June 1972

MAPLE SIRUP PRODUCTiON FROM BIGLEAF MAPLE

by Robert H. Ruth, J. Clyde Underwood,1/Clark E. Smith, and Hoya Y. Yang-

ABSTRACT

Bigleaf maple sap flow during the 1970-71 season rangedfrom none to 16.9 gallons per taphole and sugar content ofthe sap from 1.0 to 2.6 percent. Sugar content also variedseasonally, with the sweetest sap flowing in late January.The sirup was very flavorful, although not as strong in typicalmaple flavor as that made from eastern sugar maple. Sirupproduction appears quite feasible as a hobby. The possibilityof commercial production should not be ruled out as additionallocal experience is gained.

Keywords: Maple sugar, bigleaf maple, Acer macrophytllum,sap.

‘Rober t H. Ruth and Clark E. Smith arePrincipal Silviculturist and Forestry Research Tech-nician, respectively, Pacific Northwest Forest andRange Experiment Station; J. Clyde Underwood isHead, Maple Investigations, Eastern Marketing andNutrition Research Division, Agricultural ResearchService; and Hoya Y. Yang is Associate Professor,Food Science and Technology, Oregon StateUniversity.

lNTRODUCT/ON

Maple sirup has been made fromthe sap of bigleaf maple ( Acermacrophyllum ) on numerous occasions(1, 2, 9), but we find no record ofcommercial sirup production. Thiscontrasts with the large maple sirupindustry developed around the sugarmaple ( Acer saccharum ) of the north-eastern United States. Recent workwith sugar maple is resulting in in-creased sap flows, greater efficiencyin handling and processing, and bettercontrol of flavor. The exploratorystudy reported here was undertaken toevaluate sap flow characteristics ofbigleaf maple and the quality of bigleafmaple sirup. In addition, we hoped togain an initial insight into the economicfeasibility of maple sirup production inthe Pacific Northwest.

Bigleaf maple is the largest andmost valuable western maple. Itsrange extends from the mountains ofsouthern California, northward throughthe western parts of Oregon, Washing-ton, and British Columbia almost tothe southern tip of Alaska. It growson a variety of soils, but best growthis on deep alluvial soils near streams.Occasionally pure stands are found,but bigleaf maple generally occurssingly or in small groups. Maturetrees average about 50 feet tall and 18inches in diameter. Growth is rapidfor the first 40 to 60 years, withmaturity reached at 150 years or more.Bigleaf maple is a tolerant species,especially when young, and frequentlyis surrounded by taller conifers ( 4).

Past experience with bigleafmaple in the Pacific Northwest hasshown an annual sap flow of 3 to 6gallons per tree, with about 35gallons of sap required to make 1gallon of sirup. Using the “Rule of86” formula

66 = Gallons of sap toSap sugar content, % make 1 gallon sirup

the sugar content of the sap must havebeen about 2.5 percent. This approxi-mates the general average for sugarmaple (20).

Experience with eastern sugarmaple has shown that sap flow iscorrelated with cool nights when tem-peratures drop to 34o F. or lower,followed by warming conditions up to40o to 50o F. the next day. The east-ern sugar bush has a continental cli-mate with prolonged periods offreezing weather, and sap flow isdelayed until warming trends occurin the spring. Our study area has amild climate with frequent warm days.Sugar weather depends on occurrenceof cold nights, which may occur almostanytime during the winter. Steele 2/found that trees producing well at thebeginning of the sap-flow season con-tinued for that season and tended tobe good producers in subsequentseasons. Similar results have beenreported for sugar maple ( 6, l0).

‘Robert W. Steele. Final summary report of themaple sap study at Wind River. USDA Forest Serv.In service Rep., 6 p. (unpublished). 1948.

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In contrast to an eastern sugarbush, our study area has little soilfreezing. Annual precipitation isabout 40 inches; mostly falling aswinter rain. Soil moisture appearsreadily available for uptake by treeroots during the entire sap-flow season.Based on 12-year records near thestudy area, most bigleaf maple leaveshave fallen by October 28, and budsbegin to burst about March 23. Thesap-flow season for bigleaf maple istapering off about the time it beginsin an eastern sugar bush.

Tapping and Sap Collection

On November 17, 1970, about2 weeks after leaf fall, we tapped 13bigleaf maple trees ranging in sizefrom 12 to 30 inches diameter breasthigh gro

- 3 /wing under a variety of condi-

t i ons 3 Five were in a mixed standof maple, Douglas-fir ( Pseudotsugamenziesii), grand fir ( Abies grandis),and red alder ( Alnus rubra) (fig. 1).The others were in a cutting area wherall the conifers had been removed.These essentially were free of compa-tition in the overstory, but there wasa vigorous brush understory. Weselected the healthier, full-crownedtrees, although some had sustainedtop damage in past years. Samples ofsix trees showed an age range from78 to 183 years.

3 The authors gratefully acknowledge permissionto tap maple trees on property owned by StarkerForests, Philomath, Oregon, and School of For-estry, Oregon State University, Corvallis, Oregon.

e

Figure 1 .-Bigleaf maple tree surrounded bytaller conifers.

Initially, 11 trees were tappedwith one taphole and two of the largertrees with two, for a total of 15. Tap-hole diameter was one-half inch anddepth, 2-l/2 to 3 inches. Metal sapspouts were sterilized in anautoclave,and a germicidal pellet containing250 milligrams paraformaldehydewas inserted in each taphole to retard

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microbial action. Rubber rain guardswere placed around the spouts to pre-vent rainwater coming down the stemfrom running into the plastic sap col-lection bags (fig. 2). A supplementaltest comparing flow from old and newtapholes was carried out on threetrees January 25 to February 8. Con-sequently, on February 8, old tapholeswere abandoned in the remaining treesand new tapholes tapped about 6 inchesaway.

Two trees were completelyabandoned on January 18 as nonpro-ducers. Six new trees were added atthis time. Five were bored with onetaphole and one tree with two tapholes.Sap collections were continued atabout weekly intervals until bud burst-ing began in the spring.

Laboratory Brix readings were takenon the pooled sap from each collectiondate and used to evaluate seasonalchanges in sugar content of the sap.

Sap Processing to Sirup

The sap was concentrated tosirup in 2- to 20-gallon, steam-jacketedstainless steel kettles. The steampressure was 55 pounds per squareinch. Large batches of sap were con-centrated in larger kettles first andthen transferred to smaller kettles forfinal concentration. Most sap was pro-cessed immediately after collection fromthe field, but some was stored in a coldroom at 33” F. for up to 24 hours.

The sap was brought to boilingquickly; then the heat was reducedto maintain a gentle, steady boiling.Scorching of sirup was at a minimum.The foam formed during the earlypart of the boiling was skimmedcontinuously. The finishing pointof the sirup was determined with alaboratory refractometer. Althoughattempts were made to finish thesirup at 65o Brix, it was difficultto be precise because small quanti-ties of sirup permitted rapid changesin Brix readings.

U. S. Weather Bureau observa-tions at Corvallis, Oregon, about 5miles distant and at about the sameelevation, were used to characterizeconditions at the study area.

A portable refractometer wasused in the field beginning December16 to approximate the sugar con-tent of the sap in degrees Brix4/from each taphole at each collection.The average Brix reading from eachtaphole was used to compare sweet-ness of the sap among the trees.

‘Same density as a solution containing a per-centage of sugar numerically equal to the Brixvalue. The density of sap is due to a mixture ofsugar and small amounts of other dissolved solids,and the refractometer does not distinguish betweenthe density due to sugar and that due to othersolids.

In contrast with the steamkettle method available here, com-mercial procedure with sugar maplesirup involves rapid boiling inlarge, shallow evaporators. Thismethod brings out a better flavorthan that attainable with small-scalelaboratory procedures.

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Figure 2.-Bigleaf maple trees tapped for sap collection. A, Metal sap spout. Therubber rain guard prevents rainwater from running into the sap bags. B, Methodused to collect sap from sap bags.

Laboratory Analyses

Samples of sirup from eachcollection were sent to the EasternMarketing and Nutrition ResearchDivision of the Agricultural ResearchService at Philadelphia for evaluationby their Maple Investigations Group.The sirups were filtered through amedium-porosity, fritted-glass filterto remove the “sugar sand. ” Samplestoo small for filtration were let standin test tubes until they clarified bysedimentation. As the size of manyof the samples, especially those fromthe December runs, was too smallfor a complete analysis, variousconstituents and physical constantswere run on selected samples in sucha manner that a general evaluation ofthe season’s sirup could be made.Acidity values were determined withan in-line pH meter. Conductivityconstants were measured with a

Wheatstone bridge according to theofficial method of the Association ofOfficial Analytical Chemists (AOAC)(3 ). Brix readings were made witha hand refractometer. Ash contentwas determined by the official methodof the AOAC. The invert sugar valuewas by the Berlin method accordingto the AOAC. Flavor ratings weremade by the members of the MapleInvestigations Group.

RESULTS

Sap Flow

Sap started flowing right aftertapping on November 17, increasedbetween December 4 and 7, continuedto flow intermittently at a somewhatlower level through January 21, thentapered off rapidly in late January inspite of apparently favorable sugarweather (fig. 3). This reduced sap

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70-

:---

r---

I

I ,SuPP~:E;yrAL

f

I I I I I I I -

1 II I 7 10 16 21 I 4 1821 25 8 11 16 22

DECEMBER JANUARY FEBRUARY

Figure 3.-Average daily bigleaf maple sap ffow per taphole. Basis 15 tapholes tapped November 17, 1970; new taps February 8, 1971.

flow led us to suspect microbial activity or some other problem in the tapholes and prompted the supplemental test comparing flow from old and new tap- holes in the same tree. Sap flow from the new tapholes in this supplemental test was excellent. New tapholes tapped February 8 began to flow immediately and the sap volumes measured for the February 8-11 period were the highest of the season. This was followed by several heavy flows through March 8.

The new trees tapped January 18 produced high sap flows January 18-21 and February l-11 (fig. 4). Flows from all trees tapered off in mid-March and only a trace of sap flowed after March 22. Bud bursting was about March 29.

Total 1970-71 season sap flow per taphole for trees originally tapped November 17, 1970, ranged from zero to almost 17 gallons (table 1). Similar

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wide variation occurred among the seven tapholes in trees added to the study January 18. Sap flow from these trees ranged from 1.2 to 7.9 gallons per taphole. During the study, we collected 132 gallons of sap and made about 1.8 gallons of sirup.

During the sap-flow season, there were over 40 nightly minimums below 32” F. followed by daily maxi- mums above freezing (fig. 5). Mini- mum soil temperature measured at 4-inch depth in the mineral soil was never below 33” F.

Sugar Content

Sweetness of bigleaf maple sap varied among individual tap- holes from 1.0 to 2.6 degrees Brix (table 2). Average sap sweetness varied during the season with a peak of 1.4 degrees Brix reached about January 25 (fig. 6).

JAI

,

25 1

1 b 11 Ib I

22 i B I I

15 22 ARY FEBRUARY MARCH

Figure 4.-Average daily bigleaf maple sap flow per taphole. Basis 7 tapholes tapped January 18, 1971.

Table I.--Total bigleafmaple sap flow per taphole, 1970-71 season, trees originally tapped November 17, 1970

Taphol F/ number- "$;:a' / :zFs 1 Total

------- Gallons - - - - - - -

Zi6.28 Y9.93 16.21 274.08 2112.82 16.90

1.30 318.29 9.59 1.78 1.04 2.82

4/6.09 .54 6.63 .74 Y7.53 8.27

1.65 2.93 4.58 1.36 6.30 7.66

513.81 5.26 9.07 2.32 3.43 5.75

-- .31 .31 .25 .66 .91 -- -- --

2.4; 12.05 14.5;

Total 32.13 71.09 103.22

11 Srackets indicate tapholes in same tree.

21 Sap bag vandalized and 1 collection lost. 27 Sap volume from supplemental study included.

41 Sap bag overflowed on 1 occasion.

5/ Abandoned January 18.

Sirup Quality

Results of laboratory tests on bigleaf sirup are shown in table 3. Analysis was same as that for com- mercial maple sirup. Typical values for a good commercial sugar maple sirup also are shown. These include a low invert sugar content and an average color toward the lighter end of the scale--reflecting recent quality improvements. The bigleaf maple sirup was concentrated in steam kettles, and this procedure is not equivalent to the commercial open-pan evaporator, where the intense heat brings out more flavor. The flavor comparison, therefore, is approxi- mate.

Although the bigleaf maple sirup was very tasteful, all the samples were low in typical sugar maple flavor. This low level of the usual predominant flavor allowed other flavors to be identified. One was a detectable but not too objectionable varnishlike taste in some of the late-season samples. To determine the effect of additional heat, selected samples were auto- claved for 30 minutes at 15 pounds per square inch, but this did not improve the flavor. Rather, the Varnish taint” was increased in those late season samples that had it. The color of the Oregon sirup was dark for a product concentrated in steam kettles, and this does not correlate with the low value for invert sugar. Research has shown that color is proportional to the invert sugar in the sirup; the higher the invert, the darker the six-up (5).

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A

Table 2 .--Sweetness of bigleaf maple sap from individua2 tapholes

Taphole number-L/

Sap sweetness

OBPiXY

L' Brackets indicate 2 tapholes in 1 tree.

/ Approximately equal to percent sugar content.

The pH of eastern maple sirup is normally just above 7. The Oregon sirups were significantly more acidic, ranging from 4.9 in December to 6.9 for later season sirup. This may ex- plain the lack of a typical maple flavor. Sap from sugar maple is slightly acid (pH 6.5 to 6.9), but as soon as it begins boiling it becomes alkaline, often reaching a pH of 9 ( 5 ). This alkaline condition is necessary for development of good maple flavor.

The ash content and conductivity values of the bigleaf maple sirup were both much higher than for normal sugar maple sirup. As the conductivity of the sirups is due to their salt content, these two values should and did parallel one another. The high values for the western sirup may reflect the rela- tively low sugar content of the bigleaf maple sap. It has been noted with all types of maple trees that sap with low sugar content produces high ash sirup due to the greater concentration needed to produce standard density sirup.

Table 3 .--QuaZity comparison between bigZeaf maple sirup and a fancy number 1 sugar maple sirup

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Determinatiodi Bigleaf maple

Number of Sugar maple

samples Average Range range

Ash percent PH Conductivity Invert sugar percent Color grad&/ Eastern sugar maple

flavor

6 10 9 2

18

18

3.3 2.0-5.5 0.5-1.1 6.3 4.9-6.9 6.9-7.2

630 476-885 105-158 0.32 0.31-0.32 0.25-2.30 B A-C AA-A

Poor Fair-poor Excellent- good

y On sirup with 66 percent solids.

g1 USDA standards.

Sap production of bigleaf maplemay vary widely from year to year, asit does with eastern sugar maple, andthe 1970-71 season studied here mayprove to be above or below average.Assuming 1970-71 to be an averageseason, we conclude that sirup produc-tion from bigleaf maple appears fullyfeasible as a hobby.

Several approaches have thepotential for greatly increasing pro-duction. The slowdown in late Januarycould have been avoided by boring newtapholes sooner. A still more efficientapproach might be to delay boring anytapholes until early December, thusavoiding the early season period of lowsap flows. The same would apply tolate flows in the spring. Collectionscould have been terminated in earlyMarch. This decision should be basedon local freezing-thawing cycles, whichwill vary considerably within the rangeof bigleaf maple.

Production can be increased byfinding new trees to replace lowproducers. Three of our original tap-holes produced over 14 gallons of sap,even though the original tapholes wereused too long, some sap bags over-flowed, and some bags were vandalized.One hundred tapholes like these threeshould provide about 1,500 gallons ofsap. Assuming an average Brix valueof 1.5, this would make about 26 gallonsof sir-up. Two of these three highproducers were intermixed with coni-fers, indicating that such trees indeedshould be considered in searching for

the best trees. However, experiencewith sugar maple is that open-growthtrees produce more and sweeter sapthan trees growing under crowdedconditions.

Additional production shouldcome from selection of trees with highsugar content. There was consider-able variation among the study trees,with sap from one taphole containing2.6 percent sugar, more than twicethe average of the other trees. Thetree with this taphole was growing inthe logged-over area. Many sugarproducers in the East believe it doesnot pay to process sap which tests lessthan 1.5 percent. Availability ofinexpensive fuel in the West may reducethis somewhat, but possibilities ofcommercial production will be greatlyenhanced if sweeter trees can be found.The low sugar content of early and lateseason sap flows is further argumentfor limiting sap collections to themain part of the sap-flow season.

Besides placing of germicidalpellets in the tapholes, two additionaltechniques developed with sugar mapleoffer possibilities for increased effi-ciency and further increases in sapproduction. One is the use of flexibleplastic tubing for collecting sap. Thetubing is connected directly to sapspouts so the sap will run by gravitydirectly into large collection tanks. .This system eliminates the need fora large labor force to collect sap andpermits one- to two-man operationsto handle 1,000 or more taps. Thesecond is the use of vacuum pumpingon an unvented tubing system to

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increase sap yields. Fourfold in-creases in sap flow have been reportedin some studies (7). To our knowledge,neither technique has been tried withbigleaf maple.

If the above approaches do in-deed lead to production increases,commercial production may bepossible. The scattered distributionof bigleaf maple trees will always bean obstacle to efficient production.The best opportunities will be inoccasional pure stands or wherenumerous trees are accessible alongall-weather roads. The compositionof bigleaf maple in a stand can beimproved by thinning the other species,and, of course, pure stands can bedeveloped by planting.

Standard practice in the Eastis that sap must not remain in thebuckets or sap bags more than a fewhours before it is collected; otherwiseit will ferment and spoil (10). Wewere not able to visit the study areafrequently enough to follow this prac-tice, and some sap remained in bags

a week or more. No sign of fermen-tation was noted. Perhaps micro-organisms in the sap were killed bysolar radiation transmitted throughthe sap bags (8). On the other hand.this delay may have adversely affectedthe flavor of the sirup.

In any event, the quality of thesirup made from the bigleaf mapletrees in this study was lower thansirup from the sugar maple, beinggenerally comparable to sirup madefrom eastern soft maples, such asred and silver maple. The sap fromthe soft maples, like the bigleaf maplesap, often is low in sugar content.Some of the bigleaf samples did havea trace of an unfamiliar “varnish”taste, but this was not too objection-able. It occurred only in late-seasonsap collections which may not warrantcollection anyway because of low sapflow. With experience in collectingand processing bigleaf maple sap,procedures surely will be found tomake a good, marketable sirup,even if its flavor may be differentfrom that of sugar maple.

1. Anonymous1947. Hillside farmer-pastor expert with sap auger. The Sunday

Oregonian Farm-Home-Garden sect. LXVI(4): 1, 10(January 26, 1947).

2. Applegate, Jesse A.1930. Recollections of my boyhood. 1n The Oregon Trail and some

of its blazers, by Maude A. Rucker, p. 192-193. New York:Walter Neale.

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3. Association of Official Analytical Chemists1970. Official methods of analysis of the Association of Official

Analytical Chemists. 11th ed., sect. 31: 176.

4. Fowells, H. A. (comp.)1965. Silvics of forest trees of the United States. U.S. Dep. Agric.

Handb. 271, 762 p., illus.

5. Hayward, F. W., and C. S. Pederson1946. Some factors causing dark-colored maple sirup. New York State

Agric. Exp. Stn. Bull. 718, 14 p. Geneva, N. Y.

6. Koelling, Melvin R.1968. Sap yields from fall and spying tapping of sugar maple. USDA

Forest Serv. Res. Pap. NE-115, 8 p., illus. Northeast.Forest Exp. Stn., Upper Darby, Pa.

7. Barton M. Blum, and Carter B. Gibbsv:1968. A summary and evaluation of research on the use of plastic

tubing in maple sap production. USDA Forest Serv. Res. Pap.NE-116, 12 p., illus. Northeast. Forest Exp. Stn., UpperDarby, Pa.

8. Naghski, J., and C. 0. Willits1953. Maple sirup. VI. The sterilizing effect of sunlight on maple sap

collected in a transparent plastic bag. Food Technol. 7: 81-83,illus.

9. Pacific Power and Light1963. Tasty syrup from native maple trees. Pac. Power & Light

Farm News No. 1, 2 p., illus.

10. Willits, C. 0.1965. Maple sirup producers manual. U.S. Dep. Agric. Handb. 134,

112 p. , illus.

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