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MAPLE SUGARING FACTS
I thought that it would be a good idea to share all of the technical information that I have learned
about the sugaring process. Much of the following information comes from the Ohio Extension
office web site. They actually go into far more detail than I have. I have also added bits and
pieces of information that I gleaned off of other web sites as well as Karla Emery's Encyclopedia
of Country Living and Backyard Sugarin' by Rink Mann. And of course, some of my own
observations and theories are included as well.
WHY DOES MAPLE SAP FLOW?
The very first question that I had about maple sugaring was, very simply, why does maple sap
“flow”? What exactly is this flow process that allows us to collect the sap in late winter and boil it
down into maple syrup? As I did my usual internet research I learned that the physiology of
maple sap flow is not even completely understood by maple sugar experts. Everyone seems to
agree, however, that the flow is triggered by wounding the tree during the late winter and then
"harvesting" the sap that flows from the wound. A flow can be triggered any time during a maple
tree’s dormant winter season when the temperatures fluctuate above and below freezing. Over
the years, however, sugarers have learned that flows are usually the largest during the late
winter and early spring months of February, March and April. These are the months when above
freezing daytime temperatures are often followed by below freezing nights.
It is these fluctuations in air temperature that cause the sap to flow. The freeze/thaw cycle
actually results in an increased pressure inside the tree’s sap wood, and it is this increased
pressure that forcefully pushes the sap out of any wounds in the wood, resulting in the sap
“flow”. I found it interesting to learn that the pressure inside the tree, can be well above the
atmospheric pressure outside the tree.
But I wondered, why does the pressure inside the tree rise? As I understand the process, when
temperatures fall below freezing, the sap in the tree's sapwood freezes. The sapwood is the
youngest wood closest to the bark through which the sap moves. Gasses in the sapwood are
contracted with the below freezing temperatures, and this contraction creates a negative
pressure in the wood that results in a suction. This suction, down in the roots, then draws water
from the surrounding soil into the tree. It is this added water that increases the sap’s volume
and increases the pressure inside the tree. When the temperature then rises above freezing,
the frozen sap thaws, increasing the sap volume even more and creating an even greater
positive pressure inside the tree. The increase in pressure seems to start in the smaller
branches and twigs, then moves into the trunk, and finally, down to the tree’s roots. I found it
quite amazing to learn that an untapped maple tree’s positive pressure can rise to 40 or more
pounds per square inch during the thaw phase of the cycle. When temperatures fall, the
process is reversed, the pressure is reduced, and the flow stops. It stands to reason that
weaker sap pressures result if the temperature does not go below freezing long enough for ice
to form inside the sap wood, causing the initial contraction and suction process to begin. Thus,
good sap flow weather is below freezing nights followed by sunny above freezing, warm days.
A single period of sap flow can last anywhere from one to two hours to or even up to twenty
hours in length. It is thus not unusual, during a typical sap flow season, for the flow to stop
temporarily, when suitable freeze/thaw temperature cycles do not occur. The flow obviously
stops for the year, when the temperature cycles no longer drop below freezing.
WHY IS MAPLE SAP SWEET
I learned that the sugar in maple sap is produced by photosynthesis that took place during the
preceding year's growing season. Photosynthesis, or the tree's ability to absorb sunlight and
turn it into usable tree energy, produces carbohydrates, that the tree stores as starch, although
some carbohydrates may be stored as sucrose. During the winter, maple trees, convert some
of this starch into sucrose which is dissolved in the sap. The amount of sugar in the sap
depends on many factors, such as the genetics of the individual tree, the quality of the site on
which the tree is growing, the tree's health, local environmental conditions, the weather
conditions of the previous growing season, and the weather conditions of the current tapping
season. Generally, sap sugar content is lower at the beginning of the sugar season, rises
rapidly towards the middle of the season, and then slowly declines until the sap stops running.
MAPLE SUGARING EQUIPMENT
There is not much equipment required for sugaring. You probably have almost everything you
need in your kitchen and basement right now. For collecting the sap, you need a drill, a 7/16
drill bit, a tap (more technically called a spile), a small mallet, and a clean jug or bucket with
which to collect the sap. For the boil down process all you need is a source of heat, a large pan,
a filter, and glass jars.
HOW TO SET A TAP
Historically, maple sugarers believed that healthy, vigorous maple trees could support as many
as four or more taps. This view has recently changed as sugarers have realized that many
modern maple trees are not in the best of health. Modern trees commonly suffer from a variety
of stressing factors, including wounds inflicted by fence row clearing, insects, diseases, drought,
soil compaction, and air pollution. In recent years, maple trees throughout much of the
northeastern United States have been subjected to severe stress from an infestation of gypsy
moths. Pollution has also taken a recent toll on maple tree health. The effect of these stressing
factors can easily be measured by the thickness of the trees' recent growth rings. Tapping
guidelines have accordingly become more conservative. It is now recommended that you never
tap a maple tree that is less than twelve inches in diameter, and no more than 2 taps should
ever be set in any one tree, no matter how large the tree. Maple sugarers have recently
realized that the volume of sap produced at each tap hole increases substantially when fewer
tap holes per tree are used. In short, using more taps per tree does not mean that one can
collect more sap from that tree, and with fewer taps per tree, each tap produces more sap.
The first step in setting a tap is to drill the tap hole. Use a clean, sharp 7/16 inch diameter drill
bit. We drilled our tap holes about two feet above the ground, over a large root and under a
large overhead branch. We had learned that the sap seems to flow best between such a root
and branch. We angled each tap hole up into the tree, so that gravity would assist the sap in
flowing out of the hole. Another reason for slanting the hole up into the tree, is to prevent any
sap from pooling inside the hole and freezing. Such sap would be more likely to freeze and
expand and widen the tap hole allowing sap to flow around the tap's seal and leak down the side
of the tree, uncollected. It is important to use a sharp bit, for a dull bit would tend to create a
ragged tap hole which would not only impede sap flow, but would provide additional surface
within the hole that would encourage the growth of micro organisms. Dull bits are also more
likely to produce oval holes which will again allow the sap to leak around the sides of the tap. It
also seems that sharp bits not only cut clean round holes, but that these clean round holes are
easier for the tree to later close or cure, when the tap is removed after sugaring is done for the
season.
If the tree has been tapped before, any new tap holes should be at least 6 inches to the side of
the old ones. Tap holes drilled in successive years should not be placed in a straight line around
the tree. I learned that a useful pattern is to drill each new tap hole at least 6 inches to the side
and slightly above or below the old tap holes. This results in a spiral pattern of tapping around
the tree, and over progressive years, utilizes the entire tapping surface of the trunk. Similarly,
tap holes should be at least 6 inches from old branch scars or other wounds, even if they have
healed over. Tap holes should also only be made into sound, healthy, light colored sapwood.
Decayed or discolored wood should not be tapped. Tap holes should also extend no deeper
than two inches into the sap wood and should never go as far as to reach the tree's darker
heartwood.
I learned that drill bits should also be as clean as possible in order to minimize any
contamination of the tap hole. The bits can be washed with dish soap, well rinsed, and then
soaked for at least 15 minutes in a bleach solution (1 cup of commercial household bleach per
gallon of water) or in alcohol. This soaking kills any bacteria. If you find that you have
encountered rotten wood while drilling a tap hole, the bit should be rewashed with bleach to
prevent transferring any contamination from that rotten hole to another tree. And at all times
during the tapping process, you should try to avoid allowing the drill bit to contact the ground or
any other unclean surface, again so as not to spread any contamination from fungus or animal
feces that lie on the ground.
We drilled our tap holes with an old carpenter's brace that Greg had inherited from his father.
Our first season we only drilled three holes, our second season eight and our third season
thirteen, but I could imagine that if we had been setting one hundred taps, the brace would have
been slow going, but for our few tapped trees, it worked just fine. It somehow felt good to use an
old hand powered tool. A variety of tapping tools are used by more commercial sugarers,
obviously including battery powered drills, but also including gasoline powered adaptations to
chainsaw engines! The main differences between the types of tapping tools used are the cost
and speed of tapping. Powered tappers are obviously more economical for larger maple syrup
producers.
The taps, also called spouts or spiles, have three important functions. They first work to transfer
the sap from the tap hole into a container or tubing. Their next function is to provide support for
either a hanging collection container or tubing that leads to a collection container. Finally, the
tap spouts provide a seal around the tap hole that prevents leaking and minimizes contamination
by micro organisms. Spouts have evolved from the early days when hollowed out reeds or
wooden dowels were used, to the metal or even plastic spouts used today. All modern spouts
are tapered to form a tight seal against the bark or outer sapwood when they are seated firmly in
the tap hole. Spouts, as noted above, must be clean and rust free. At the end of each season,
they should be cleaned with detergent or bleach, rinsed, and then dried and stored in a clean,
dry place.
After the tap hole is drilled, the books recommend the use of a small mallet, with a wooden or
rubber head, is used to gently tap the spout into the drilled hole. We actually used a hammer,
but the bottom line is that It is very important not to use too much force when seating the tap, for
you do not want to split the sapwood and thus allow the sap to leak around the tap. Any
passerby would then see a dark stain running underneath the tap and know that an amateur
had tapped that tree and split the sapwood. I also learned that there is a greater danger of
splitting the wood when seating the spouts in colder weather. It is thus a good idea, if possible,
to tap the trees when they are not frozen, but if you must tap a frozen tree, do so with extreme
care so as not to split the frozen wood.
WHEN TO SET AND REMOVE THE TAPS
As noted above, maple sap will flow anytime when the weather conditions are right. The largest
and most consistent flows, however, occur in late winter and early spring during the months of
February, March, and April. Fall tapping is really not worthwhile because of typically low sugar
concentrations and shorter periods of sap flow. One of the main challenges in maple sugaring is
knowing when to tap. It varies from year to year and depends completely on the weather. If you
tap too late, you risk missing the important high sugar content of the early runs. If you tap too
early and you risk loosing both quality and quantity due to the micro organisms that eventually
start to grow in the holes. A condition referred to as "dry-hole" occurs when the micro organisms
proliferate to a point that the sap stops flowing completely.
Predicting when the sap will start to run is educated guess work at best. Just ask any
weatherman. First time maple sugarers may find that the most effective way to time their tapping
is to "tap when the experts tap." In other words, when experienced sugar makers in your area
start to tap, it is probably a good time for you to tap. Unfortunately I have not notice any sap
collection buckets along the country roads leading to Straight Creek. I simply wait for freezing
nights followed by warm days, and so far I seemed to have hit it right. My three sap flow seasons
have lasted about three week each. Perhaps I have experienced that age old phenomenon
known as beginner's luck.
Finally, when the sugar season has come to an end, it is time to remove the spouts from the
trees. They should be gently removed before the trees begin growth. Gentle removal will reduce
injury to the sapwood and assist the tree's ability to cure the tap wound. Spouts left in tap holes
during the growing season will interfere with closure and cause even more injury when removed.
Plugging tap holes after spout removal is also not recommended for the plug not only interferes
with tap hole closure, but again encourages the growth of disease spreading micro organisms..
SAP COLLECTION SYSTEMS
Large commercial maple syrup producers use complicated systems of tubing that lead directly
from multiple trees into large collection containers that are then emptied into larger tractor
transported containers that haul the sap to the sugar houses for evaporation. Small scale sugar
operations use collection containers that range from galvanized steel buckets with lids to plastic
gallon milk jugs. Typically, the buckets and jugs are hung right on the tap, but after I learned
about the hose collection systems of the big maple syrup producers, I thought that a
combination system would work well, and it did. I use plastic gallon milk jugs. I set the jug on the
ground next to the tree and connected it to the tap with an appropriate length of plastic tubing.
This way I do not need to worry about squirrels or wind knocking the jug off of the tap. I have
also used fifteen gallon food safe canisters with plastic hoses connecting the tap to the
cannister. The only difficulty with the fifteen gallon canister collection system was that fifteen
gallons of sap weighs about one hundred and twenty pounds, a hefty weight to maneuver up to
the evaporator! We could, however, let the sap collect in the larger fifteen gallon bucket all
week, without worrying about overflow.
There is one wonderful advantage with using plastic milk jugs for sap collection. The jugs are
fairly transparent and with a simple glance, you can tell if it is time to collect the jug or let it sit for
a while longer. Another milk jug advantage is that the gallon sized jugs can be used for both
collection and storage of the sap, as I did in my refrigerator as well as my neighbors. Still
working a city job, I have to wait for the weekend to boil the sap down into syrup. And finally, I
should not forget to mention that milk jug collection devices are a free perk of drinking lots of
healthy milk!
I should, however, give you a word of caution here. I will only leave the fifteen gallon canisters
out collecting sap if I know that the weather is going to stay fairly cold during the week. If the
temperature rises much above forty degrees the sap can go bad if left in the sun. It is really
quite important, once the sap has been collected, not to let it get too warm, for it will sour, much
like milk. The jugs of sap that I collect I place right into my refrigerator or set in the snow in a
shady outside place. They thus stay good and cold until I can boil them down that next
weekend.
HOW MUCH SAP MAKES HOW MUCH SYRUP?
Because the conversion of sap to syrup is essentially a concentration process, the initial sugar
content of the sap determines the amount of sap that will be required to produce a gallon of
syrup. There is a formula called the "Rule of 86" that is used to estimate the number of gallons
of sap of a specific density that will be required to produce one gallon of maple syrup. You just
need to figure out the sugar content of your sap with a hydrometer and then multiply that
number by 86 to come up with the number of gallons of sap needed to produce one gallon of
syrup. I have read of variations ranging between twenty to forty five gallons of sap, producing
one gallon of syrup. In short, a lot of water needs to be evaporated out of the sap in order to
produce maple syrup!
We tested the sugar content of our sap with a hydrometer purchased at a wine making supply
store. Our Straight Creek sap typically has a sugar content of 2.5%. We were quite pleased
with that. The hydrometer is really a very simple devise. It floats upright in a liquid and is
calibrated to test the sugar content at 60 degrees Fahrenheit. The hydrometer floats higher in
the liquid the higher the sugar content. You simply read the marking at which it floats and that is
your percent of sugar.
HEAT SOURCE/FUEL
Wood is the traditional fuel for heating maple evaporators, and it is still used by many
commercial producers. Most sugarers believe that the wood smoke adds a necessary ingredient
to the finished syrup taste. Wood is also the most economical source of fuel, particularly if one
has sixty three acres of farm land covered with trees, as we do at Straight Creek. A low
overhead maple syrup producer, such as Straight Creek Farm, can thus exchange the labor of
chopping the wood and feeding the fire for a capital investment in fancy evaporators, and the
operating expenses of a fossil fuel source of heat. The healthy labor involved in procuring the
wood and keeping a good fire under the evaporator is obviously free.
Statistics have been compiled by the Ohio Extension Office regarding the amount of wood
needed to produce one gallon of maple syrup. It takes approximately one full cord of firewood to
produce 25 gallons of syrup. For those of you who do not know, a cord is a stack of wood
measuring 4 feet high, 8 feet long, and 4 feet deep with a volume of 128 cubic feet. Actual
syrup production also depends on the efficiency of the evaporator, as well as the species of
wood burned. Other things being equal, the heavier or denser the wood, the higher its available
heat.
Table of approximate available heat in one cord of wood at 20% moisture content as cited by the
Ohio Extension Service
Species Millions of BTUs available per cord
Locust, Black 24.9
Hickory, Shagbark 24.9
Ironwood 24.6
Apple 23.9
Oak, White 23.2
Beech 21.7
Maple, Sugar 21.7
Birch, Yellow 21.3
Oak, Red 21.3
Ash, White 21.0
Ash, Green 20.0
Walnut, Black 19.5
Birch, Paper (White) 18.7
Maple, Red 18.7
Hackberry 18.7
Cherry, Black 18.7
Elm, Slippery (Red) 18.4
Sycamore 17.9
Elm, American 17.6
Ash, Black 17.2
Maple, Silver 16.5
Boxelder 16.2
Cottonwood 14.0
Willow, Black 13.6
Aspen 13.3
Basswood 12.5
It makes sense to become familiar with available wood species. Obviously a cord of a lighter,
less dense wood, such as sycamore, is not equal in heating value to a cord of the more dense
species, such as locust. We have both sycamore and locust at Straight Creek Farm, but we like
to save the locust for burning in the wood stove that we use to heat the cabin, for locust will burn
through the night. (We do not like to get up in the middle of the night to stoke the fire.) We thus
use the sycamore for maple sugaring, accepting the fact that the lighter, less dense sycamore
would have to be added to the fire more frequently to keep the evaporator pan at a boil. In short,
the lighter, less dense wood requires more labor during the evaporation process, but that is
alright. The labor kept us warm.
The wood used to fire an evaporator may be round or split, depending on its size, but should be
thoroughly seasoned or dried. Most hardwood species will require from 9 to 12 months to
thoroughly season. This means that wood used for sugaring should have been cut the previous
spring or summer. Wood cut later than this will have a higher moisture content and will thus burn
less efficiently because a portion of the heat will be used to evaporate the excess moisture
content in the wood. It is well known that firewood seasons most rapidly if it is placed off the
ground under roof, and is stacked in a way that encourages air to circulate between the logs.
We use one side of our old tobacco barn and stack our wood on locust runners set on the
ground. We separate the wood into rows of locust and sycamore, so that we can easily get the
wood we need for any particular fire purpose. We have also built a wood shed up by the cabin,
and our plan is to eventually move all of the wood out of the barn and into the shed, as soon as
time and motivation permit.
BOILING DOWN THE SAP
The basic premise of sap evaporation is to keep the sap at a constant rolling boil, adding more
sap as the water evaporates. The process simply involves adding new sap to the boiling sap
until the sap's two to three percent sugar content increases to sixty eight percent, at which time
the sap is no longer sap, but is maple syrup. As the water evaporates, the sugar content
increases. Syrup is produced as the sugars concentrate and the water content is reduced.
During the course of this evaporation process, the characteristic flavor and color associated with
pure maple syrup are produced, but it is not only a concentration of the sugar content that
produces maple syrup, for the compounds present in the sap also increase in concentration,
and it is these concentrated compounds that add to the color and flavor of pure maple syrup
with which we are all so familiar.
Because we are evaporating the water out of the sap, it stands to reason that the larger the
evaporation pan's surface, the quicker the water will evaporate and the sap will concentrate. I
used a stainless steel lasagna pan as my first evaporator pan, and a stainless line serving tray
as my second, but even a small pot would do. Using a pot would just take longer, for there
would be less surface area for the evaporation to occur. Most evaporator pans measure two by
three feet, and are six to eight inches deep. Even though the sap is usually boiled down at a
depth of three inches, the deeper depth of the pan is necessary. The sap tends to boil over as
it's sugar content increases. A boil over is imminent when the sap's surface starts to get small
white bubbles all the way across it and the bubbles start to rise up in the pan. Before you know
it, the sap is frothing over the sides in a sweet sticky mess. I have learned that simply removing
the pan from the heat source will stop a boil over, but it is often difficult to pick up a large pan of
boiling sap that can weigh as much as twenty four pounds. Another tried and true way to stop a
boil over is to drop a few drops of vegetable oil into the pan or else touch the surface of the
frothing sap with a stick of butter. Apparently the oil and butter somehow break the boil over
process, but I do not know, and could not find the chemistry behind this phenomenon. I will try to
figure it out and add what I learn to this page at a later date, but if any of our readers know,
please do share that chemistry with us.
Because the evaporation process involves constantly adding new sap to the boiling sap, it is
important to figure out a way to add the new sap without breaking the boil. If the boil is broken
by adding cold sap, more time will be required to reach the final syrup, as more time will be
required to bring the sap back up to that rolling boil. Maple sugarers have thus developed the
concept of preheating the sap before it is added to the evaporator pan. There are many forms
of preheaters, but all involve the same basic principle of heating up cold sap before adding it to
the boiling sap so that the boil is not broken. Commercial sugarers use systems of tubing that
warm the sap with the evaporating steam, but our preheating system at Straight Creek Farm was
extremely simple. We just used a coffee can that we perched by the side of the lasagna pan.
We periodically ladled cold sap into the coffee can and allowed it to trickle out of a hole at the
bottom of the coffee can into the lasagna pan below. We adjusted the trickle rate with a wooden
stick that Greg carved so that the rate of flow could exactly equal the rate of evaporation. Thus
we simply had to ladle cold sap from our fifteen gallon buckets into the coffee can as the coffee
can emptied.
There is one final note of importance here. Do not use aluminium pans for the boil down
process. The aluminum oxidizes and taints the syrup. Steel seems to be the material of
preference for sap evaporators.
So how do you know when you have finally boiled off enough water and have ultimately arrived
at maple syrup? You could test the syrup with a hydrometer, after it cools down to 60 degrees
Fahrenheit, and when it reaches that magic sixty eight percent sugar content, you know that you
have syrup. This can be time consuming, however, and as the sap continues to boil while you
are waiting for the test sample to cool, you might over boil the syrup and end up with hard rock
maple sugar candy! Thus, the better process is to test the temperature of the sap with a candy
thermometer. When the temperature of the boiling sap reaches a temperature of 7.2 degrees
Fahrenheit above the boiling point of water on that particular day at that particular location, then
you have maple syrup. To be precise, you should boil a pot of water and test the temperature at
which it reaches a rolling boil. The boiling point on any given day depends on barometric
pressure, thus weather and topographic elevation are the two factors that determine an exact
boiling point. The approximate average boiling point of water is 112 degrees Fahrenheit. By the
end of my first three seasons of sugaring I must confess that I have usually been a bit tuckered
out. Rather than boil water and measure the temperature at which it reached a rolling boil, I
have simply boiled my sap until it reaches a temperature of 220 degrees Fahrenheit. And guess
what? For three years in a row I have ended up with delicious tasting maple syrup!
SYRUP FILTRATION
When maple syrup finally reaches it's syrup stage, it contains some solid particles, that look like
dark specs floating in the syrup. These specs are technically called "niter" and are commonly
called sugar sand. Sugar sand is the product of boiling down the calcium and magnesium salts
found in the sap's malic acid, one of the organic acids present in maple sap. These salts form
during the evaporation process. They actually crystallize out of the sap solution because they
are less soluble than the sugar as the concentration of sugar increases. Because the syrup is
quite thick, the sugar sand tends to float suspended in the syrup and if left in the syrup, it can
give the syrup a gritty texture.
The amount of sugar sand varies from batch to batch of maple syrup. It will also vary from year
to year as well as during the season and will even vary from one sugar bush to another within
the same season. The reasons behind this variation are not really known, but must depend on
the amount of mineral compounds found in the maple sap. Apparently soil conditions as well as
weather and site specific conditions, all contribute to the amount of minerals found in a batch of
sap.
To get the sugar sand out of the syrup requires filtering. I found a variety of commercial filters
on the internet, but for my first batch of syrup I simply used coffee filters. The hot syrup dripped
slowly but surely through the filters, but as the syrup cooled, the filters became impenetrable.
Thus I had to heat the remaining syrup back up and run it through a new filter. This system
worked, but was far from perfect. For my second sugar season I ordered felt filter cones that
are specifically intended for syrup filtering. They have worked great and after use can be
washed out and used again.
HOT PACKING
To prevent the contamination of finished syrup by yeast or mold growth, finished syrup should
always be bottled while hot. If the temperature of the syrup after filtering is 180°F or higher it
can be bottled immediately. If ,however, the syrup has cooled and the temperature has fallen
below 180°F, the syrup should be reheated to 180°F or slightly higher. I learned, however, that
the syrup should not be reheated to temperatures of 200°F or higher, because this higher heat
will cause the syrup to darken and loose flavor. It is important to bottle the syrup at temperatures
over 180°F, because those temperatures will kill any yeast or mold spores present in the bottle.
It is also important for the entire inside of the bottle to be exposed to this 180°F temperature.
This is done by simply turning the bottle over and letting the syrup coat the entire inside of the
bottle, cap and all, before it is set aside..
ENJOYING MAPLE SYRUP
Now it is time to sit back and enjoy our maple syrup. Try a new recipe for a maple syrup basted
pork roast. Or simply prepare dinner biscuits topped with butter and 100% pure maple syrup.
And of course, don't forget pancakes or waffles smothered in maple syrup. No doubt it all tastes
good, but I also know that it all tastes especially good because we know that we have made the
maple syrup ourselves from trees that we have grown to know and respect in a very unique
way. Maple syrup really is the condensed energy of the trees sweetly crossing your lips and
lightening up your heart. Each taste is priceless! Enjoy!
back to Maple Sugar at Straight Creek Farm,
Straight Creek Valley Farm