This is a “for next time” question - I’ve already pitched the bottle in question because I wanted to make some baked Xmas gifts and decided I wanted everything fresh.
I had a partially used bottle of Canola oil in my fridge (and I keep my fridge on the cold side) for several months and it developed quite a bit of white sediment at the bottom. The sediment was fairly light in weight; it mixed with the rest of the bottle easily if I shook it.
What was that? Was the oil turning rancid? Note that I have an extremely poor sense of smell; if you want me to check if it smells funny next time I’ll have to get a neighbour to check.
It was frozen oil. I keep my extra virgin olive oil in the fridge. It freezes even at 40 degs F. If I don’t use it for a couple of days, I have to put it in hot water for a few seconds, or briefly microwave it, to melt enough to use.
I have trouble accepting that it was frozen (congealed maybe, but I would still be surprised). It wasn’t a solid mass. Like I said it was easy to mix with the rest of the bottle if I shook it (making the oil cloudy, but the white stuff definitely dispersed through the rest).
Canola oil does have some saturated fat in it (7%), so I wonder if it has separated out, like when you cook meat and pour the residue out into a jar (at room temperature), which leaves liquid and semi-solid layers.
Nope, don’t worry about it. If you keep your oil in the fridge, you can expect at the very least some clouding. The difference between fats and oils is their room temperature state (this is due to their molecular structure). Fats are solid and oils are liquid. If you heat fats, they become liquid. If you cool oils, they become more solid.
Person ‘Educated in Chemistry, but never worked in the field’ speaking, here:
All ‘vegetable oils’ consist of a number of different ‘chemically pure’ (i.e. they are the same molecular structure) oils, all derived via extraction from some plant, and all mixed together, per cent quantities dependent on the plant you extracted it from. Some of those will have different freezing points than others.
If you extract the ‘oil’ from the source, you will wind up with a mixture of the ‘oils’ the plant contains. That’s still a (sorry, all cites are Wikipedia) ‘solution’, but you can have ‘liquid solutions’.
What you have experienced, here, is a liquid solution, where lowering the temperature of the solution will cause some chemical component of it to ‘precipitate’ out of the ‘solution’. It didn’t go bad in any meaningful sense. Don’t put the stuff in the fridge, and it won’t happen.
And it all goes bad in the same way. Or, more likely, not. I don’t keep any of my vegetable oils in the refrigerator. And none have ever gone bad. I’ve got ‘sesame’ oil that has not gone bad, after a freakin’ decade in my cupboard.
What you have likely experienced, here, is a higher molecular weight oil precipitating out of the solution. Heat the shit by ten degrees (F, or C, your choice, it doesn’t matter), and the ‘cloudiness’ will likely go away. Heat it to somewhere in the hundreds, and it will go away.
Some do, most don’t. Animal fats are likely to do so, which is why butter goes bad if you leave it out too long. Most vegetable oils are the wrong type of fat to go rancid rapidly. Hence my sesame oil that’s not gone bad in a decade of room temp storage.
It has to do with the saturation of the fat molecule, but I don’t remember what kind of saturated or unsaturated fat goes rancid. If they don’t refrigerate it at the store, you don’t need to, either, unless the package says ‘refrigerate after opening’.
Just my experience, but very pure vegetable oils never seem to get rancid. At least not the way butter does. The flavor does change a little over time. I don’t keep oils in the fridge, hasn’t seemed necessary. But I throw out butter soon after it’s opened because I can taste the oxidization.
In my case at least, I wouldn’t trust cooking oil not to go rancid if I kept it at room temperatire. I occasionally use a lot for one particular recipe that I like to make, but I make that recipe rarely, and all other uses are just a little bit at a time.
