A spile, sometimes called a tap or spout, is a simple, hollow device inserted into a tree trunk to facilitate the controlled collection of sap. This tool acts as an interface between the tree’s pressurized interior and the exterior collection system, such as a bucket or tubing network. The spile captures the sugary water flowing from a drilled hole and directs it efficiently into a container. While various trees can be tapped, the spile is most famously associated with collecting maple sap for syrup.
Spile Design and Basic Mechanism
The physical design of a spile is engineered to achieve a secure seal and manage the outward flow of liquid. Most spiles feature a tapered end driven snugly into the precisely drilled hole in the tree’s sapwood. This tapering matches a common drill bit diameter, such as 5/16-inch, creating a tight fit that prevents sap from leaking between the tool and the wood.
Spiles are commonly made from galvanized metal, aluminum, or food-grade plastic, depending on the collection method. Traditional metal spouts include a hook to hang a bucket directly beneath the tap hole. Modern plastic spiles connect to extensive networks of tubing, allowing sap to flow by gravity or vacuum pressure to a central collection tank. Regardless of the material, the device’s hollow core channels the liquid outward and into the receiving vessel.
The Biological Basis of Sap Flow
The mechanism causing maple sap to flow out of a spile is a physiological process unique to maples, driven by specific temperature fluctuations. This relies on a cycle where temperatures drop below freezing at night and rise above freezing during the day, typically occurring in late winter or early spring. During the cold night, negative pressure develops within the tree’s xylem vessels, causing the tree to draw water up from the roots and soil.
As the wood temperature drops, gases inside the xylem cells contract and dissolve into the sap. Water begins to freeze along the cell walls, creating a suction that pulls more liquid into the wood. When the temperature rises above 32°F (0°C) during the day, the ice melts, and the dissolved gases expand rapidly. This expansion generates a powerful positive pressure inside the tree trunk.
When a hole is drilled and a spile inserted, it interrupts this high-pressure system within the tree’s water-conducting tissue. Because the internal pressure is greater than the external atmospheric pressure, the sugary xylem sap is forced out through the spile. This flow is distinct from the root pressure mechanism seen in other trees, as the pressure is generated primarily in the stem and branches in response to the freeze-thaw cycle. The flow ceases when temperatures remain consistently above or below freezing, or when the trees begin to bud.
Proper Tapping Techniques
Successful sap collection requires careful application of the spile, beginning with the correct preparation of the tree trunk. The tap hole should be drilled into healthy, light-colored sapwood, avoiding visible areas of dark or discolored wood from previous years’ tapping. Use a sharp, clean drill bit, typically 5/16-inch in diameter, to create a smooth, round hole that matches the spile’s size.
The hole should be drilled to a depth of 1.5 to 2 inches to reach the most active sap-conducting wood near the surface. For optimal drainage, the hole should be drilled at a slight upward angle, encouraging the sap to flow out by gravity without pooling inside the tree. Once the hole is clear of wood shavings, the spile is gently tapped into place with a small hammer or mallet until it is seated firmly.
The spile must be tight enough to create a seal and support the collection container, but it should not be driven so aggressively that it splits the wood. When placing new taps, avoid placing them too close to old tap holes; a minimum distance of six inches horizontally and two feet vertically from a previous hole is advised. This careful placement ensures the tap is in fresh, productive sapwood, maximizing sap collection.