Pressure buying
Few cooking appliances have been as significant to the worldwide development of popular catering as the pressure fryer, despite the trained chefs rarely, if ever, operate , but .
The models on offer today are descended from the cooking method which "Colonel" Harland Saunders discovered in his restaurant in Corbin, Kentucky back in 1939.
By frying breaded portions of chicken under pressure, he discovered a way of perking up the succulence and flavour of an otherwise bland meat. It proved so popular that he soon started selling franchises for his Kentucky Fried Chicken - and the rest, as they say, is history.
Although indispensable to fast food caterers, pressure fryers are still a rarity in mainstream restaurant kitchens - even in banqueting. High cost is one deterrent. A pressure fryer able to cook four portion-cut chickens (four "heads" in fast food parlance, which equates to 36 portions) costs about £5,000-£8,000. That's at least three or four times the cost of a large conventional open fryer.
What difference does pressure make? When the substantial lid of a pressure fryer is screwed down to make the fry kettle air-tight, relative pressure quickly builds up to about 14psi (lbs per sq inch).
This has two effects. First, food retains more of its natural juices, whereas in open frying moisture quickly escapes through the oil in the form of steam and the meat can quickly become tough and dry.
Turning up the heat
At the same time, the food reaches a higher internal temperature (approximately 120ºC against the 100ºC which occurs in conventional frying). This also has two effects. Firstly, it results in faster cooking speed (about 12mins per chicken portion against 20mins in an open fryer) giving a higher output per hour at lower energy use. Second, it gives a more moist product with higher retention of both weight and nutrients.
The cooked product should also be less greasy, says John Robinson, field sales manager of Servequip, which sells the Henny Penny range of pressure fryers as used at UK branches of the KFC chain.
"You might think the pressure would force the fat into the chicken, but the reverse is true. The fat can't get into the chicken because the moisture can't get out," he adds.
Exact percentage measurements of the difference are made difficult by the many variables - frozen, semi-thawed, thawed or fresh food, state of the oil and relative loading speed - but a generally accepted claim for oil ingress is 4% on pressure-fried chicken against 10% on the same product fried conventionally.
Another advantage claimed for pressure frying is that there is less flavour transfer because less moisture gets into the oil. But pressure frying is only considered feasible if the frying medium is filtered frequently, especially where, as is usually the case, breaded foods are cooked in large quantities. Most of the pressure fryer suppliers recommend filtering after two or three cooks and some operators insist that staff do it after every cook cycle.
This requirement, and the need for a toughened construction appropriate to pressure cooking, contributes to the relatively high cost of pressure fryers. Most top-end models have the option of a built-in system where the oil is drained from the tank, passed through a mesh and then pumped back in again, taking three to four minutes.
Aside from filtering improvements, the main design innovation on pressure fryers in recent years has been computer control. This option is now available on most full-size pressure fryers on the UK market. Such units allow a variety of cook programs to be entered.
Computer control, which can add up to £800-£900 on to the cost of the fryer, comes into its own when a recipe demands a change of temperature during cooking. The latter occurs with so-called "soft finish" fried chicken, the generally preferred version in the UK, where it is typical to start cooking at a high temperature of around 375ºF and then reduce to about 275ºF. A probe in the fry tank tells the computer not just the temperature of the oil but also the rate at which it changes.
The pressurised operation means safety looms large for most pressure fryer operators. A Henny Penny fryer, for instance, has four lines of defence. It has a lid which cannot be opened accidentally once the fryer is under pressure and a dead-weight valve which prevents pressure rising above 10-12psi. Should this valve jam, a secondary safety valve blows at 14psi. Should that also fail, the rubber around the lid gasket is designed to distort at 18psi, venting the chamber.
Hopefully, such a sequence would never happen but an operator neglecting to service his fryer regularly could eventually encounter problems.
British manufacturer Pandet uses different safeguards. On Pandet's fryers, a spring in the lid flexes if pressure goes too high, letting steam out, but directing it away from the operator.
