Behind everything fried (and really…what hasn’t been fried?) are a few tasty food science secrets.
Oil selection: Some oils are better for deep frying than others. Most of us go for a neutral-tasting oil (canola, vegetable, safflower, etc) because we like to taste the food, not the oil. Additionally, oils have different smoke points (the temp at which the oil begins to degrade), and for frying, an oil with a high smoke point is required. (Extra virgin olive oil is not a good choice for frying.)
Oil temperature: Get it hot! When food hits the hot oil, the inner moisture turns into steam and escapes. This escaping steam contributes to puffed batters, tender (un-soggy) centers, and crisp golden coatings. Remember not to over-crowd your fryer – it may drop the temp.
Residence time: Monitor how long your food stays in the fryer. If you don’t fry long enough, you’ll risk undercooked food – not a big deal for cheese balls, but it’s a food safety concern for chicken. If you fry too long, the result may be oil-logged insides. (I’m usually drooling by this time…so over-fried food isn’t usually much of a risk.)
Got leftovers? (I never do.) Stick them in the oven to re-crisp. A zap in the microwave will cause your previously crispy food to sog.
A Food Science tid-bite: Oil can be expensive, so many people try to re-use frying oil. But, when exposed to heat, light, and oxygen, oils are highly susceptible to rancidity. When the oil darkens and develops off flavor (and aromas) throw it out.
Source: Amy Christine Brown. Understanding Food: Principles and Preparation. Thomson Learning Inc, 2008.