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.