Think of the word convert as meaning change, whether it is a person who adopts a new belief, or a changing action, such as when you convert dollars into euros. Many times we can catch a word's meaning by looking at its origins. In this case, the Latin con means around, while vertere means turn..
Maple sap runs best when it freezes at night (e.g. in the high 20-degrees Farenheit range) and then warms up above freezing the next day (in the range of 40-degrees Farenheit and hotter). If it stays warm at night and warm during the day or if it freezes at night but barely goes above freezing the next day, sap does not flow as well or hardly at all.
The boilers boil away most of the water found in the sap. 40L of sap is equal to 1L of maple syrup. when enough water is boiled off, they remove the soon-to-be maple syrup. a material such as egg whites or milk will be poured in the syrup to form impurities, which are later filtered out of the maple syrup.