Frying - Oil foams

You are right that the moisture in the potatoes are what's causing the oil to 'foam'. If you don't dry your potatoes sufficiently they can quite easily cause the oil to 'boil' explosively out of the frier; this is why you never pour water on a deep-fat pan fire.

There are various ways to dry out your chips/straws, but one of the most effective ways to is to lay them out on a tray or plate and put them, uncovered, in the fridge for a couple of hours, making sure there are no strong odours in there first. Not only will this prevent too much foaming, it will result in really crisp chips!

The foaming is the moisture in your fries boiling off, with the starch in the fries making it foamier. You can solve this problem by blanching them briefly in boiling water to remove some excess starch, then pre-frying them at a much lower temperature to remove some moisture (draining off excess oil).

The pre-frying keeps the fries from getting soggy as fast (less core moisture), lets them fry faster, reduces foaming (less moisture to remove), AND (bonus) helps achieve better browning. It's one of the secret tricks that restaurants use (including the one I work for).

I have found this question to be one of the most difficult to get an answer to. I share your dilemma. The clue in your question, often ignored, is that you have been using your oil "for some time now". I agree it does not occur with new oil. Replacing it will clearly solve your problem but does not explain... why! The best I can offer is that the molecular structure of the oil must alter with use, perhaps combining with water. Oil is hydrophobic and works by driving water out of the food. This is observed by foaming even with new oil (but to a lesser extent). Why used oil should foam more readily and take longer to cook food remains a mystery to me, But it does! Like you, my much used oil appears clean and odorless as I never use it for frying crumbed, breaded or flour-dredged food. I am not easily persuaded that it may be harmful to use either.

Regarding Coconut oil: I decided to give this a try in my cheapie fryer, because I had done some research into the "least foaming" oil; the longest lasting oil (for regular draining and reuse), and the supposedly healthiest oil to use anyway. What I discovered was, that Coconut oil does seem more prone to foaming, and I have had a couple of incidents of it spewing out over the top of the fryer - whether lid closed or open. I got lots of kitchen paper ready just as a precaution before I used it, but it is still a lot to clean up, as well as being potentially dangerous - firewise. While other types of oil are noted for not foaming, in my case it was usually when using frozen fries that this occurred. Having said that, I found that if I turned the fryer temperature down to 160c at the beginning, left the lid open, and let it foam if necessary for a bit - the foaming then died down, and I was able then to turn it back up to 170c (190c at the end for the "double frying" if desired.) Remember that this was when using the Coconut oil. I get the impression though, that Coconut oil (even if healthier) is not the best/safest oil to use in a fryer like mine. However, one of the reasons for the choice in the first place is that Coconut oil is supposed to be useable and reusable for a very long time, without going off or "rancid". The problem with using frozen "fries" is that the ice on them is water (albeit frozen) and I think this is why THEY are inclined to cause foaming. It might be different with different fryers/types of fryer, but there's an expirimental aspect to such an exercise. The leaving up of the lid in the first place, and the lower temperature at the start seems to work, but the Coconut oil certainly gets pretty near the rim before it settles to a safer level. Apart from these discoveries in practice, and keeping to the aforementioned experience with frozen fries, I think I will be going back to a more conventional oil in future.

I discovered after lots of experience in deep frying that after using peanut oil a few times for deep fried chicken strips or turkeys, with perfect results, the oil will begin to breakdown and start to foam. Time for new oil.

It is happening to me as we speak with brand new oil. a mix of about 60 / 40 sunflower and coconut. I figure it must be the starch causing the foam. I dried my french-cut potatoes in the salad spinner beforehand.

I came here looking for an answer. I have been using pure olive oil for frying potato chips without any problem. It cooked well, left no unpleasant odor or taste, handled the high temperature and never foamed. But, I had coconut oil and wanted to switch over to it so I added it to the olive oil and got a surprise. It swelled up from a couple inches of oil to over ten inches of foam. I haven't found any information concerning the foaming of just coconut oil so it must be the mixing of these oils that caused the foaming. I believe the two oils are different enough that their molecular structure won't allow the moisture in the potatoes to purge quickly enough to prevent the retention of bubbles causing the foaming.

I mostly use Sunflower oil for frying, and I will re-use it up to five times before discarding, but only for vegetables or potatoes. The last time I use it I will generally use it for frying some meat dredged in flour because I know it will be the last time.

I only ever get foam when I fry chicken or porkchops, so I'm not sure what causes the foam. With potatoes it will bubble up, but not to the point of foam. Maybe starch? When I am making Fries or chips, I cut the potatoes and soak them in cold water, rinsing twice to get rid of as much of the starch as I can, then drain and pat dry before dropping them in the oil. The thing that might make a difference is that I don't use a dedicated fryer, but a 12" pan on an induction surface with oil at about a 1" depth. Temp I keep at 350F to 375F (170 to 190c) and I will fry them twice for 6 minutes with a 6 minute rest in between. It works with minimal mess for me. Hope this helps!

To reduce and stop foaming buy a Distilling Conditioner on line which is a defoaming agent used in brewing. Put half a teaspoon into the oil, problem solved.