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1
Maple sugaringand the science of sap flow
Photo by: Paula Murakami
What makes this possible?
The Science of Sap Flow and Maple Syrup Production
2
Basic physiology of maple sugaring
Maple syrup production possible - 2 unique
properties of maple trees:
Ability to generate positive pressure in xylem sap
(Allows sap to flow)
The high sugar concentration in spring xylem sap
Basic physiology of maple sugaring
Must also have the right weather
conditions for sap to flow!
Freezing nights followed by warm days
Phloem
Photosynthate (sugar) from
source to sink
Xylem
Water from soil to leaves
(usually not sugars!)
3
Xylem Sap sugar
Air temperature
Mar 1Jan 1 May 1Nov 1
Sugar maple cross section
Vessel
Ray cellscontainingstarch
Fiber cells
The sap flow mechanism in maple:
Freezing and thawing temperatures are required
4
Freezing causes liquid to expand
Why doesn’t sap exude during a freeze and shrink during a thaw?
Vessel
Ray cells containing starch
Sugar maple wood section
Fiber cells air filled in
maple
Vesselwith sap
Air-filledfibers
Temperature:Above freezing
for hours or days
5
Vesselwith sap
Air-filledfibers
Ice crystal growth (frost) occurs inside the air-filled fibers as the branches freeze. The water is supplied by the sap in the vessels.
Vesselwith sap
Air-filledfibers
Temperature: Falling from above freezing to
just below freezing
Generates (−) pressure
Vesselwith sap
Air-filledfibers
Temperature: Below freezing
for several hours or days.
6
Vesselwith sap
Air-filledfibers
Temperature:Rising from below to above freezing.
Generates (+) pressure!
Sap pressure 25-30 psiSap pressure 0 to -5 psiSap pressure 10 psiSap pressure 2 psiSap pressure -5 psi
Tem
per
atu
re (
o C)a
nd
Pre
ssur
e (p
si)
-5
0
5
10
15
20
25
30
-5
0
5
10
15
20
25
30
March 21
Pressure
March 20 March 22
Branch temperature
Temperature and pressure in the spring in untapped trees
But why does sap flow when we put a hole in the tree?
7
Sap
Air pressure = 0 psi
Sap pressure = 15 psi
Atmospheric pressure lower than inside the tree ~ sap flows out of the wound!
Figure by: Tim Wilmot
Maple syrup production
Sap collection
Photos by: Brian Stowe
8
Sap collection
Trees are tapped with cordless drills and plastic spouts are most common
Photos by: PMRC
Sap collection
Photos by: PMRC
Sap collection
Network of 5/16” plastic tubing
connects to larger ‘mainlines’
9
Sap collection
Sap flows from the network of mainlines into the sugarhouse
Sap collection
Many producers add vacuum to their tubing
systems
Adding vacuum
Air pressure = 0 psi
Sap pressure = 15 psi
Vacuum (15”Hg) = -7.5 psi
Figure by: Tim Wilmot
10
Filtering
Solid material
MicroorganismsAfter sap is removed from lines it is often filtered by UV light
Photo: Tim Wilmot
Sap storage
Sap is stored in large tanks for as short a time as possible
Photo by: PMRC
Reverse osmosis
Raw sap is ~2% sugar
RO concentrates sap (8-10%) without
heating
Reduces:Evaporator fuel costs
Boiling time Photo by: PMRC
11
Reverse Osmosis
% Sugar
Boiling
EvaporatorsMany types
Fuel typesWood
OilPhoto by: George Cook
Evaporator basic anatomy
Front Pan
Back Pan
12
Evaporators
Back panWhere sap comes in
Deep flues facilitate heat transfer
From 2-~8%
Back PanSap inlet
Syrup Drawoff
Front Pan
Front panWhere syrup is made
Several compartments
From 8 to 65%
Back PanSap inlet
Syrup Drawoff
Front Pan
Evaporators
Boiling
Syrup Draw-off
13
Finishing
Get to appropriate density before
packing
If too high:Crystallization
If too low:Fermentation, mold,
bacteria…
Photos by: Tim Wilmot
Filtering and packing
Syrup must be filtered to remove solids and make a clear product
Photo by: Brian Stowe
Filtering and packing
Filtered syrup is hot-packed into drums or smaller containers
Photos by: PMRC
14
Grading
Syrup is graded on four criteria:
Color
Flavor
Density
Clarity
Color is primary determinant, but all syrup must meet the other standards, too
Photo by: Mark Isselhardt
Grading
Different grading systemsVT
US
Canada
Different names, but similar standards
Only pure VT syrup can be labeled as VT syrup with a VT grade
Photo by: Mark Isselhardt
Color Grading
Based on % light transmittance (at 560nm)
Temporary Grading KitsGrading ‘meters’
‘Permanent’ Grading Kits
Photos by: Mark Isselhardt
15
Density
66.9% minimum in VT
Hydrometers
Refractometers
Photos: PMRC
Vermont Maple Syrup Grades
~ Vermont Fancy ~ Light amber color and adelicate maple bouquet.A mild maple flavor,excellent on foods suchas ice cream whichpermit its subtle flavor tobe appreciated.
~ Grade A Medium Amber ~
Medium amber color anda pronounced maplebouquet. Characteristicmaple flavor, that ispopular for table and allaround use. Great onpancakes and frenchtoast.
~ Vermont Grade B ~ The strongest anddarkest grade of maplesyrup. Primarily usedfor cooking and alsopopular for the table.Makes a great substitutefor other sugars inbaking.
~ Grade A Dark Amber ~Dark amber color and arobust maple bouquet.This hearty maple flavoris very popular for tableand all around use. Isoften used to add flavorwhen cooking.
16
University of VermontProctor Maple Research Center
Underhill Center, Vermont
Department of Plant Biology,
College of Agriculture & Life Sciences
Proctor Maple Research Center
Maple research conducted at UVM since 1890s
PMRC established in 1946
Photos: PMRC
UVM Proctor Maple Research Center
SapShed
PMRC Lab
Martin Block(High Yield Study)
RedSeries
(Strategies Study)
Main Bush(EquipmentComparison
Study)
*
Sugarhouse
**
N
17
UVM Proctor Maple Research Center
Mission:Maple Research
Extension/OutreachDemonstration
Current Research at PMRC
Maximizing Sap Yield
Typical yield much lower than maximum attainable:
<0.2 – 0.4 gal/tap (buckets→vacuum tubing)
vs.
0.5++ (ideal conditions)
1. Increasing productivity and profitability of maple syrup production
Innovations to Maximize
Sap Yield
18
1. Increasing productivity and profitability of maple syrup production
Birch Syrup Production
in maple operations
Existing equipment, trees, and infrastructure
Valuable ($) product
2. Environmental and management impacts on the maple resource
Sustainability of maple syrup production depends on healthy trees
Impacts of increased carbohydrate extraction on tree health
Reassessment of tapping guidelines
Describe and mitigate effects of climate change on maple syrup
production
3. Maple syrup chemistry and quality
Descriptive chemistry
Maple syrup contamination, adulteration, legal issues
Impacts of processing technologies on maple
syrup chemistry and flavor
19
3. Maple syrup chemistry and quality
Integrity of maple syrup characteristic attributes is
essential!
Technology rapidly evolving, effects of new
technologies often untested
RO, Air injection, etc.
Impacts of processing technologies on syrup chemistry and flavor
What are the effects on syrup chemical composition and flavor?
3. Maple syrup chemistry and quality
Controlled experiments to test impacts of
technologies on syrup quality:
Chemical composition
FlavorUVM Maple Production Research Facility
Impacts of processing technologies on syrup chemistry and flavor