Pressure Cooking Is a Science Cooking Is an Art
In a world of modernist cuisine, sous vide baths and microwave ovens, pressure cookers feel similar a throw-back to the past. However they deserve a special place in the kitchen, especially when energy efficiency, speed or tenderness matters.
But why does a force per unit area cooker faster than chop-chop steaming food in a covered pot? For a applied science that goes dorsum almost three centuries-- surprisingly few explanations for how force per unit area cooking works are correct.
At some level, a pot of steaming h2o and a force per unit area cooker are pretty similar. If primed with a small-scale amount of water, flavors concentrate in a pool of jus. Both devices are saunas delivering 100% humidity, which helps break down tough meat collagen into glace gelatin. Both take reward of the enormous latent heat free energy steam deposits on cool nutrient. It's the same reason you can place your hand in a 250F oven and experience comfortably warm, while your hand to a higher place a steaming pot of h2o apace scalds. But the latent heat per molecule of steam in a stove pot or in a pressure cooker is nearly constant. So latent heat is non the source a pressure cooker'south 50-100% faster speeds.
Which begs the question- how does a pressure cooker work?
A pressure cooker is nothing more than a sealed chamber, fitted with a safe valve. The pressure rises equally water heats on the stove, turns into steam, and the trapped steam molecules move faster and faster. Raising the internal pressure. Depending on the setting of the cooker's safety valve, the pressure vents and plateaus at around twice atmospheric pressure1.
Water normally boils at 212F at sea level (east.yard. i atm.). But, within a sealed container, pressurized steam molecules constantly impinge on the liquid'due south surface, forcing-back liquid water trying to evaporate. All of which suppresses boiling, until rise temperatures propel water molecules by the barrage of incoming steam. At two atmospheres of pressure, the evaporation and venting rates come into equilibrium, and the boiling temperature increases by 38F to 250F.
So-- are higher pressures, or higher temperatures, or both responsible for the faster cooking speed?
Many people claim high pressures "strength" braising liquids into the food, so they cook faster. Just this assertion is quite muddleheaded, as we discuss more fully in an article on vacuum marination.
Nearly all foods are dense with liquid, protein and carbs. No space for steam to enter.
Nor can the steam pry open up nutrient. Steam force per unit area (known as hydrostatic pressure) surrounds and squeezes each piece uniformly. Any attempt to push button steam in at say a crevice in a piece of carrot, is verbal countered past hydrostatic pressure level forcing the carrot's crack closed. A collision.
Food compresses VERY slightly until the force per unit area inside matches the hydrostatic pressure outside. Any liquids within the food won't squirt out, because they are pushed on equally from all directions. It takes a pressure Departure to brand things motility, and there is no pressure level difference beyond the food. There is no "out" direction.
If food contained pockets of air, or was highly compressible similar a sponge, it might compress nether force per unit area, and when the cooker is vented, expand and suck in a bit of liquid. But few foods are that compressible. People (intelligent hunks of meat) aren't that compressible either- when you swim down fifteen feet (near half atmospheric pressure level, typical of an electric pressure cookers), your capillaries don't burst, your eyeballs don't pop out, and even the air in your lungs compresses, matching the external water pressure level. In one case the pressures equalize, which is almost instantaneous, non much happens.
Pressure is Non the caption.
As to temperature, it is true 250F is eighteen% higher than 212F. Simply the Fahrenheit scale is based on setting 32F equally the freezing point of water - an capricious option. Its similar claiming yous're six human foot tall because yous are standing on a stool. The scientific scale for temperatures sets zero to the absence of all physical motion, not to the freezing bespeak of water. Known as the Kelvin scale, h2o boils at 373K, and two atm steam reaches 394K, or an increase of half dozen%. A pretty modest thermal advantagetwo.
No, the real reason force per unit area cookers melt faster is DENSITY. At two atmospheres (retrieve your platonic gas police from high school), steam contains twice as many water molecules as the air over a pot of steaming water. Depositing twice every bit much latent heat every 2nd to the food. And, roughly speaking, cooking up to twice equally fast.
Not temperature. Not pressure. Just density.
Boosted articles on kitchen science can exist plant Hither.
Or follow me on twitter for (very occasional) alerts of new food science postings at @KitSci
In the practice of all-things barbecue, we appreciate the support and conversations with Meathead at AmazingRibs.com, Sterling at BigPoppaSmokers, along with numerous competition pitmasters and backyard chefs.
1 As fans of Mythbusters appreciate, high pressure steam in a sealed container is a recipe for a ballistic missile. Not beef stew. Then abode pressure cookers are limited past a safety valve (and good sense) to under two atmospheres of pressure. Hither, every bit throughout this commodity, I reference pressure to a vacuum. In other words, the pressure inside the cooker is one atmosphere greater than outside. And since outside is at ane atmosphere in a higher place vacuum by definition, the ABSOLUTE pressure within is two atmospheres.
2 In that location are reasons other than speed to prefer 240F over 212F. For example, some microbes, like botulism, shrug off humid water. To kill botulism bacteria, 250F for over 30 minutes is required. This is why people pressure level-melt canning jars to preserve foods that are consumed without reheating, or are not acidic. The high temperatures besides accelerate browning reactions, destroying enzymes that might lead to rotting or mushiness, and then on.
Of course, chemistry as well plays a function. Many chemical reactions speed up exponentially with temperature, so 10 extra degrees can have a disproportionate effect. And, reaction rates can "cross". At 190F rice might cook faster than beans, and 230F beans faster than rice. It's nearly impossible to offer a general rule. Still, most pressure cooker recipes speed upwards by a factor of ii, at about four. Vapor pressure is the i common cistron.
Contact Greg Blonder by email here - Modified 18-carat Ideas, LLC.
Source: https://genuineideas.com/ArticlesIndex/pressurecooker.html
0 Response to "Pressure Cooking Is a Science Cooking Is an Art"
Postar um comentário