How Often McDonald's Changes Its Frying Oil Might Surprise You

On its website, McDonald's says it filters its oil daily and changes it at "regular intervals" ... which is a bit of a corporate non-answer, and what it really means is actually anyone's guess. Because the truth, according to McDonald's employees, varies wildly.

So yes, officially each McDonald's restaurant is supposed to check and filter the oil every day. Filtering is when you use some mesh to clear out the debris to keep oil usable for longer, until it can't just be filtered anymore and needs to actually be changed out. Not having a strict and set rule around the oil changing makes sense if you think about it from the perspective that a McDonald's in the rural countryside might not be as busy as one in the middle of the city, and therefore will require less changes.

Over on TikTok, some former employees have shared that their locations swap their oil out once a week, which sounds fair, if a tiny bit gross. However, one Reddit post then dropped the big fat greasy bombshell that in their store, the chicken and fish oil hadn't been replaced in four entire months. Let that sink in. The issue here isn't just that the oil is old, but also that when the oil is left that long, it gets disgusting — the worker described a "brown foam" rising to the top of the fryer baskets every time something new goes in. That not only sounds unappetizing, it sounds downright unhygienic. So honestly, letting fryer oil sit that long might be up there with some of the biggest mistakes in McDonald's history.

Now, according to those in the know, the oil used for fries is given a much more decent rotation schedule when compared to the chicken and fish oils. This is probably because the oil used for McDonald's world-famous french fries has be changed more frequently because it's used most often. But for slightly less popular items like chicken patties or fish fillets, the oil is left to hang out for much longer.

The worst part is, this isn't even against any rules. There are no national laws saying how often oil has to be changed, so if a restaurant isn't using a ton of chicken or fish, they're totally within their rights to stretch it out and just keep filtering it daily. It's a fully discretional "depending on volume" kind of system, determined by each individual restaurant manager. So if people aren't ordering a lot of McNuggets, the oil just sits there marinating over time. Which means yes, one of the things you didn't know about your Filet-O-Fish is that it might have been fried in oil older than your last situationship. Yikes.