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Triple cooked chips (French fries) are made by:

  1. Boiling the chips, then cooling them in the fridge/freezer to remove moisture
  2. Deep frying at a low(ish) temperature, then cooling again as above
  3. Deep frying at a higher temperature

The intermediary cooling steps are for drying and removing water content. How does the fridge/freezer remove water, rather than just changing its temperature/state? Wouldn't, say, sun- or air-drying work better?

  • So the lower temperature makes the water less soluble and then it's easier to drive out by the oil when it's deep fried? – Xophmeister Mar 9 '17 at 16:23
  • @wumpusD'00m if you think that your idea is likely enough to be the answer, please write it up as an answer. If you are so unsure that it is a complete shot in the dark, it is preferable to not confuse people with it. Writing answer suggestions in comments because you are not sure is something we have all been tempted to do, but in the big picture, it is at odds at how the site produces good content, so we mods have to delete them. – rumtscho Mar 9 '17 at 19:31
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The matter here is much more complex than simple "drying out". Starch physics is complicated stuff, and I don't know it in all details, but here is the rough picture.

Starch starts out in tiny granules in the plant. When it is soaked in water and then heated, there is a temperature at which it rapidly turns from a starch suspension (if you had free starch) to a colloid (starch gelatinization). The theory is that these tiny granules burst, but I don't remember if it is proven yet.

At that point, the starch colloid is at its softest. It starts slowly losing water and recrystalizing (starch retrogradation). You can best see it in standard French bread - if you try cutting into it in the first hour after coming out of the oven, you get squished gluey crumb. After that it is soft like cotton for several hours to a day, but gets drier and harder. On the next day, it is already quite dry, and soon after it becomes stone hard.

Just like the gelatinization process, the retrogradation is also temperature dependent. And it happens to work quickest at fridge temperatures. It is slower at warm temperature, and stops when frozen.

So, your goal is not simple dehydration, and other dehydration methods will not really help you much here. You have to stick with what works, and that's temperatures just above freezing.

  • So, in your opinion, it's the physical structure of the starch that facilitates the drying process, by "pushing" the water out to evaporation in the cold air? I presumed also that freezing would have the effect of locking in moisture as ice -- that would melt upon frying -- which perhaps further adds credit to refrigeration over freezing. Anecdotally, however (I tried this over the weekend) the coldness attracts condensation, so -- externally, at least -- the chips are quite wet to the touch. Perhaps "overnight" just isn't enough time... – Xophmeister Mar 13 '17 at 16:18
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    In my opinion, the drying process is a side effect which matters much less than the restructuring of the starch. In anything starch based (potato, bread, cake) the difference between soft, creamy, dry, etc. mouthfeels is not about the absolute amount of water, but the structure of the solids (starch and whatever else is mixed in). This includes the water bound to the basic structure, but once you get the right structure, you have the right amount of water, not the other way round. And if you try to get the right amount of water without paying attention to the starch structure, that won't work. – rumtscho Mar 13 '17 at 16:32
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    The surface dryness is not irrelevant for the frying, because it changes the heat transfer from oil to potato in the first few seconds until the water evaporates, but I forgot what the exact relationship is. So it's relevant for the crust of the potato, but not very much for the inside. – rumtscho Mar 13 '17 at 16:40
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    @Jefromi you are right, I had forgotten about the part in which the chip hits the oil until the OP probed deeper and I realized that my answer is also not complete. Now only if I could remember which source I have read about potato chips (I never deep fry, so I forget such things) to see if wet surface makes them good or bad - it must have been one of the detail obsessive authors, so probably Kenji or Dave Arnold. – rumtscho Mar 13 '17 at 16:53
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    Yup, neither of us covered everything, but between us hopefully we did okay! Just a vote for not bothering to worry too much about exactly how important each factor is. – Cascabel Mar 13 '17 at 16:54
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There are a lot of things going on to change the starches in the potatoes besides drying too; see rumtscho's answer for more on that. However, the drying matters as well, and these are indeed good methods of drying.

Refrigerators and freezers are notoriously good at drying things out. You might've noticed food drying out in your fridge if it wasn't well-covered, and freezer burn is a huge deal.

The air inside fridges and freezers is kept pretty dry, and it's circulating, pretty much ideal conditions for drying. Freezers really need to be pretty dry, since they're trying to prevent frost formation. But fridges are dry too too: the air is only a little above freezing, and the cooling coils are below freezing, so moisture is drawn out. Either way, it's still air-drying, just at a cool temperature.

Hot air is also good at drying things out, but I don't think you actually want the drying stage to further cook your food. Leaving it at warm room temperature with a fan would dry it pretty well too, but then you'd have a food safety issue.

The main alternative would presumably be a dehydrator, running at a bit over 140F, thus keeping things safe while avoiding further cooking. But that wouldn't accomplish the same changes in the starch, and that's not something most people have, so the fridge/freezer seems to make a lot of sense as a common, effective method.

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