Reusing Oil Once?
I'm having guests over for latkes tomorrow. I have the oil in which I fried latkes a couple of days ago, and oil in which I fried sufganiyot last night. Should I consider re-using this oil to fry more latkes? (The sufganiyot oil looks perfectly clean, the latke oil less so.) Or must I use another quart of fresh oil? I do not want to do anything that would compromise the quality of the food I serve my guests -- It just seems so wasteful to use so much oil....
I would pour it through a sieve and use it, definitely. I think combining them would work best.
I reuse oil all the time. I just strain it and keep it in a sealed container in the cabinet. If I fry meat in it, I reuse it once to fry another meat item and then discard, but if it's potatoes or something, I'll use it 2-3 times.
I use the oil in my fryer multiple times. I strain it after about every other use and then top it off. In the rare cases where I fry beef in it, I change the oil afterward ( so I only use it for beef if the oil is getting old ). I reuse oil from pan frying, too, but I toss it after frying beef, and sometimes after pork. I strain it though filter paper. Generally, if the oil smells OK, I will re-use it.
It depends how hot you got the oil to and what kind of cooking oil as well. The hotter you get the oil, the faster it degrade. Refined oil is better than unrefined oil for re-use. Most restaurants do reuse oil.
According to Modernist Cuisine, you're likely to get a better product with moderately used oil - they even recommend, for folks who fry often, adding a couple Tbs old oil to a new batch to jump-start the "used-ness." If I remember, color is the main improvement.
(Obviously if you fry once a year, your old oil will go rancid before you can add it to the new oil. Also, I can't remember the chemistry behind the recommendation.)