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Comment by tcbawo | Hacker News Reader

It seems that the boiling point and flash point of rosin is quite high, somewhere close to 390 degrees Fahrenheit. So, transferring the heat directly into potato probably has some positive effect on cooking, but I would think cooking potatoes at that temperature in high temp cooking oil would produce a similar effect without toxicity. Giving up reusability seems like a good tradeoff.

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I doubt the rosin is more reusable than cooking oil. Restaurants often reuse the same fry oil for very long periods of time.

Not "very long" no. The oil can be cleaned and reused a few times but even with light use a week is pushing it. Places that do a lot of frying are changing oil every other day, possibly even daily at like a fried chicken place.

I think this is going to depend on the quality of the restaurant and any regulations they're subject to... in any case a week of restaurant use is probably equivalent to a person at home reusing the same oil for years

I've never worked in a jurisdiction where the health code covered this. The oil starts smoking at cooking temperatures and foams and doesn't cook right. The food coming out of it looks and tastes and smells bad.

You also can't go years with it at home even with few uses. After you've fried in it once the oxidation goes much faster even if you don't use it again. Maybe if you freeze it between uses but I've never heard of that.

I intentionally used the words "very long" instead of an exact time specifically to avoid pedantic replies along the lines of "no not actually that long but slightly shorter" because my point was that cooking oil, like rosin, is sometimes reused in some contexts and by some people. Please replace "very long" with whatever exact period of time you think is the longest time the shadiest possible restaurant with awful food might let their cooking oil go for.

I'll admit that I pretty much deserve this, because pointing out that cooking oil can also be reused, was itself a pretty pedantic and pointless thing to mention.

idk why don't you instead just admit you were confidently spouting off about something you know nothing about

I’ve never worked in a restaurant and don’t know how long they keep their oil for. However, I used to engineer commercial biodiesel plants, and am very familiar with exactly how rancid, oxidized, and contaminated with solids used oil from restaurants often is- I’ve seen some truly nasty stuff and don’t eat fried food from restaurants. “food coming out of it looks and tastes and smells bad” is exactly right.

I used to work at McDonald's. The deep fryer oil was filtered and the fryers cleaned every night. You could tell when the oil needed to be changed, it was dark and smokey. 5-7 days was about the limit, we always discarded the oil from at least one fryer every night, and we had 6.

When they switched from beef tallow to vegetable oil, it seemed like they needed to be changed a little more often.

Unsaturated oils are less chemically stable, they oxidize quickly

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