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Maple sugaringand the science of sap flow

Photo by: Paula Murakami

What makes this possible?

The Science of Sap Flow and Maple Syrup Production

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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!)

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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

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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

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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.

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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?

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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

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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’

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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

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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

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Reverse Osmosis

% Sugar

Boiling

EvaporatorsMany types

Fuel typesWood

OilPhoto by: George Cook

Evaporator basic anatomy

Front Pan

Back Pan

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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

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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

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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

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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.

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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

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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

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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

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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