Uses

• This cook used parchment to also help prevent icing from dripping onto the pan, easing clean up.Comstock Images/Comstock/Getty Images
  
  Parchment paper has many uses, and one is to line sheet pans before food is put on and it all goes into the oven. The role of parchment is two-fold. First, it helps to protect the pan from burnt foods and makes it easier to clean. Grease travels under the paper, so parchment doesn't keep it clean, but it does ease clean up. Secondly, parchment prevents sticking. When baking rolls or cookies, a layer of parchment will ensure that nothing sticks to the pan.
  
  

Folding Parchment

• One sheet of parchment will cover an industry-size sheet pan, but many home cookie trays, pans and ovens are smaller. Cut the parchment down to the size of the pan without doubling up. Double layers waste the paper and also create a thick buffer at the bottom of the pan. This buffer will prevent efficient browning and may lead to the interior of goods remaining raw. Also, loose corners may raise in the oven and could burn. Never fold or double-up parchment.
  
  

Re-using Parchment

• This baker is re-using his parchment. Some egg wash dripped on it from the last batch and turned brown, which is ok, but when the paper itself turns brown, time to discard for a new sheet.Steve Baccon/Digital Vision/Getty Images
  
  Often when baking, more than one batch may go into the oven. For example, when making chocolate chip cookies, the dough must be spaced enough to spread out. Therefore, only a portion is on each tray and more than one tray goes into the oven to finish baking all the dough. Parchment may be reused, but it will become brown after prolonged exposure to high heat. As the paper browns, it creates carcinogens, so don't use it after it begins to brown. Also, reused parchment has a higher chance of burning.
  
  

Greasing Parchment

• Convection ovens use a fan at the back to circulate hot air all around the inside. This circulation means that the temperature is quicker to rebound after the oven is opened, easily maintained when the door is closed and therefore can cook the food faster. The fan, however, can blow the parchment around in the oven, sometimes causing it to fold over the top of what is being baked, inhibiting the heat from reaching the product and exposing the paper to excess heat which could cause burning. Some recipes call for greasing parchment for this reason. To grease, rub the pan with butter or use non-stick spray, then put the parchment on top.