liquid, its molecules are interspersed in the liquid it's dissolved in, increasing the weight of the total volume of liquid, slightly increasing the volume, retaining its molecular structure, and not affecting the molecular structure of the liquid.

Yeah, I know. Too much information. But, now you're ready for the test. Everyone pick up your pencils and begin. You'll have 45 minutes.

[brewn]

I appreciate everyone's replies, and valid points. As a retired Submariner my brain wandered it's way back to how the buoyancy of the hydrometer was affected, other than the sugars. And, since curiosity still had the better of me, I'll be conducting my experiment this weekend. Even if I'm way of in my thought process, I'll post the results (with pics if I can figure out that part of posting)

[GigaFemto]

As pointed out, settling of material will not affect the hydrometer reading. I do see people make a couple of mistakes with hydrometer readings, though. If you look at the photos on Brulosophy you will often see the sample tube filled to the top, with the liquid surface bulging up above the walls of the tube. When I do that the reading on my hydrometer is a couple of points higher than when I keep the liquid level below the top of the tube. I also always measure at the base of the meniscus, where the flat liquid surface would intersect the scale, and not the top of the meniscus as many people do. I have read instructions about the latter point, but not the former. Has anyone else had the same experience with filling the tube to the top?

--GF

[brewn]

I can't say that I have. I typically have my hydrometer in the sample container and fill the container until the hydrometer is floating well enough. And that's Ricky about an 1 1/2" below the top.
The issue I hate is the fact that mine (and it may be a quality issue) doesn't sit perfectly vertical so there's a chance of it touching the sides.

[DrWill916]

Has anyone else had the same experience with filling the tube to the top?

--GF

I have a small ring at the top of my sample jar that keeps the hydrometer from tilting toward the edges. This makes it easier to read, so I just fill until i get a good float and the top of the hydrometer is sticking through the ring; I don't need to fill all the way to the top. That said, when I have done, I haven't seen any appreciable variation.

[brewn]

So... With more time passing before getting to brew than anticipated, I finally got to brew my Citrus Paled Ale and experiment to see if a sample which had time to settle would read differently than one where everything was still in suspension. Knowing temperature would play into this some I let both samples cool to 63 degrees. That just happened to be the outside temp. Of course by the time this happened, both samples had plenty of time to settle out. There was no concern of bubbles, as there were none. So carefully placing the hydrometer in the first sample as to not stir anything up I got a reading of 1.052. I then stirred up the second sample to get everything back in suspension and then took my reading. I got 1.054. Now, that's not really that much of a difference, however, I do think it does show, at least in part, that one may get a slightly better reading of just the dissolved sugars when letting your sample rest and settle out. Of course I'll try this again on my next brew if just to gain more data.

Happy brewing!

[durrettd]

Well..... Dang!
That's not the way I thought it worked!

[GigaFemto]

It would have been better if you used the same sample, settled out, and then stirred it up so you know they were exactly the same material at the same temperature. Are you measuring at the bottom of the meniscus? The meniscus, or curving up of the liquid along the surface of the hydrometer, is caused by surface tension and not by the density of the bulk. It may be that the junk you stirred up changed the surface tension enough to change the meniscus. I see the photos of hydrometers on Brulosophy (http://brulosophy.com/) and they routinely read the top of the meniscus, which is wrong (although a whole lot easier).

--GF

[brewn]

I see what you're saying there with using the same sample GF. That is a good point, and one that will be used on the next experiment. As for the meniscus, yes I was measuring from the bottom of it. I always do. My previous occupation dealt with it quite a bit, but If there was anything pounded into my head when I first started brewing other than sanitizing was reading the hydrometer correctly. I actually prefer the hydrometer over a refractometer. There seems to be a more fun science to it.
Alright....that sounded too geeky.