Snow is found in the forests from New England and Quebec to Ontario, Wisconsin and Minnesota, but cold nights together with warm days mean the sap is running or will soon. The best sap flows occur when a frosty night is followed by a sunny day with a temperature in the 40s or higher. Late afternoon is a good time to collect the day’s flow. In southern Minnesota, the best flows tend to come during March and the first few days of April, at which point leaf buds swell and the sap becomes bitter.

The art of tapping maples and making syrup and sugar was developed by American Indians and passed on to early European settlers. Before the 1860s, maple products were the principal sweetening material used in the United States, and today we continue to enjoy their unique flavor.

The sap will flow from any wound in the sapwood — a hole bored into the tree or a broken twig. Sugar maples, black maples and box elders, also known as ash-leaved maples, are the best for tapping. Red maples and silver maples can also be tapped, but their sap is less sweet. A forest of many maple trees together is called a sugarbush. Maples are tapped using a carpenter’s brace with a three-eighths of an inch bit. Trunks smaller than 10 inches should not be tapped. Holes 2 inches deep are bored into the tree trunk about 3 feet above ground. A small metal or wooden tube called a spile is inserted into the hole and tapped lightly with a hammer so it fits snugly. The spile supports the container and carries sap into it. Old wooden buckets and metal pails have been largely replaced by plastic bags and tubing.

Maple syrup is made by boiling the maple sap in a shallow pan until it contains a high percentage of sugar. When a candy thermometer reads 7 degrees above the boiling point of water, the syrup is ready to be strained and bottled. Usually 30 to 40 gallons of sap are required to produce a single gallon of syrup. The amount depends on the sugar content of the sap, which is mostly water.

Jim Gilbert’s Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. His observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.