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Stephen Childs
07-14-2008, 11:22 AM
Using a Diabetic Glucose Meter to Test Invert Sugar in Maple Syrup

Sucrose is common table sugar and is the only sugar in sap when it comes from the tree. Some of the sucrose in sap is converted to invert sugar as a result of microbial fermentation during handling and processing. Microbial metabolism is temperature dependent and occurs to a greater extent in sap that is collected late in the season when temperatures are warmer. A certain amount of invert sugar is desirable in maple syrup that is to be made into a maple confection with each confection having its own ideal, acceptable, and unsuitable levels.

In general, all grades of maple syrup contain some invert sugar. The amount varies among different grades. Lighter syrup particularly that made early in the production season, generally has the least invert sugar. Very dark syrup, particularly that made during warm spells late in the production season, will have the most invert sugar. Testing has shown a wide variation in invert levels in the different grade classifications. This variability of invert sugars in syrup makes it helpful to test and adjust the invert sugar levels to match the specific characteristics desired for a given confection. Testing syrup and adjusting to a proper invert sugar level can eliminate batch failures and help the maple producer make confections of consistent quality. For many years the use of the Clinitest tablets was suggested as the way to measure invert sugars in syrup. Now, a simple test using the common glucose meter used to monitor blood sugar can be very helpful in selecting and blending syrups to make the most consistent products. Testing syrups before they are purchased for the purpose of making confections assures you are getting syrup that will make the confections you want.

Diluting Syrup to Measure Glucose
Maple syrup cannot be tested directly with a glucose meter. It is too thick and will not properly enter the test strips. To solve this problem dilute the maple syrup with water before testing. The most accurate and easy method is to dilute by weight. This is best done with a scale. Scales with one tenth of a gram (0.1 g) accuracy and a range of 0 to 300 or 600 grams are now available at reasonable costs and are easily ordered on the internet. A one in ten dilution of syrup seems to work well for most syrups, it is easy to calculate on a scale, and gives a reading on the glucose meter that is in the range for invert sugar concentrations required for most confections. Once you have a scale and are familiar with it's operating instructions, follow these simple directions:
Place an empty cup on the scale
Tare the scale to read 0 with the cup in place
Drip 10 grams of syrup into the cup
Pour 90 grams of warm water into the cup, adding the last amounts slowly in drops
The scale total should now read 100 grams total
Remove the cup from the scale and stir the water and syrup vigorously

Your maple syrup 1 in 10 dilution is now ready to be tested with a glucose meter.

Types of Glucose Meters
There are a wide variety of glucose meters available in drug stores, the pharmacy section of department stores, or on the internet. Most glucose meters should be useful for measuring glucose in maple syrup, but meters that give numerical readings throughout their range (rather than Hi/Lo at the extremes) are best. These can range in price from nearly $100 to less than $10. There is also a wide range of prices for the test strips used in the various meters. Consider both the initial cost of the meter and the cost of test strips in determining which to buy. The more expensive meters offer recording and storage of information options that will be of no use to maple producers. These meters should be used at normal room temperatures and humidity. Each batch of test strips needs to be calibrated to the meter. This is done automatically in most cases, but follow the directions with your meter. Store your meter and test strips in a place protected from dust, fluids, and extremes of temperature and humidity.

Meter Use
Most meters operate with a similar procedure in that you remove a test strip from it's protective foil and insert it correctly into the meter. Insertion of the test strip will turn the meter on automatically, give a notice of calibration, and then ask for a sample. With most meters follow these simple directions:

Open a test strip being careful to only touch it in the middle.
Slide the test strip into the meter. Follow the directions that come with the glucose meter to insure you put the correct end of the test strip into the meter and that the correct side of the strip is up, otherwise the meter will not give a reading.
When the meter indicates it is ready for a sample, dip the extended end of the test strip about inch into the syrup dilution and hold until the meter indicates the sample has been activated.
Move the meter to a horizontal position with the test strip in place and wait for the reading to appear on the screen

The reading that appears on the screen will either be a number, or it may say Hi or Lo. Here you will need to read the manual that came with the meter to know at what number the meter begins reading Hi or Low to understand what range they represent. The reading on the screen should be given as mg/dL or milligrams per deciliter. Most meters read glucose concentration in whole blood. Some meters convert these reading to glucose in blood plasma, which is 10-15% higher. Our recommendations are based on the whole blood readings.

Accuracy and Repeatability
Repeatability means the meter will give the same reading when you sample the same solution again. Accuracy means how closely the meter reading is to the actual glucose amount.

The Food and Drug Administration regulates the quality and manufacture of blood glucose meters and test strips. However, the accuracy of affordable meters is 10-20%. This means that if you test your meter, repeated readings can be very different and still be within the accuracy tolerances of the meters. For instance if the invert sugar level in the sample were exactly 1% and your meter read 50mg/dl it would be perfectly correct but you should expect readings to vary between 45 and 55mg/dl if you took a number of reading from this same sample. At these low sugar levels this amount of variation is completely acceptable and gives you a close enough knowledge of where the invert sugar levels are in your syrup to make good blends and confections. You should understand though that as the invert sugar levels increase the 20% variation also becomes a bigger number. A 10% invert sugar solution (500 mg/dL) could give a reading between 450 and 550mg/dl.

You should check your meter periodically with repeat measurements on the same sample (with different test strips) to get an idea as to what to expect. Be sure that the sample is well mixed. Despite their limitations, these meters are a big improvement over the Clinitest tablets.

Testing Barrels
Once the syrup is in a barrel the invert sugar level will generally be stable unless a bacteria or yeast fermentation becomes active or the syrup is heated again. An invert sugar test can be run on barrels or other storage units as they are stored or a small sample can be held out from each barrel and all samples tested soon after the season so that the syrups can later be selected for use making confections or blending. Retesting when a barrel is opened is recommended, or testing can be performed as a batch of syrup being used.


In summary, when making maple confections we recommend that you:
Measure and record the invert sugar levels of your stored syrups
Pick the best syrup for a confection based on the invert sugar levels
Or, blend syrups to get the invert sugar level you want

Glucose meter reading/ % Invert sugar in the syrup
mg/dL/ invert %
20 / 0.4
30 / 0.6
40 / 0.8
50 /1
60 /1.2
70 /1.4
80 /1.6
90 /1.8
100 /2
110 /2.2
120 /2.4
130 /2.6
140 /2.8
150 /3
160 /3.2
170 /3.4
180 /3.6
190 /3.8
200 /4
210 /4.2
220 /4.4
230 /4.6
240 /4.8
250 /5

The New York State Maple Confection Notebook describes the ideal and useable invert sugar levels for each common maple confection. Other sources also suggest acceptable limits for invert sugar in various maple confections. The math for blending syrups is simple but a subject for another day.
Steve Childs, NYS Maple Specialist