Using a hydrometer to measure
the sugar concentration of sap and syrup

Background
Consider a rock and a piece of styrofoam, both the same size. If you put them in a bucket of water, which one sinks? As you know, the styrofoam will float, and the rock will sink. This is because the rock is denser than water, while the styrofoam is less dense than water.

An object's density is a measure of how much it weighs compared to how much space it fills. In the example above, both objects are exactly the same size, but the rock is much heavier. Therefore, the rock is denser than the styrofoam. As with solids like rocks and styrofoam, different solutions (liquids) can have varying densities, too.

Have you had the chance to go swimming in a lake and the ocean? If so, you may have noticed that it was easier to float in the ocean. Because the ocean contains more salt than most freshwater lakes, ocean water is denser than lake water. Objects float higher - or displace less liquid - in solutions with greater density.

A hydrometer uses this principle - density - to measure how much sugar is in sap. If you take a sample of sap from two different trees, the sap containing more sugar will be denser than the sap containing less sugar. A hydrometer measures how dense sap is by recording how much water is displaced when it floats in the sap.

The hydrometer will displace less water (will float higher) in sap that contains more sugar than it will in sap that contains less sugar. Hydrometers use this information to record the sugar concentration of maple sap.

Using a hydrometer
Because producers want to measure the sugar content of sap (1-6% sugar), syrup (66-67%), and concentrated sap (between 6 and 66%), hydrometers are available with several different scales. Some hydrometers can measure the low concentrations of sugar present in fresh sap, while others measure the higher concentrations found in syrup.

Once you have obtained a hydrometer, you may be interested in measuring the sugar content of sap from maple trees in your yard or schoolyard, or you may want to measure the sugar content of maple syrup you have purchased or made yourself. You may even be interested in participating in the Cornell Sugar Maple Tree Improvement Program.

To measure sap sugar content, you will need a hydrometer, and hydrometer cup, and a thermometer. Place the hydrometer cup in a flat pan (the pan will collect any sap that overflows). Completely fill the hydrometer cup with sap or syrup.

Immerse the hydrometer carefully, making sure it doesn't bounce off the bottom, and wait a few seconds until it stops moving. Carefully, making sure your eyes are level with the top of the cup, read the marking on the hydrometer that corresponds with the top of the syrup or sap. Take your readings from the bottom of the meniscus (see Figure 1). The meniscus is the thin film of liquid that adheres to the sides of the hydrometer and is above the true level of the liquid.

Figure 1.

Take the temperature of the sap or syrup inside the hydrometer cup. To be very accurate, you will need to adjust the hydrometer (Brix) reading depending on the temperature. We have provided a table below that contains adjustment information for very concentrated sap and maple syrup (sugar concentration, or Brix, greater than 60.0). If you are interested in accurately determining the sugar content of fresh sap, you will need to do some research to find a similar table.

For maple syrup, use the chart in Table 1 to adjust the reading that you measured with the hydrometer. The "brix" reading from the table is the sugar concentration of the sap or syrup.

Table 1. Brix adjustment scale
Temperature of syrup in hydrometer cup (F)	Correction to be subtracted from (-) or added to (+) observed Brix reading
	60.0 - 69.9 Brix	69.9 Brix and higher
45	-1.0	-1.0
50	-0.8	-0.8
55	-0.5	-0.6
60	-0.1	-0.1
65	-0.1	-0.1
68	0	0
70	+0.1	+0.1
75	+0.3	+0.3
80	+0.5	+0.5
85	+0.8	+0.8
90	+1.0	+1.0
95	+1.2	+1.2

Obtaining a hydrometer
Hydrometers can be obtained from most maple syrup supply companies, and have prices starting at $10. You will also need a hydrometer cup, which costs about $15. Some companies to consider include Waterloo/Small or Dominion & Grimm.