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Will Tap Holes Close Up if You Tap Maples Too Early?

Feb 4, 2025 | DIY Maple Syrup

Knowing when to tap is one of the biggest challenges for a maple syrup producer. There is no clear answer to the question of when to tap. The right time to tap depends on “a combination of inexact science, the vagaries of weather, microclimate, intuition, and luck.” (North American Maple Syrup Producers Manual, 3rd Edition) Tapping the tree too late means you can miss much of the early sap production. Tapping too early increases the risk of a decrease in sap production later on. Is that because tap holes will “close up” if you tap maples too early? Yes! Here’s why.

Why would anyone want to tap early?

Tapping early (but not too early) is important, because there is more sap flow at the beginning of the season than at the end. The sap that flows at the beginning of the season also tends to have a higher sugar concentration, which, in part, causes the sap to be of higher quality. Throughout the season, the sugar concentration in the sap typically drops.  Towards the end of the season, the sap and the syrup that is made from it can have a sour or bitter taste. Typically, you should tap when the nighttime temperatures are consistently freezing and daytime temperatures are consistently above freezing. How do you know when the season is over? When the trees start to bud, it’s time to stop sugaring.

Tapping early may seem like a good idea, and it makes sense that maple syrup producers want to capture all of that early-season sap. In reality, however, it can slow or even stop the sap flow from the tree later in the season. This can be due to microbial growth and taphole “drying”.

What is taphole “drying?”

Taphole drying is a term that refers to when a tap hole does not yield any sap (and is therefore “dry”) even if the weather conditions for sap flow are met. The name is slightly misleading, as the taphole does not actually dry up. In reality, it is the result of a natural wound response procedure by the tree resulting from the exposure to air and microorganisms that occur when tapping. This exposure causes the tree to “wall off” the injured area. This is the tree’s way of preventing the spread of infection.

Unlike with animals, the wound in a tree is never filled with new tissue. Instead, the trees form new structures to seal off the severed vessels. The hole never goes away, it just gets covered by new wood during the growing season. The tree also utilizes different antimicrobial cowmpounds which makes the injured area less hospitable for the bacteria and fungi. However, when this happens, the area around the injury is unable to transport sap. So, as this “wall” forms, the sap flow is continually restricted.

What causes “walling-off?”

The walling-off response begins right after the tap hole is drilled. However, the amount of time that a tap hole will remain operational depends a lot on the method of collection and the sanitation of the tapping system. When tapping “traditionally,” using buckets, tapping should be done shortly before the sap flow begins. This is because the inside of the tree is directly exposed to air, and therefore will “dry” a lot faster than when using a tubing system, where the tap holes are closed off to the air.

However, even when using a tubing system, spout and dropline sanitation, as well as weather conditions still play a big role in producing a good sap flow throughout the season. Generally, the length of the season when using buckets is around 4-6 weeks, while tubing systems with vacuum can result in a longer season, around 3-4 months. Unfortunately, sometimes the weather, especially temperature, can affect the season’s length.  In warmer temperatures, there is an increase in microbial growth which can plug the tap holes and restrict sap flow faster.

What are good sanitation practices?

When tapping with buckets, keeping the tap holes clean is quite difficult. The tap hole is open to the air, meaning that any organisms in the natural environment can easily make their way into the hole. However, you can sanitize your tap spouts every year before tapping. First dip-rinse them in a chlorine bleach solution (one part of unscented chlorine bleach to 20 parts of water). Then rinsing them in hot water. Alternatively, just boil the spouts in clean water.

When using tubing, there are several practices that can maintain cleanliness in your tap holes. Again, boiling the taps before every season to sterilize them can help. Or you can buy new disposable spouts every year that can easily attach to the sap lines, rather than reusing the spouts that have been hanging out in the woods (or elsewhere) since the end of the last season.

One concern is that when using the same tubing year after year, it will eventually start to fill up with bacteria. If you use a vacuum pump, the trees pull the excess sap (full of bacteria from the tubes) back into the tap holes every time you shut off the vacuum pump. This is less of a big deal when using a natural vacuum, as many hobbyist sugarmakers do, because there is no “pump” to turn off. (Users of our Beginners Tubing Kit for 25 Taps use natural vaccuum, for example.)

Still, if you want to go even further, sanitizing the tap lines is also an option. Some sugarmakers use a chlorine bleach solution, forcing it into the tubes and leaving it for a few days and then flushing them with water and/or letting the first sap run of the season run onto the ground to wash the residue of the bleach out.

What about isopropyl alcohol?

When we used a bleach solution in our lines, we  found that squirrels were attracted to the salty residue of the solution after evaporation, and proceeded to damage the sap lines extensively. In order to circumvent this problem, we simply left our tap lines open to dry over the last season. Less sanitary, but also less squirrels. In Canada, sugar makers flush lines with isopropyl alcohol, which sanitizes without attracting critters. Frustratingly, this method has been foreclosed to US producers by the EPA. (Insert grumpy emoji face here.)

What’s the bottom line?

The bottom line? If you are collecting sap using buckets, it’s best not to tap until temperatures are consistently right for sap collection, lest your tap holes “dry up” before the season starts in earnest. If you are using a tubing system, you can tap a bit earlier, but remember to employ the best sanitation practices available to you! This is especially important if you run a vacuum system. And eventually (as in at least about every 10 years) even sanitized sap lines should be replaced with new ones to protect your trees and your syrup quality.

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