Chicken – Deep frying without schnitzels sticking to each other

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

It is not "food color" in the conventional sense. McDonald's techniques are based on something the 'home cook' can rarely achieve, consistency. Their friers are designed to maintain exactly the same temperature (375F, if I recall correctly). The typical home frier drops 20-30F as soon as food is added, the McMachines have the kind of heating elements that don't do that. The coating is milled and applied to create a consistent coating and they are cooked for EXACTLY the right amount of time, every time. It is interesting to actually sit and listen to what is going on in McKitchen, military drill teams lack the precision that McD's instills into their burger flippers.