Making Maple Syrup with Acer saccharum

As was previously mentioned in the introduction, Sugar Maple trees are the primary source of maple syrup. Maple syrup is one of the oldest naturally made food products in North America dating back to the American Indians when they discovered this sweet product hundreds of years ago. Although the methods used to make maple syrup differ in complexity, they all require the collection of Maple sap and the evaporation of the water to yield the Maple Syrup.

Various species of Maple trees can be tapped for Maple Syrup, but Acer saccharum is tapped most often because its sap contains higher sugar content than most other species. The second most often used species is Acer rubrum (Red Maple). This species though is not used as often as its sap sugar content is much less than that of Acer saccharum and it also breaks bud much sooner than Acer saccharum. This means that the leaves will emerge sooner and therefore most of the sap's water and nutrients are transported to and made into leaves instead of flowing in the tree resulting in less sap production.

Maple trees are tapped for Maple Syrup production early in the spring, with the best Maple Syrup season being from mid-February to early April depending on the weather. This time of the year is the best time for Sugar Maple Syrup production because it is at this time that the tree has sap with the highest sugar content, the most sap flow, and therefore the most sap can be collected. A single Sugar Maple tree can produce around 20 gallons of sap during this season.

Maple trees engage in an interesting mechanism which results in an increased sap flow during this time of year. Early in the spring, temperatures rise above freezing during the day and drop back to below freezing at night. This fluctuation of temperature is the reason why there is so much sap flow during the spring, while the trees are still dormant. During the day time, when the temperatures are warmer, pressure builds up in the tree causing sap to flow out of the tree through the tapped hole. During the night time, when it drops below freezing again, another form of pressure develops in the tree causing water to be taken in from the tree's roots. So then when the temperature gets above freezing again sap will flow once again through the tapped hole. These pressure developments are the result of various factors including osmotic pressure, which results from a higher concentration of sugar being present in the tree than the water from the ground. The sugar that is present in the sap is the result of the sugars produced from the leaves in the previous year. When the sugar is transported to other tissues of the tree, some can get dissolved in the sap.

This cycling between warm and cool temperatures is essential for a good sap season. If the spring gets too warm, where the temperatures never drop below freezing during the night, sap flow is decreased and therefore less Maple Syrup can be produced that year.

During Maple Syrup production the first step requires the tapping of your selection of Maple trees. This is essentially the drilling of a small hole in the tree, which allows Maple sap to flow out of. When drilling of the hole is complete, a tap can be placed in the hole, which will facilitate the drainage of sap into collecting materials. Some individuals use pails or bags to collect the sap, others use tube systems. Tapping of the Maple tree, while can be perceived as harmful to the tree, is not harmful at all. As long as healthy trees, measuring at least 10 to 12 inches in diameter are tapped, no damage will result. Tapping only removes approximately 10% of the tree’s sugar which is an insignificant amount to do any lasting damage. The tree is also successful at replacing the drilled hole with new tissue as long as the tree is healthy.

Ideally collection of sap is done every day because one tree can produce anywhere from a quart to a few gallons of sap in one day. While sap is being collected some individuals will choose to filter the sap before Maple Syrup production. This aids in the removal of debris and insects from the sap. It is also important after collecting to not let the sap sit for too long without making it into Maple Syrup because the sap’s sugar content makes it an ideal environment for bacteria and fungi to grow in. So, it is important to boil down the sap as soon as possible after collecting to prevent this from happening.

Interestingly it requires a lot of Maple sap to make Maple Syrup. It has been estimated that it requires approximately 40 gallons of sap to produce just one gallon of Maple Syrup. This means that a ten gallon milk can filled with sap will produce only one quart of Maple Syrup. Tree sap is approximately 2% sugar and 98% water, whereas the final Maple Syrup product is approximately 67% sugar and 33% water. This means that a lot of water needs to be evaporated or boiled off the sap to get our final product. This method can be done in various ways at varying complexities. The simplest method is done with a large pan and an open fire. Sap is added to the large pan and then boiled down to the desired sugar content.

In order to legally sell Maple Syrup, it must have a sugar content of at least 66%. The optimum sugar content ranges from 66.5% to 67.5%. This is a very small percentage range and therefore sap must be cooked down carefully to prevent the Syrup from being too thick, in which crystals will form when stored, or from being too thin, in which the Syrup can be conceived as sour.

Sap typically reaches 67% sugar content when its temperature reaches 219ºF. A thermometer therefore can be used to determine the relative sugar content of the Maple Syrup. The sap is allowed to boil down to Syrup until it reaches a temperature of 219ºF and then the Syrup is quickly removed before it is allowed to boil down any further.

Another common method of measuring sugar content of Maple Syrup takes advantage of a hydrometer. A hydrometer is an instrument used to measure the relative density of a liquid. The more dense the liquid is, the more sugar it contains. Using a hydrometer is relatively simple and determining the density of the Maple Syrup can be done within seconds. First the Maple Syrup is poured into a container. Then the hydrometer is lowered into the Syrup and it will sink some and then begin to float more or less depending on the density of the liquid.

Along the hydrometer’s stem are various numbers whose meaning depends on the scale. For most hydrometers a common scale is that of degrees Brix (ºBx). This scale tells the percent sugar content of the liquid. Therefore, one ºBx is equal to 1% sugar content. This scale though does depend on the temperature of the liquid at the time of measurement. If the temperature of the Syrup is at room temp or about 68ºF (20ºC) the observed Brix value displays the true sugar content value. However, while the sap is being boiled down, its temperature will be well above 68ºF (20ºC) and therefore will be thinner and measurement will give a falsely low sugar content.

Most hydrometers made for Syrup production are made containing the Brix scale with a Hot test reference line and a Cold test reference line. The Hot test reference line is the line that one will use if the syrup is being tested while above room temperature (typically close to boiling temperature). The Cold test reference line is used when the Syrup being measured has a temperature close to room temperature. So, once the hydrometer is lowered into the liquid, the number read off the instrument, that is at the level of the liquid, represents the specific gravity or density of the liquid. The Brix number for the Hot test is around 59 ºBx and the Cold test value (the true value) is around 66 ºBx. So when boiling down the sap, a Brix measurement of 59 ºBx means the Syrup is at its proper, legal density.

When the Syrup has reached the proper temperature and density it can now must be taken off the heat to prevent further boiling. The Syrup can then be transferred to containers for storage. First, though, the Syrup must be filtered to remove any extra debris called "sugar sand". Now you have your completed product to enjoy over a nice stack of pancakes! To learn more about the chemistry behind Maple Syrup click here.

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Sugar Maple: Acer saccharum

Making Maple Syrup with Acer saccharum

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