Re: What type of tool would be used to measure the sugar-level in sap?

There are a number of ways that this can be done, however the normal 
methods call for either expensive equipment or large volumes of sap.  

Before I get into the specifics about some possible approaches there are 
other factors which you will need to take into account.  Sugar maples have 
the highest sugar contact, about 2-2.5% in northern states where it is 
normally harvested.  The sugar content may be different in Florida due to 
dramatic climatic differences.  If you don't have access to sugar maples 
then the process could become more difficult since other trees have even 
lower sugar content.  When making maple syrup there is less concern about 
the starting sugar content than with the final content, making its 
measurement less important.

I'll cover some methods and make some suggestions, however you will 
probably need to conduct some experiments to see which works best (or 
which works at all).
1.  In industry we would normally use a refractomer.  This instrument 
measures the degree to which light is bent when passing through a liquid.  
Sugar causes the light to be bent to a greater degree than pure water, the 
more sugar the more bending.  Refractometers come in different ranges of 
brix (the refractive index is correlated to percent sugar which we term 
brix or degrees brix).  Even the cheapest hand held refractometer is 
fairly expensive, running in the area of $350.  Most refractometers are 
designed to read at much higher sugar levels, so a specialized instrument 
might be even more expensive.
2.  Maple syrup is actually a mixture of sugars, primarily glucose and 
levulose.  Diabetic dip sticks used for urine or glucometers used with 
blood actually measure glucose so they could theoretically be used.  The 
problem comes with the amount of sugar in the sap.  As an example (I am 
diabetic) I try to maintain by glucose level at 150 or less on my 
glucometer, this means 150 mg of glucose per decileter (100 ml) of blood.  
If we assume that 1 ml of blood is equal to 1 gram (its actually a little 
heavier) then we would have 150 mg/100 g = 0.15 g / 100 g = 0.15 % 
glucose.  This is greatly below the amount in sugar maple sap which means 
the instrument wouldn't be able to measure it because the amount is to 
high.  You could try diluting the sap with water to get the concentration 
down to a readable level then convert it to amount in the original sap.  
Depending on your sap a dilution of 1 part sap to 5-10 parts of water 
would probably work.
3.  Hygrometers measure the density of a solution (sap is a sugar in water 
solution) and are calibrated to provide output as a %.  Hygrometers are 
long tubes that are weighted at the bottom.  They are immersed in the 
liquid and when they come to rest the level red off the stem, much like a 
mercury thermometer.  They require a large volume of liquid and, again, 
are not normally produced to read such small quantities of sugar.
4.  Another way to measure density is to weight a given amount of liquid.  
If you have access to an analytical balance (one that can weight 0.001 to 
0.0001 grams you might be able to pick up weight differences resulting 
from a change in sap composition.  You would have to very accurately weigh 
a very precise volume of sap.  Pipettes can allow you to do this, however 
the more precise the pipette the lower the volume you can deliver and the 
more difficult it is to identify a difference in weight.
5.  There are also chemical methods to quantify sugar content.  These 
require specialized equipment, chemicals and procedures that are probably 
not suitable for your purposes.

I recommend trying #2 with #4 as a back up if you have access to an 
analytical balance.  

For number two you would need to get some sap.  Accurately, weight or 
volume, mix one part of sap with 5 parts of water (i.e. 1 g or ml of sap 
with 5 g or mls of water).  Take a reading with the glucometer.  Adjust by 
adding less water if the reading is to low or more water if it is to 
high.  Try to get near the mid-range of your glucometer, with mine that 
would be a reading of 150-200.  You will need to make sure that your 
technique is measuring is very good, a small difference in amount will 
result in a large difference in the reading.

If #4 is better for you try the following:
-  Go the store or druggist and get glucose 
-  Accurately weigh different quantities of glucose into a water, probably 
in small increments like .5 g to 2 g in 0.1-0.2 g increments.  
-  Accurately pipette into a tared (pre weighed) container using very good 
lab technique.  Remember, very sensitive analytical balances will be able 
to pick up the weight of oils and moisture from your hand if you pick up 
the container.
-  Again you will probably need to try increments to see which works best, 
maybe 1 ml, 2 ml, 5 ml, 10ml, 25 ml (depending on pipettes available since 
it will be best to use a pipette that measures the quantity in one drawing 
of the liquid).
-  A graph of weight on the y-axis and amount of glucose on the x-axis for 
each volume will help you identify which pipette size gives the best 
result.  The best line will be one which is flat, not having a lot of ups 
and downs.

Good luck.