Progress report for FNC23-1372
Project Information
I am the owner of the Rusted Flatbed Farm, a 13-acre leased urban agroforest on the southeast side of Indianapolis, Indiana. In the early 1900s the land was pasture with a sugarbush. Midcentury overgrazing killed the sugarbush, and the forest has slowly regenerated. The trees are quite diverse, predominantly sugar maple and black walnut, but also tulip poplar, elm, hackberry, box elder, black locust, sycamore, paw paw, and cottonwood.
I began operating the farm over the last five years. I have hand-cleared the understory of grapevines and invasive species such as Asian honeysuckle, Russian olive, and flora rose. I have planted native species including a plantation of 180 black walnut saplings, as well as pecans, and hazelnuts. I harvest wild blackberries, morels, and paw paws. In 2021 and 2022, I began maple syrup production, tapping 40-50 trees and bottling 6-9 gallons of maple syrup.
I am a lifetime member of the Indiana Nut and Fruit Growers Association, a board member of the Indiana Maple Syrup Association, editor of The Tapline, and an advisory member of the Purdue University Acer Grant Program promoting Indiana maple syrup. I have a background in law and politics.
Black walnut syrup is a natural and sustainable locally-grown sweetener. Its flavor is comparable to maple syrup, but nuttier, and commands a substantial premium over maple syrup: ($10-$15 for 2 ounces of black walnut versus a pint of maple syrup). Making black walnut syrup is more difficult than maple syrup because black walnuts produce less sap and have lower sugar content. Forest owners are also hesitant to tap black walnuts with timber value. This may create a niche for urban agroforests that value preservation over timber harvesting, and a productive use for trees without commercial timber value.
Unlike maple syrup, little research has been published for black walnuts. One of the few sources of data on black walnut tapping is a recent study by Future Generations University through a 2019 SARE grant. It indicated that black walnut trees should be tapped later in the season, they may require differently shaped taps, and vacuum tubing could quadruple sap collection. Correlations in the data regarding productivity and tree size, age, and location were inconclusive. Until a body of research is created documenting the results of black walnut tapping, optimal black walnut tapping practices cannot be established with any certainty.
The best way to understand how black walnuts are similar or different from maples is through a parallel tapping of maples and black walnuts at the same time and at the same location. This will provide evidence of the degree to which black walnuts production of sap follows or diverges from maples, and whether best maple practices should be followed in tapping black walnuts.
The solution proposed in this project is to increase the body of research on black walnut tapping by sustainably collecting and processing black walnut sap in tandem with maples and compiling data from each step in the process.
Timeline:
- May-December 2023: Sourcing and assembling equipment, selecting trees, mapping tube lines.
- January-April 2024: Tapping, boiling, and compiling data.
- May-August 2024: Draft article on findings and conclusions with assistance of grad student.
- September 2024: Circulate article among interested organizations; invitations to Field Day.
- October 2024: Field Day, survey.
- November-December 2024: Draft and submit report on grant.
This project will tap approximately 60 black walnut trees and 60 maple trees. Around 40 of each tree type will be tapped with vacuum tubing and 20 will be tapped with buckets. Tapping on both trees will begin at the same time (in Indiana, maple season starts in late January or early February). The trees will be numbered and trunks measured. Trees on buckets will be measured daily for sap production and sugar content. The bulk tank for the trees on tubing will be measured daily for sap production and sugar content. A spreadsheet with these measurements will be maintained, and daily high and low temperatures will be noted. Sap production for the maple trees will be noted as well. Daily fail rates of taps will be noted. Adjustments to tubing vacuum pressure, types of taps, and re-tappings will be tracked. After 3 weeks, bucket taps will be checked daily for the degree of closing of the taphole. Hours expended in labor will be tracked.
The walnut sap will be boiled as sufficient quantities are collected. For each session, the amount of sap, the rate of boil, and quantity of pre-filter final product will be recorded. The sap will be processed with industry-standard high-efficiency equipment: wood-fired arch, drop flue pan, continuous flow, arch fan, finishing pan, and steam hood.
The Rusted Flatbed Farm, for its maple syrup operation, utilizes buckets rather than vacuum lines. Likewise, it uses a single-batch flat pan for the evaporator. This set-up is ideal for a maple syrup operation geared toward darker, more robust-flavored maple syrup (which tends to happen with the longer boils on flat-bottomed pans). This is not sustainable for black walnut syrup, which requires vacuum tubing and higher efficiency pans to compensate for the lower sap production and sugar content of black walnut trees. Accordingly, the project requires the acquisition of specific equipment and materials.
After the tapping season, a grad student with an appropriate skill set will be retained to help create graphs and charts and analyze trends in the data. An article will be created with sections on research findings, best practices learned, and an analysis of the costs, labor, and potential ROI for the black walnut syrup operation.
The article will be presented at an open house at the Rusted Flatbed Farm in the fall of 2024. The event will include a tour of the facility, tastings during lunch, and afterwards a discussion of the findings of the report. The invitees will be drawn through outreach, and particularly among the members of the Indiana Maple Syrup Association (IMSA) and the Indiana Nut and Fruit Growers Association (INFGA). A survey among the attendees will assess the flavor, degree of interest in purchasing, producing, or selling (per size of bottle, and blend), and feedback regarding the report and its conclusions.
The final report will include an updated article, summary of the open house, and survey results. The final report will be submitted for posting on the websites and newsletters of IMSA, INFGA, and their national organizations.
Research
The 2024 Season
Black Walnut on Buckets
The Farm placed bucket taps on 23 black walnut trees and 18 maple trees (5/16" poly taps leading down to food-grade buckets). Based on suggestions of other black walnut tappers, the taps were drilled through the thick ridges of the bark. Some prior studies had suggested that the softer wood of black walnuts resulted in tap failures (coming loose), and that the ridges would help support the taps. The tapholes were also conservatively drilled, around 1 3/4 inches. The Farm also only placed one tap on each tree, even if the size of the tree could accommodate more taps.
Black Walnut on Vacuum Tubing
The Farm ran 51 taps on 5/16" tubing, using 7 "Ys" to split the lines to reach different trees. The "lunchbox" style vacuum pump consisted of a diaphragm pump run on pneumatic pressure (an air compressor). This is the most cost efficient and energy efficient vacuum system for a small operation. Originally, the Farm used stainless steel taps, hoping to avoid the waste and expense of disposable poly taps. But with the ridges of the tree bark, it was difficult to use a slide hammer to properly set the tap (it would catch on nearby ridges). Within days it was clear that the vast majority of the taps had lost their seal, and it became clear that the steel taps must be replaced with poly tubing. Rather than re-using the same taphole, a new taphole was drilled for the poly taps. This proved an irreversible mistake. The porous nature of the black walnut tree caused the air to be drawn in from the old taphole, resulting in a near complete loss of vacuum pressure. Sap would also bleed from the original taphole.
For boiling, the black walnut sap production was never sufficient to boil on the Lapierre evaporator (which requires about 10 gallons of sap for minimum operating level). After using reverse osmosis to concentrate the black walnut sap, the Farm purchased a propane fish fryer, typically boiling about 2-4 gallons of concentrate each run.
The 2025 Season
For the 2025 season, the project was repeated, running parallel vacuum tubing lines with 38 black walnut taps and 56 maple taps running through the same wooded area. The black walnut lines contained no "Ys" and allowed frequent introduction of air at the furthermost tap. The vacuum tubing results are usable and will be incorporated into the final report.
Based on a Southern SARE grant released after this grant began (OS21-143), the Farm learned that gravity vacuum lines may provide as much as 400% more sap as vacuum pressure lines. Instead of repeating the research on buckets, 3/16" gravity lines were run on 32 black walnut taps.
The data from the research is still being compiled for a final report that will be presented at the Field Day.
For the 2024 season, the research project largely failed. This resulted from poor weather and errors in tapping methods. Central Indiana experienced unusually warm temperatures which corresponded with historically low sap production. One of the area's most established sugarbushes, located about forty miles due west in New Castle, Indiana, had sap production at 40% of a typical season. Many other Indiana sugarmakers, particularly those relying on buckets rather than high vacuum tubing, saw similarly disappointing results. The results for projecting sap collection should probably be considered well-below typical expectations.
The 2025 was generally successful, except in regard to the gravity tubing. The gravity tubing lines, as configured did not have sufficient grade to create sufficient pressure. As a result, the sap did not flow and remained trapped in the tubing except during substantial flows. The gravity tubing research is a failure.
As for general results, the maple and walnut flows tended to match each other. It appears the same reactions to temperatures operate in both maples and black walnuts.
The research on buckets is probably compromised due to poor tapping practices. But the walnut sap production is significantly lower. For instance, on a February day when maple taps averaged .7 gallons per tap, the black walnuts only averaged .016 gallons per tap. As for tubing, black walnut remains significantly lower. A common run resulted in 2.1 gallons per tap of maple compared to .26 gallons per tap of black walnut. These have not been adjusted for the size of the tree: overall the maples are larger than the black walnuts.
Due to the volume produced by the maples, much higher levels of pressure were achieved in the maple lines (well over 20" of mercury) in peak flows. The black walnuts generally stayed in the range of 13"-18" of mercury, well below industry standards for high vacuum tubing (which should peak at 28"). For reasons unclear, the high vacuum pressure on the maples during peak flows caused the pressure gauge to break in both 2024 and 2025. A more powerful vacuum system may be needed to achieve optimal pressure in black walnuts.
As for sugar content, the maples consistently ranged between 1.5% and 3%, most often around 2% sugar. The black walnuts ranged between 1% and 2%, and most often around 1.5% sugar.
Educational & Outreach Activities
Participation Summary:
During the past two years, the Rusted Flatbed Farm has been visited by several sugarmakers interested in the walnut operation during the sap season. Additionally, the farm was visited by Cub Scout Pack 8 where they learned the process and then camped out in the sugarbush in February 2025. The Farm has informally discussed its operations with several sugarmakers through the Indiana Maple Syrup Association, including during its events at the Pioneer Village at the Indiana State Fair (August 2024, 2025) and at the association's Annual Meetings (December 2024, 2025). Additionally, the Farm has networked with other sugarmakers in Indiana and beyond.
The Farm provided a black walnut syrup tasting and presentation during the Purdue ACER Grant trip to the maple syrup equipment Vermont Open House Weekend in April of 2024. In attendance were a dozen extension officers and sugarmakers.
Most recently, in March of 2025, the Farm presented at the Purdue Small Farmers Conference, which included a presentation and tasting of both fresh black walnut sap and black walnut syrup. It was attended by two dozen local farmers and extension officers.
In October of 2025, the Farm will host a Field Day to present the complete findings of the research project. Notice of the Field Day and sign-up information will be posted in the July and September newsletters, respectively, of the Indiana Maple Syrup Association and the Indiana Nut and Fruit Growers Association. The Field Day will include lunch, a tasting, and a tour of the grounds and equipment. Attendance will be limited to 50 people.
Learning Outcomes
For tapping, several lessons were learned:
- Stainless steel taps that use slide hammers are incompatible with black walnut tapping due to the ridges of the bark.
- Tapholes should be drilled in the ravines of the bark.
- Tapping through the ridges makes it difficult to estimate how far the taphole extends into the tree.
- The crumbly outer bark of black walnut trees is difficult to clear from the taphole and can easily gum up the taps.
- Even while tapping in the ravines, to ensure access for clean drilling and tap removal, it may be necessary to clear some of the outer bark ridges. I recommend a putty knife.
- Black walnut tapholes should be drilled deeper than maples, 2 1/2 "- 3" to ensure a sufficient cavity for the sap to pool and flow.
- Extra care should be given to ensuring the tapholes are clear of debris. One swift movement is ideal for tapping maples, but additional strokes may be necessary for the softer wood of black walnuts.
- Due to the low sap production, trees with sufficient size must have multiple taps.
For tubing, a few lessons were learned:
- Because black walnut trees have significantly less sap production and a much greater proportion of gas (both maple and black walnut exude a mixture of gas and sap from tapholes), days with low flow cause the sap to become "stuck" in the lines.
- The use of "Ys" should be avoided to increase flow.
- Based on the observations of other black walnut producers, it is advisable to periodically introduce air at the furthermost tap to increase flow. This is only effective if there are not "Ys" or there is a shut-off valve to isolate the introduction of air.
- Based on a Southern SARE grant released after this grant began (OS21-143), gravity vacuum lines may provide as much as 400% more sap as vacuum pressure lines. This may have to do with the gas content of black walnut sap.
For boiling, the black walnut sap production was never sufficient to boil on the Lapierre evaporator (which requires about 10 gallons of sap for minimum operating level). After using reverse osmosis to concentrate the black walnut sap, the Farm purchased a propane fish fryer, typically boiling about 2-4 gallons of concentrate each run.
Project Outcomes
The Farm is in the process of compiling the data for a final report that will be presented at the Field Day in October.
The most critical question is whether gravity tubing is substantially more effective than vacuum tubing for black walnuts. In the season ahead, the Farm intends to run gravity tubing on a row of black walnuts with a sufficient grade.