Density Testing & Adjustment

Hydrometers are well adapted for use in the sugarhouse as they can be used to measure the density of syrup from well below room temperature to near boiling. The depth at which a hydrometer floats in syrup depends on the syrup's "thickness" which is a function of both syrup density and temperature. When a hydrometer is placed in syrup at the calibrated temperature, the hydrometer reads the correct density. At all other temperatures the hydrometer reading must be corrected. Most hydrometers commonly used in the maple industry are calibrated at 60°F (15.6°C). The table below presents the corrections needed for each temperature. For example, if the syrup density shows as 65.8°Brix on the hydrometer and it's temperature is 80°F (26.7°C) an additional 1.0°Brix must be added to calculate the actual syrup density. All maple syrup sold in the Province of Ontario must be a minimum of 66°Brix.

No matter how skilled an individual producer may be at finishing syrup, most will occasionally produce syrup with an unacceptable density. Maple syrup with too low a density is not legal to sell, will spoil more quickly, and is thin and runny. Syrup that is too thick will produce sugar crystals which is unappealing to consumers and costs the producer lost revenue by using more syrup than necessary. If the syrup's density is too low it must be reprocessed to a higher density which can result in additional grade loss and added expense in filtering. If the density is too high it only needs to be mixed with the right amount of pure water to acheive the desired Brix. Because of the difficulty of drawing off a full batch directly from the evaporator at the perfect density many producers will instead draw off a little over density then thin it during finishing. The table below shows the amounts of pure water to add to finished maple syrup to reduce 4L of syrup in 1/4 °Brix increments.

How to Avoid Double Shadow-Lines when Making Density Measurements.

The refractometer is commonly used to spot check the syrup when it comes from the finishing pan. Hot syrup applied directly to a cold instrument will not give a distinct shadow-line and may damage the prism. When a drop of hot or warm syrup is applied to a refractometer prism that has a temperature of 10°C or more cooler than the sample of syrup, the drop of applied syrup will cool rapidly. As the drop of syrup cools to the temperature of the prism, a layering of different densities occurs of the liquid, producing multiple shadow-lines, which cannot be read accurately. It is, therefore, important to take the following steps when checking hot syrup. First, cool the sample of syrup to a temperature of 65°C (150°F) before it is applied to the refractometer prism. To do this quickly, place the hot syrup in a 10 mL (half ounce) salad dressing cup in the snow. Stir the syrup sample in the cup for about 5 seconds. Secondly, using a plastic stir stick smear the drop of syrup on the prism for about 15 seconds before closing the cover. This stirring will create a homogeneous layer of syrup, which will provide a single and clear shadow-line. After a drop of syrup has been tested, the refractometer should be cleaned by wiping the syrup off the glass prism with soft tissue paper and cleaned with rubbing alcohol. Calibration oil is available from some maple syrup equipment dealers. Check the label for its correct calibration density.