Fryers are available with a variety of fry pot styles. Some commercial fryers have a “cold zone” at the bottom of the fry pot. This is where larger food particles sink and the lower temperature keeps them from burning and tainting the oil. A tube-style fry pot has a large cold zone because the tubes are slightly above the bottom of the vat, leaving generous space for cooler oil and crumbs. This is particularly useful for cooking heavily breaded foods (such as a blooming onion). A tube-style fry pot is more difficult to clean than an open fry pot, but the tubes allow easy access to the heat source. Tube fryers are often a little less expensive than their open fry pot counterparts. Open fry pots have an external heat source, which makes them easier to clean and affords better access to the oil, but they generally offer a smaller cold zone, so food particles that sink could scorch and pollute the flavor of the oil. However, these fryers work very well for lightly breaded foods. Flat-bottomed restaurant fryers—another type of open frypot fryer—can also be difficult to clean and have no cold zone, but they are highly effective for frying dough (such as donuts or funnel cakes). Flat-bottom fryer pots may also be used with a batter trapping insert that keeps loose batter from quickly scorching on the bottom where heat is normally applied. A batter trap can also help keep loose batter from being stirred up in the oil and adhering to subsequent batches of food in order to make foods taste better and the cooking oil lasts longer