[BigFoot]

My son and I love the local "All U Can Eat Fish Fry" place where my wife wouldn't be caught dead. She says I should buy more life insurance because I'm going to be gone while she's still in her prime. She's willing to bet that our son's engine oil is cleaner than the "sludge" they use in those fish fry places. This argument is rising to the level of WWIII.

Is there a professional out there who can speak to this? I'd simply like to know from a pro how frequently cooking oil is really changed at mid-level eating places. Please don't tell me there is no problem if the oil is replaced at regular intervals — that's the crux of my wife's argument: they don't replace the oil at regular intervals, they just add to it as it's used up.

The lady is a little neurotic on this subject. For deep frying at home, she buys the cheapest super-market oil she can find and uses it once. That causes me great pain — I mean the part about using it once.

[jbd]

You may both be correct. It all depends on the operator. One place I worked many, many years ago the use of oil was as follows. Starting with clean fresh oil on Monday the oil was filtered by draining the fryer. The fryer was cleaned and the filtered oil was returned to the fryer. This process was done twice per day. Tuesday the oil was filtered once after lunch rush and then at the end of the day the oil was drained from the fryer; the fryer was cleaned and then filled with fresh oil for Wednesday. This process was followed seven days a week.

Another place I worked at back then wasn't quite so fussy about the oil and it was changed once or twice a week based on business volume.

I am also aware that there are some owner/operators who follow the "add fresh oil as you need it to keep the fryer full" method and they never really feel the need to completely replace the oil more than 3 or 4 times per year. They may filter the oil once a week. Needless to say this is not good cooking and it usually is not good for the fryer and tends to lead to early equipment failure.

[kuan]

You should be able to taste old oil. You can also tell by the looks. Old oil is dark and dirty, and if the food is dark but not properly cooked, then chances are the oil is way old.

[shakeandbake]

I don't think the age of the oil should be your real concern. It's the "fish fry" & "All You Can Eat".

[Pete]

Most places change their oil at least once every 7-12 days, especially places that are busy and use the fryer a lot. They also are probably filtering it once a day. If not the stuff on the bottom just burns and makes the oil go bad more quickly.

[BigFoot]

I was so delighted by all the information provided, as was my wife who read every word. The happy consequence was we were now able to discuss this calmly. My wife is ready to concede that oil doesn't have to be discarded after every use, and I'm more susceptible to the idea that improperly used cooking oil can be a health hazard. From my wife's perspective, your answers beg the question: What do we filter the oil through for home use, and how is stored? Also, I agreed to do my All U Can Eat Fish Fry act at home once a week instead of at the "sludge" place.

[Jim]

What do we filter the oil through for home use, and how is stored?

Coffee filter works great for home filtering. Store it in a air-tight container out of direct light (UV breaks down the oil.. rancidity sets in... yuk!)

One little note for flavor... save some of the old oil to add to the new. There is a noticeable flavor impact when using clean oil; flavor actually intensifies as the oil gets older... for a while, then it will drop off. Save some of the older oil to get that preferred flavor.