I had some samples of WVO un-settle when I placed them in the sun.

The samples appeared clear dark brown in the waste bin but turned really slity, medium brown, gravy looking when I collected them.

I put a sample of each in a glass jar and sat on the garage shelf. Temps were probably in the 75-90 range in the last few days. In about 1-2 days it started settling real good. A bottom sludge layer and dack brown on top.

I put the dark samples out in the sun yesterday and the sludge layer disappered in a short period of time.

I thought that heat was supposed to help the settling process but it appears it caused the oil to mix up again instead.

Can anyone explain what happened? Does it need to be cold to settle the oil?

I may not be entirely clear on what you are describing....

Heating wvo to 80-90*F does help water quickly settle out. And in slighlty lower temps the heavier fats tnd to settle to the lower part of the storage container as well.

But when you heat the partially settled wvo it creates currents as the warmer wvo rises and the colder wvo fall to replace it. Once the wvo is all over 80-90*F the water will begin to settle out even if the wvo has small heat induced currents in it. But the fats will continue to mix until the heat stops being applied and the mix stops mixing itself due to currents.This is because the fats are much more similar in molecular weight to the lighter oils than the water is...I believe.

When you placed the jar in the sun it warmed the darkest least transparent stuff in it most...and it rose as it heated.

Hope this helps.

My samples were used veggie oil straight from the waste bin. No filtering or anything.

I was thinking about the best way to settle out used veggie oil before I filter it.

It appears that when cold/cool the most stuff falls to the bottom. Heat/sun seems to make the crap rise up though the "cleaner" oil.

I wonder if this cycle repeats daily, does the top oil get cleaner each additional cycle? Or does the crap at the bottom mix the same every day with the sun?

Basically, should I let this daily heating and nightly cooling cycle repeat for several days?

Or should I just dump the used oil into the settling tank and transfer/siphon it out the next morning?

I recommend settling a LOT LONGER than "the next morning" - weeks and weeks if possible. It gets better and better. The sludge on the bottom gets denser and the clear stuff on top gets clearer. The upper part of the opaque gravy-looking layer will become clear with warming regardless of mixing. Try taking a sample of this and see what it does at different temperatures. Also check out the posts by Tony from West Oz about burning this stuff; i.e. it's fine if warmed up.



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Another experiment...

I put my samples in the fridge. The samples were all dark brown, no visible sludge, at the time because the bottom layer had melted back into the oil.

I a short time the whole sample turned gravy.

I guess the rapid cooling caused the suspended fat to resolidify faster than it could "fall" to the bottom before the oil started to thicken & gell.

Probably the slower cooling at night allows the fats to solidify and fall to the bottom before the oil thickens up.

I bet the best thing for setteling is to place the barrel in a place that has minimal tempature variation. A cool, but not cold place. Without sunlight to prevent convection currenct inside the oil drum.

Once the oil has settled and been filtered, it probably doesn't matter much if it's stored where the temperature or sun varies as there is probably not much, if any, fats left in the oil anyway.