HEAT TRANSFER WATER

HEAT Rapid movement of molecules Rapid movement of molecules Kinetic energy Kinetic energy Measured by thermometer = temperature Measured by thermometer = temperature Collision of molecules transfers heat Collision of molecules transfers heat Cooking is transfer of heat or heat produced in food Cooking is transfer of heat or heat produced in food

EFFECT OF COOKING Increase palatability Increase palatability Decrease or destroy pathogens Decrease or destroy pathogens Reduce spoilage organisms Reduce spoilage organisms Improve digestibility Improve digestibility Change flavor, texture, color of food Change flavor, texture, color of food Extend shelf life Extend shelf life Rehydrate Rehydrate

CHANGE OF STATE Change from solid to liquid, liquid to gas Change from solid to liquid, liquid to gas Involves energy Involves energy

SOLID STATE OF WATER Ice Ice Molecules do not move freely Molecules do not move freely Ice is lowest energy state, steam the highest Ice is lowest energy state, steam the highest Energy is lost as water cools Energy is lost as water cools Bond angle increases as water cools causing increase in volume – significant in freezing of food – coordination number Bond angle increases as water cools causing increase in volume – significant in freezing of food – coordination number Ice less dense than water Ice less dense than water

GASEOUS STATE OF WATER Water vapor Water vapor Molecules move freely Molecules move freely Vaporize at room temperature  vapor pressure Vaporize at room temperature  vapor pressure Apply heat  increases vapor pressure Apply heat  increases vapor pressure Boiling point is temperature at which vapor pressure just exceeds atmospheric pressure Boiling point is temperature at which vapor pressure just exceeds atmospheric pressure Atmospheric pressure decreases with increase in altitude Atmospheric pressure decreases with increase in altitude High altitudes  vapor pressure is high  lower temperature for boiling  cook foods longer High altitudes  vapor pressure is high  lower temperature for boiling  cook foods longer Boiling point at sea level F = C Boiling point at sea level F = C

USE OF ATMOSPHERIC PRESSURE PRESSURE COOKER OR CANNER- atmospheric pressure increased by steam  PRESSURE COOKER OR CANNER- atmospheric pressure increased by steam  more energy needed to make water boil more energy needed to make water boil Higher temperature = faster cooking Higher temperature = faster cooking VACUUM PAN - make juice concentrates or preserves VACUUM PAN - make juice concentrates or preserves Lowered pressure-less energy, water boils at lower temperature  evaporation occurs quickly  less loss of volatile flavors Lowered pressure-less energy, water boils at lower temperature  evaporation occurs quickly  less loss of volatile flavors

LATENT HEAT Heat to change from one state to another without changing temperature as measured by thermometer Heat to change from one state to another without changing temperature as measured by thermometer Heat absorbed changing from solid to liquid – latent heat of fusion Heat absorbed changing from solid to liquid – latent heat of fusion Heat released changing from liquid to solid – latent heat of solidification Heat released changing from liquid to solid – latent heat of solidification Heat absorbed changing from liquid to gas – latent heat of vaporization Heat absorbed changing from liquid to gas – latent heat of vaporization Heat absorbed changing from gas to liquid – latent heat of condensation Heat absorbed changing from gas to liquid – latent heat of condensation

TYPES OF HEAT TRANSFER

CONDUCTION Kinetic energy transmitted from molecule to molecule Kinetic energy transmitted from molecule to molecule Slow method Slow method Liquids heat faster than solids or gases Liquids heat faster than solids or gases Metal good conductor Metal good conductor All cooking involves some conduction All cooking involves some conduction

CONVECTION Energy via air, water, liquid, fat Energy via air, water, liquid, fat Transfer of heat due to currents of warmer vs colder air or liquid Transfer of heat due to currents of warmer vs colder air or liquid Sets up circular flow to keep temperature even Sets up circular flow to keep temperature even More rapid than conduction - slower than radiation More rapid than conduction - slower than radiation Boiling, deep fat frying - mostly conduction Boiling, deep fat frying - mostly conduction Using fans to disperse heat increases convection currents  reduce temperature and time Using fans to disperse heat increases convection currents  reduce temperature and time

RADIATION Energy goes directly from source to object Energy goes directly from source to object Rapid method of heating Rapid method of heating Important in baking, roasting, broiling Important in baking, roasting, broiling Clear glass best for radiation transmitter Clear glass best for radiation transmitter Shiny metal worst transmitter Shiny metal worst transmitter

HEAT TRANSFER MEDIA

AIR Medium in baking, roasting, broiling Medium in baking, roasting, broiling Generally dry heat cooking methods Generally dry heat cooking methods Air is heated  heat transferred to food Air is heated  heat transferred to food Dry heat  toughens meat Dry heat  toughens meat Uses conduction, convection, radiation Uses conduction, convection, radiation

WATER Boiling, simmering, poaching, braising, stewing Boiling, simmering, poaching, braising, stewing Moist heat-tenderizes if not overdone Moist heat-tenderizes if not overdone Uses mainly conduction and convection Uses mainly conduction and convection Cooks faster than air Cooks faster than air Limits to temperature rising – highest boiling point of water (212 0 f) Limits to temperature rising – highest boiling point of water (212 0 f)

STEAM Moist heat method of cooking Moist heat method of cooking Over boiling water or wrapped and baked Over boiling water or wrapped and baked Pressure canner uses steam  containment of steam raises vapor pressure  increase in boiling point of water Pressure canner uses steam  containment of steam raises vapor pressure  increase in boiling point of water Cooking very rapid Cooking very rapid

FAT Only medium which is a food that becomes part of the food = ++ calories Only medium which is a food that becomes part of the food = ++ calories Cooks at higher temperatures than water Cooks at higher temperatures than water Cooks faster than water Cooks faster than water Case hardening – hard crisp case on exterior, interior cooked by steam Case hardening – hard crisp case on exterior, interior cooked by steam Pressure frying – steam formed gets hotter Pressure frying – steam formed gets hotter Saute – lower temperature, less crisping Saute – lower temperature, less crisping