How can one tell if oil is 350 degrees with out a thermometer? Are there any visual tells?
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when you think it is close, drop a cube of bread in. If it sizzles and browns in about that a minute you are good. If it burns in that time, it's too hot. But depending on what you are putting in, the food will cool the oil a bit at first.
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But first, what type of oil are you using? Some have lower "smoke" points than others. Usually you can tell when the surface starts to shimmy a bit.
Nutcakes has it right. If you don't have a thermometer the bread method is really the best way. That trick is old and steeped in the history of culinary.
You can also tip the end of a wooden spoon in the oil, if it starts to bubble around the tip, then the oil is ready.
I'm with Mr_Vittles. The spoon trick works for me, but more often I will use the tip of a wooden chopstick.
If you drop a grain of rice in the oil and it floats and cooks it's around 350
The bread (or cracker etc.) trick is more accurate, but with practice you can get a pretty good idea by flicking in a few drops of water and seeing how it reacts.
Some oils do develop a sort of hazy appearance with a certain temperature, but I'm not enough of a fryer to read it.