Measuring the density of finished maple syrup accurately is an important task for commercial syrup producers. Many producers aim to produce quality syrup that meets the minimum legal density in Ontario of 66 °Brix. While various reliable methods are available to measure syrup density, some producers, or specific groups of producers have difficulty each year in achieving the minimum density of syrup.
Although the minimum density will satisfy regulators, pleasing the palates of your customers may be a better target to aim for. Like the Vintners Quality Alliance (VQA) of prized Ontario wines, a focus on achieving the best possible quality of maple syrup and maple products will improve the chances of customers returning to the farm year after year. Proper hot-packing of syrup is necessary to ensure both food safety and quality.
Seasoned maple syrup producers and expert judges of maple syrup competitions will often say that the best flavour and texture of high quality maple syrup can be achieved at a finished density of 67 °Brix, or near to it. Although taste is subjective, the syrup is noticeably thicker with a better ‘mouth-feel’ when the density is increased by merely one degree of Brix above the legal minimum density. Dr. Michael Farrell of Cornell University’s maple research station writes ‘all we have to do is boil the sap a bit longer to get the syrup a tad thicker’. For this reason the minimum legal density of syrup in Vermont is 66.9 °Brix. Densities higher than 68 °Brix can lead to crystallization in syrup due to over-saturation of dissolved sugar particularly in cooled syrup, from room temperature down to refrigeration temperature.
To achieve the desired density, modern syrup producers use sophisticated electronic equipment that removes finished syrup automatically from the syrup pan by constantly measuring the elevation of boiling point temperature of 104.2 °C (219.5 °F) at the syrup draw off valve, and monitoring the desired density (67 °Brix for boiling point indicated).
Many syrup producers also have good results using less sophisticated conventional equipment to measure the density of syrup including: a hand-held refractometer, hydrometer, hydrotherm, and various portable electronic density meters. A reliable thermometer, or two, is also needed.
The precision of measurement equipment depends on it being accurately calibrated during each boil. Accuracy also depends on the ability of each producer to understand how to use the equipment as it was designed. Instructions on calibration and proper use should accompany measurement equipment at the time of purchase. Syrup production manuals also describe proper use of density measurement equipment.
New hydrometers are calibrated at the factory at a specific temperature, for example at 15.5 °C (60 °F). Along with the hydrometer, a reliable thermometer that is calibrated to ambient barometric pressure is essential to make corrections to density readings from the hydrometer. Correction is necessary where the temperature of the syrup sample is above or below the calibration temperature of the hydrometer (Photo 1). With each hydrometer reading, correction charts are consulted to either add or subtract a °Brix value from the observed density. The correction value is based on the temperature of the syrup being tested. Some electronic density readers can automatically correct for the temperature of a syrup sample.
Photo 1. This hydrometer reading indicates the syrup has a density of approximately 66.5 °Brix and does not need correction if the temperature of the syrup is 15.5 °C (the calibration temperature of the hydrometer). Using the correction table, if the syrup temperature is 30 °C the density would be corrected to 67.7 °Brix. If the syrup temperature is 2 °C the actual density would be 65.3 °Brix, or under the legal minimum density in Ontario.
Relying on only one method of measuring density is risky. Producers will have more confidence in finished density where comparisons can be made during syrup processing and prior to bottling. For example, an identical density reading from two separate hydrometers, or comparing with another syrup producers’ measurement equipment will provide confidence in density measurements.
Comparing density readings can detect inaccurate equipment. For example, the paper density scale positioned inside the stem of a hydrometer can slip unnoticed, which will make readings erroneous.
Where syrup producers strive to please their customers first with palate-pleasing syrup, it will reduce concerns of falling below the minimum legal density. Having confidence in measurement equipment is the key to success.
Photo 2. A portable electronic Misco density reader can quickly measure syrup density. Like all measurement equipment, it must be properly calibrated prior to use.