Rancid Sunflower Oil?

[Nik2WIN]

Aargh help!  I've always managed well with my mayonnaise but when we came back from holiday I threw together some mayonnaise which went together beautifully but tasted foul.  I couldn't put my finger on it and chucked it in the fridge thinking that I'd missed something out.  This afternoon I made brownies using sunflower oil again and they have the same yuk undertaste.

Is it possible that my sunflower oil has gone off?  I go through it like nobodies business but we had been away for a week.  Nevertheless it can't be much more than 3 weeks since it was opened ...?

Nik

[Cornish Cream]

Does it smell off Nik? I know oils can go rancid after being open for a few months.I'm sure you could return it to your supplier if it's off.

[Nik2WIN]

No it didn't smell off.  I do use organic oil so I wondered if it might "go" earlier but its the only thing (apart from eggs and they were from completely different places) that the 2 dishes had in common.

it wasn't just me, the children noticed the taste in the mayo - the brownies have just been thrown out!  I've got some new oil coming tomorrow - I'll try a bit of mayo before I go for the brownies again!  Its all used up now but I'm sure I could have returned it - it WAS Ocado after all 

Nik

[andiesenji]

Nut oils can rapidly become rancid if stored at higher temps and also if it is exposed to air for prolonged periods.
The critical temp seems to be about 80-85° F.  - 26-29+°C. 

I smell and taste any oil before using it in a recipe.  It is instantly clear that the flavor is off, as soon as you taste it.

I don't keep my oils in the fridge but I have a "cool room" where I store them and I make sure the cap is tightly fastened and store them in plastic buckets -up-side down.  This lessens the amount of oxygen (the great destroyer) that can get to the oil.

I store salad dressings, mustards and other condiments this way also - the reason I use containers to hold all these smallish bottles and jars in the fridge. 
(It also takes less time to search for one item and makes it much easier to clean the fridge.)