How to cool down cooking oil after using it in a deep fryer

I would not reuse that oil. The frying-oil reuse that occurs in fast food chains is reuse for the same day or over just a few days. They also store it properly and not just sitting exposed in the fryer.

justkt is correct that more saturated fats are less sensitive to breakdown, this is why bacon grease can be kept for a rather long time.

Three factors play a significant role in oil degradation:

Oxidation

Any contact with air causes oxidation in oil. High temperatures, metal alloys, surface exposure, and even UV light act as catalysts to this reaction.

Hydrolysis

When water interacts with oil it causes it to taste tainted or acidic. This is exacerbated by high temperatures, heating/cooling cycles, and oxidation products.

Polymerizaton

When frying oil deteriorates, the resulting products form both volatile (or reactive) and non-volatile compounds. Non-volatile compounds remain within the frying oil, and can produce polymerization at frying oil temperatures above 200°C (390 F) or in isolated hot spots within the frying system. These molecules bond together to form large, different-sized clusters that accumulate on the oil’s surface. Since they don’t dissolve, they cause foaming; trapping air under the oil, and increase the possibility of hydrolysis.

Given all these, the best environment for any oil is an cold, dark, airtight place. Cold temperatures may cause clouding, but this is not a cause for worry.

Source:

http://www.heatandcontrol.com/technical%20articles/Maximizing%20Cooking%20Oil%20Life.pdf

Deep frying is certainly an easier way to get things crispy, but there are things you can do to get crispy batter without it.

First off is the bread crumbs. Ideally the bread should be relatively stale and therefore dry. If you blitz your own breadcrumbs, leave them out for a few hours to thoroughly dry out before you pane. You can also try using panko, which are pre-packed Japanese breadcrumbs that are very crispy. You can usually find them in supermarkets these days.

The other thing you can do is double-crumb the chicken, so flour, egg, breadcrumbs, egg, breadcrumbs. This double layer of crumb should make for a really crunchy crust.

Finally, you can pseudo-deep fry using a wok. Rather than a full pan of hot oil, just put an inch of oil in a wok and fry in that: safer and less waste. A good way of knowing when the oil is hot enough is to use a wooden chopstick. Simply put the tip into the oil and if bubbles immediately gather around it, the oil's hot enough.

Set your oven to about 120 degrees F/50 degrees C, pop a plate with some kitchen paper on it in there, and fry in batches, placing the chicken on the plate while do you the rest.

If you use this method, you could try a tempura style batter. Take 100ml of chilled soda water and mix with 140g of self-raising flour and mix well. Dust your chicken with cornflour (cornstarch), then into the batter and straight into the oil. Turn a few times to ensure even cooking - when the batter is a nice golden brown it should be done, about 5-6 minutes.