At home one needs some user experience to know whether the coconut oil is pure, rancid or adulterated .
Good and pure coconut oil will have a very natural pleasant aroma. The aroma will invite us to taste it. Pure coconut oil will taste good with a very mild sweetness of good ripe coconut. It will be smooth on tongue and easy and tasty to swallow.
f the coconut oil has gone rancid, the odour will tell us. A drop or two on our tongue will make us dislike it and may make us spit it out. But if it is just beginning to go rancid, then it may not be smelling so bad,but when tasted it will make us feel distaste at the throat end after we swallow.
How to know if coconut oil is adulterated with other oils:
Usually palm oil is mixed with coconut oil nowadays mostly, as palm oil is also used for cooking and is relatively low priced. It may not be very easy for all to identify palm oil adulteration if it is kept at low level percentages. But an experienced user can find it out.
The adulterated coconut oil will be more yellow than transparent white.
It will be less thick than the normal pure coconut oil.
On heating the oil in a vessel it will start smelling burnt even at lower heat.
In Kerala earlier Rubber oil was used for adulterating coconut oil. This can be easily found out, as the oil starts frothing immediately on heating it even at low temperatures.
Food items cooked with good and pure coconut oil will smell and taste good even after many hours.
Those food items cooked or fried in adulterated coconut oil will go rancid fast and start tasting bad after a few hours itself. The items may go cold and rough. But chips fried with good unadulterated coconut oil will be more crispy and will have more shelf life.
Pure coconut oil will freeze and solidify in relatively faster. If we keep a little coconut oil in fridge (no need to keep in freezer compartment)after about an hour or two so it would have started freezing. If any other oil or mineral oil are added,then they will either remain as liquid as a top layer, or lie as a membrane like layer.
If we dip a lamp wick or cloth piece in coconut oil and burn it, even the burning odour will not be that offensive.But if it has adulteration the burning odour will be offensive even in small doses.
There are chemical based analysis, but are not feasible or practical in our kitchen.