Filtering maple syrup after boiling is important. The filtering stage of making maple syrup will remove any ash or other debris that may have ended up in your syrup while boiling, and it will also remove any nitre or sugar sand that is bound to be present in your home made maple syrup.
Check out this video of finishing and filtering maple syrup:
The last steps in finishing your maple syrup are tricky. You have to bring your syrup up to precisely 104C/219F using a calibrated thermometer for your syrup to be considered pure Canadian Maple Syrup. Doing this requires a very accurate candy thermometer, or a maple syrup hydrometer or refractometer of some sort. To clarify your syrup, you’ll want to filter it out in one way or another.
As your sap boils away and steams off it’s water, the colour changes from clear to yellow, then finally to the golden colour that we are all used to seeing in the finished product on store shelves.
Finished syrup also holds a large amount of nitre, or sugar sand. Nitre is a buildup of nutrients in the sap. The tree pushes sap up out of its roots and into its branches to begin feeding the tree in the spring before leaves have formed and photosynthesis can begin. As you boil down your sap, these nutrients form the nitre, or sugar sand that will eventually end up settling in the bottom of whatever vessel you might store your finished maple syrup in.
We finish our syrup on either a two burner outdoor propane stove, or a turkey fryer. In both cases, it is in a large stainless steel pot. Near syrup, or nearup as we call it, comes out of the evaporator, filtered to remove any ash or other debris that may have ended up in it, then straight into the large stainless pot to be finished. The nearup is boiled to 104C/219F at this point. Or 66 to 68 brix.
Once the syrup is finished, it is once again filtered through either paper filters, such as cooking oil cone filters, or a large orlon filter designed specifically for maple syrup finishing.
It’s helpful to keep your syrup hot while filtering it out. Hot syrup will pass through the filters, especially paper filters, much easier than cold syrup will. Depending on the season and your syrup, nitre buildup may be very heavy, causing clogged filters. If this is the case, you’ll need to rinse the filters in hot water periodically to keep the syrup flowing through.
At this point, your syrup is done and ready to be bottled for long term storage!