Heat Transfer, Conduction, Convection, Radiation and Microwave Cooking

Posted by PITHOCRATES - September 4th, 2013

Technology 101

At the Atomic Level Vibrating Atoms create Heat

We make life comfortable and livable by transferring heat.  And by preventing the transfer of heat.  In fact, once we discovered how to make fire our understanding of heat transfer began and led to the modern life we know today.

At the atomic level heat is energy.  Vibrating atoms.  With electrons swirling around and jumping from one atom to another.  The more these atoms do this the hotter something is.  There is little atomic motion in ice.  And ice is very cold.  While there is a lot of motion in a pot of boiling water.  Which is why boiling water is very hot.

How do we get a pot of water to boil?  By transferring heat from a heat source.  A gas or electric burner.  This heat source is in contract with the pot.  The heat source agitates the atoms in the pot.  They begin to vibrate.  Causing the pot to heat up.  The water is in contact with the pot.  The agitated atoms in the pot agitate the atoms in the water.  Heating them up.  Giving us boiling water to cook with.  Or to make a winter’s day pleasant indoor.

Fin-Tube Heaters create a Rising Convection Current of Warm Air to Counter a Falling Cold Draft

If you touch a single-pane window in the winter in your house it feels very cold.  Cold outside air is in contact with the glass of the window.  Which slows the movement of the atoms.  Bringing the temperature down.  This cold temperature doesn’t conduct into the house.  The heat conducts out of the house.  Because there is no such thing as cold.  As cold is just the absence of heat.

The warm air inside the house comes in contact with the cold window.  Transferring heat from the air to the window.  The atoms in the air slow down.  The air cools down.  And falls.  This is the draft you feel at a closed window.  Cold air is heavier than warm air.  Which is why hot air rises.  And cold air falls.  As the cold air falls it pulls warmer air down in a draft.  Cooling it off.  Creating a convection current.

To keep buildings comfortable in the winter engineers design hot-water fin-tube heaters under each exterior window.  Gas burners heat up water piping inside a boiler.  The heat from the fire transfers heat to the boiler tubes.  Which transfers it to the water inside the tubes.  We then pump this heating hot water throughout the building.  As it enters a fin-tube heater under a window the hot water transfers heat to the heating hot water piping.  Attached to this piping are fins.  The heat transfers from the pipe to the fins.  Which heats the air in contact with these fins.  Hot air rises up and ‘washes’ the cold windows with warm air.  As it rises it pulls colder air up from the floor and through the heated fins.  Creating a convection current of warm air rising up to counter the falling cold draft.

Microwave Cooking won’t Sear Beef or Caramelize Onions like Conductive or Radiation Cooking

If you’ve ever waited for a ride outside an airport terminal on a cold winter’s day you’ve probably appreciated another type of heat transfer.  Radiation.  Outdoor curbside is open to the elements.  So you can’t heat the space.  Because there is no space.  Just a whole lot of outdoors.  But if you stand underneath a heater you feel toasty warm.  These are radiators.  A gas-fired or electric heating element that gets very, very hot.  So hot that energy radiates off of it.  Warming anything underneath it.  But if you step out from underneath you will feel cold.  It’s the same sitting around a campfire.  If you’re cold and wet you can sit by the fire and warm up in the fire’s radiation.  Move away from the fire, though, and you’re just cold and wet.

We use all these methods of heat transfer to cook our food.  Making life livable.  And enjoyable.  When we pan-fry we use conduction heating.  Transferring the heat from the burner to the pan to the food.  When we bake we use convection heating.  Transferring the heat from the burner to heat the air in the oven.  Which heats our food.  When we use the broiler we use radiation heating.  Using electric heating elements that glow red-hot, radiating energy into the food underneath them.  A convection oven adds a fan to an oven.  To blow heated air around our food.  Decreasing cooking time.

There’s one other cooking method.  One that is very common in many restaurants.  And in most homes.  But real chefs rarely use this method.  Microwaving.  With a microwave oven.  They’re great, convenient and fast but fine cooking isn’t about speed.  It’s about layering flavors and seasoning.  Which takes time.  Which you don’t get a lot of when a microwave begins vibrating the atoms in the water molecules in your food.   Which is how microwaves cook.  Cooking by vibrating atoms in your food brings temperatures up to serving temperatures.  Unlike conduction heating such as in pan-frying where we bring much higher temperatures into contact with our food.  Allowing us to sear beef and caramelize onions.  Something you can’t do in a microwave oven.  Which is why real chefs don’t use them.

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Cowboy Coffee, Percolator and Electric Drip Coffee Maker

Posted by PITHOCRATES - June 26th, 2013

Technology 101

Done Right Cowboy Coffee is one of the Finest Cups of Coffee you will ever Have

The British love their tea.  They love it so much they call lunch ‘tea’ in Britain.  Their world stops when it’s time for tea.  As they place a kettle of boiled water, cups on saucers, milk, sugar and lemon on a tray and bring it in to a warm gathering of friends and colleagues.  Then prim and proper British gentlemen and ladies prepare their tea.  Sit with good posture.  And sip their tea with pinky extended.

The British brought their treasured tea to the New World.  And British Americans continued the tradition.  Until the Boston Tea Party and the Revolutionary War.  And the War of 1812.  Interrupting the British-controlled tea trade.  It was these events and a general dislike of all things British during those turbulent times that changed American tea drinkers into coffee drinkers.  Something we didn’t have to do with such dainty British manners.  As Americans were not quite as prim and proper.  Or refined.  Americans were more rough and tumble.  As epitomized by the American cowboy.  (Caution: The following clip from Mel Brooks’ Blazing Saddles has crude and sophomoric humor featuring cowboys breaking wind.)

Not quite the refined British tea.  Note the beverage they were drinking.  Hanging on the tripod over the campfire is a large coffee pot.  Where these cowboys make ‘cowboy coffee’.  Course coffee grounds go into the coffee pot.  Fill with water.  Place over campfire.  Heat water to just below a boil.  Carefully pour out coffee without stirring up coffee grounds from the bottom of the pot.  Enjoy.  Done right and it will be one of the finest cups of coffee you will ever have.  And something that really hits the spot on the trail after a long hard day.  Though not as refined as British tea it is just as comforting.

A Common Complaint about Coffee Percolators was that they made Bitter Coffee

Cowboy coffee can be delicious.  Or it can be horrible.  For temperature and brew time are critical in making coffee.  As well as the proportion of coffee grounds to water.  The proper temperature to brew coffee is between 195 and 205 degrees Fahrenheit.  This will release the oils from the coffee beans.  But if the temperature reaches boiling the coffee will be bitter.  So for good cowboy coffee you needed to put in just the right amount of ground coffee beans with just the right amount of water.  And keep the water just below the boiling point.  And once the coffee brewed you needed to drink it.  For sitting on the heat too long will just evaporate the water away leaving a strong, bitter, muddy water.

Around the time of the American Civil War we started using coffee percolators.  Where instead of placing ground coffee beans in a pot of water we dripped water through a basket that contained the ground coffee beans above the water.  In the center of this basket was a tube that went from the bottom of the percolator to the top.  We placed this percolator onto the stove.  This heated the water.  As the temperature rose the water expanded.  The water in the narrow tube expanded so much in that small tube that it pushed all the way up and out at the top of the tube.  And dripped onto the top of the coffee grounds.  Dripped through them.  And out the bottom into the heated water below.

This cycle continued over and over until the water in the pot started getting darker.  The top of the pot, above the tube, was a glass knob.  Which we could see through.  And observe the color of the water percolating up from the bottom of the pot.  When it turned to the appropriate ‘coffee color’ we removed the percolator form the stove.  And served the brewed coffee.  Using a stove, though, made it easy to boil the water.  Which would make the coffee bitter.  A common complaint about percolators.  As well as some coffee grounds that passed through the basket into the pot.  And poured into our cup.  But some preferred the full robust flavor percolating gave.  Even if it was bitter from overheating the water.

A Quality Electric Drip Coffee Maker can pour 195-205 Degree Water over Coffee Grounds in under 8 Minutes

Thanks to Nikola Tesla and his AC power Americans soon had electricity in their homes.  And a whole sort of electric appliances to use with that electricity.  Including an electric coffee percolator.  Which reduced the chances of boiling the water by controlling the temperature of the water.  There was a temperature sensor that shut off the heating element if the water temperate approached boiling.  When the temperature fell below the optimum temperature range (195-205 degrees Fahrenheit) the temperature sensor turned the heating element back on.  Making it easier to make a good cup of coffee in the home.  Until the Seventies came around.  And the electric drip coffee maker.

The electric drip coffee maker is a staple of most American kitchens today.  It is now the way we make coffee at home.  By heating water to an appropriate temperature and dripping that heated water through a coffee filter full of ground coffee beans.  Once brewed the coffee drips into a carafe.  Which sits on a warming plate.  Unlike the percolator which sent brewed coffee back through the basket holding the coffee grounds over and over again.  The electric drip coffee maker has a reservoir of cold water.  At the bottom of this reservoir is a tube with a check-valve.  Which allows water to flow only one way through the valve.  Past this check-valve is a horseshoe-shaped metal tube.  Attached to this metal tube is a heating element.  Past this metal tube is a hose that runs up to the top of the coffee maker.  And out through a spray-head onto the coffee grounds.

As the heating element heats the water in the metal tube it expands.  Because it can’t go back into the reservoir thanks to that check-valve the water rises up the tube and out through the spray-head.  As the water moves up the tube the siphon it creates pulls water from the reservoir through the check-valve into the metal tube.  When it heats and expands it rises up the tube to the drip-head.  And this cycle repeats again and again until the water reservoir is empty.  A temperature sensor turns the heating element on and off to maintain the proper water temperature.  Like the electric coffee percolator.  But the addition of a coffee filter prevents any grounds from ending up in our cup.  Also, a well-designed drip coffee maker can pour this properly heated water over the coffee grounds in under 8 minutes.  Another key to making an excellent cup of coffee.  Other advances include a timer.  Allowing us to set up the drip coffee maker the night before so we can have a freshly brewed cup of coffee first thing in the morning.  So we can grab a cup on the way out the door.  American style.  In a hurry.  Unlike the British.  Who stop the world when it’s time for tea.

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