When making maple syrup, it is important to monitor the density to determine when the sap has been boiled down enough to make syrup. This is done by using a hydrometer, which measures the specific gravity or density compared to water. The target hydrometer reading for maple syrup varies depending on the grade, but is generally in the range of 66-68° on the Brix scale.
What is a hydrometer and how does it work?
A hydrometer is an instrument used to measure the specific gravity or density of a liquid. It consists of a sealed glass tube with a wider bottom section that contains lead shot or mercury for weight. Inside the tube is a narrow stem with graduations marked on it. When placed in a liquid, the hydrometer will float at a level where the density of the liquid provides enough buoyancy to support its weight. The reading is taken where the liquid surface intersects the scale on the stem.
Hydrometers work based on Archimedes’ principle that states an object fully or partially submerged in a fluid is buoyed up by a force equal to the weight of the fluid displaced. So the more dense a liquid is, the more buoyant force it provides and the higher a hydrometer will float. Less dense liquids provide less buoyancy so the hydrometer will sink lower. By calibuing the graduations on the stem, the specific gravity or density can be read directly.
For maple syrup production, a hydrometer allows the sugarmaker to monitor the density of the sap and syrup during the boiling process. When the target density corresponding to the desired sugar concentration is reached, the syrup is done boiling.
Target hydrometer readings for different maple syrup grades
The standard grades of maple syrup, from lightest to darkest, are:
- Grade A Light Amber
- Grade A Medium Amber
- Grade A Dark Amber
- Grade A Very Dark Amber
- Grade B
The lighter grades are produced earlier in the season when the sap runs clear, while darker syrup comes from sap harvested later in the season. As the season progresses, the sap has higher sugar and mineral contents which affects the flavor and color.
The target hydrometer readings at a standard temperature of 60°F (15.6°C) for each grade are:
| Grade | Hydrometer Reading |
|---|---|
| Light Amber | 66.0-66.9° |
| Medium Amber | 65.5-66.0° |
| Dark Amber | 65.0-65.4° |
| Very Dark Amber | 64.5-64.9° |
| Grade B | 64.0-64.4° |
As you go from lighter to darker grades, the target hydrometer reading decreases, reflecting the higher sugar content. Grade B is the darkest, richest syrup with the lowest target reading.
How to take a hydrometer reading
Taking a hydrometer reading during syrup production is straightforward:
- Collect a small sample of the boiling sap or syrup in a hydrometer cup or cylinder.
- Allow the sample to cool to 60°F (15.6°C). This is the standard calibration temperature for maple syrup hydrometers.
- Place the hydrometer in the cooled sample and allow it to float freely. Spin or swirl gently to release any bubbles trapped under it.
- When the hydrometer stabilizes, note the place where the surface of the liquid intersects the scale. This is the hydrometer reading.
- The hydrometer reading indicates the density, specific gravity, Brix degrees, or percent sugar by weight depending on the scale used.
- Compare the reading to your target value for the grade of syrup you are making.
- If the reading is low, continue boiling to concentrate the syrup further. If the reading is in your target range, the syrup is ready.
It’s important to take the reading at a consistent temperature as the density will change with temperature. Cooling to 60°F gives a standardized reading you can compare to hydrometer scales calibrated at that temperature.
Hydrometer scales used for maple syrup
There are a few different hydrometer scales used in maple syrup making:
- Specific gravity – Measures density compared to pure water which has a value of 1.000. Maple syrup ranges from about 1.320 to 1.370.
- Brix degrees – Measures percent sugar by weight, which maple syrup is approximately 66-68%. Named after 19th century German scientist Adolf Brix.
- Baumé – An older density scale where 0° is pure water and 66° target is standard for maple syrup. Devised by French chemist Antoine Baumé in 1768.
- Percentage by weight – Directly measures the percentage of sugar in the solution by weight. Overlaps with the Brix scale.
Many hydrometers designed for maple syrup use the Brix degrees scale. Brix and specific gravity (SG) can easily be interconverted:
- Brix = (SG – 1) x 142
- SG = 1 + (Brix / 142)
So a Brix reading of 66 is equivalent to 66/142 = 0.465 above water or SG = 1.465. While any of these scales can be used, Brix is convenient as it gives you the sugar percentage directly.
Factors affecting hydrometer readings
Several factors can affect hydrometer readings during syrup production:
- Temperature – Hot syrup will read lower than when cooled. Always standardize to 60°F.
- Purity – Starch, minerals, or other impurities will decrease the reading.
- Sample handling – Bubbles clinging to the hydrometer give false low readings. Gently spin to dislodge.
- Hydrometer calibration – Make sure yours reads 0 Brix in pure water. Check calibration annually.
- Reading errors – Parallax, lens distortion, or bad lighting can make readings inaccurate.
Taking steps to control these factors allows you to hit your target density reliably. Cooling samples, carefully handling the hydrometer, and monitoring calibration minimize reading errors.
Troubleshooting hydrometer issues
If you experience any problems getting accurate hydrometer readings, here are some troubleshooting tips:
- If readings seem way off, double check the temperature. Cool to 60°F (15.6°C).
- Inspect for bubbles adhered underneath, gently spin or swirl to dislodge.
- Look for debris, sugar crystals, or film interfering – clean thoroughly.
- Check for parallax or distorted view, get your eye directly above the reading.
- Verify the hydrometer is floating freely and not touching sides or bottom.
- Confirm hydrometer scale matches the liquid – should read 0 in distilled water.
- Look for cracks, separations or liquid inside that indicate damage. Replace if compromised.
- Consider comparing to syrup refractometer readings for confirmation.
With attention to detail and awareness of potential errors, hydrometer readings can reliably guide syrup making. Follow sound procedures and troubleshoot as needed to hit your targets.
Using hydrometers throughout the syrup season
Hydrometers play an important role throughout the maple syrup production season:
- Early season – Sap is light, readings may start around 1.320 SG when boiling begins. Target Light Amber grade.
- Mid season – Density drops to 1.310 SG as sugar content increases. Make Medium Amber grade.
- Late season – Sap is darker and dense, SG down to 1.300. Produce Dark and Very Dark Amber.
- End of season – Very dense sap creates rich Grade B syrup, SG near 1.270.
Monitoring with a hydrometer identifies the right boiling times and temperatures to achieve your ideal syrup grades throughout the seasonal changes in sap composition. It helps maximize yields from early light sap while also producing darker syrups late in the season.
Hydrometer guidance is key for quality syrup
Using a hydrometer takes the guesswork out of maple syrup making. By measuring the density of boiling sap, it guides the sugarmaker on when to stop the evaporation process for syrup at the desired sweetness, flavor, and grade. Hydrometers are an inexpensive and reliable tool to optimize both quality and productivity in sugarbush operations of any size.
Conclusion
A hydrometer is an essential tool for monitoring maple syrup density and determining when the ideal sugar concentration has been reached based on the target grade. Sap must be boiled until it reaches a hydrometer reading between 66-68° Brix, equivalent to approximately 1.320-1.360 specific gravity at 60°F. Careful hydrometer measurements at a consistent temperature allow maple syrup producers to reliably produce high quality, properly graded maple syrup throughout the sugaring season. Following sound hydrometer usage procedures and troubleshooting techniques will ensure accurate readings.
