Final 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.
This project aimed to advance black walnut (Juglans nigra) syrup production by testing sustainable tapping practices and collecting performance data through parallel maple and black walnut tapping operations. By running parallel operations on the same sugarbush, the timing and production of the maple and black walnut can be compared. This offers insight into the degree that black walnut should use maple tapping practices.
The project contemplated tapping with both buckets and vacuum tubing. With buckets, data can be analyzed at each tree. With vacuum tubing, higher yields can be drawn. Black walnuts produce substantially less sap than maples, and increasing sap production is one of the biggest challenges for black walnut syrup producers.
Sap was collected and measured daily during each run. A digital refractometer was used to measure sugar content. A graduate student from Purdue University, Jean Fritz Saint Preux, analyzed the data and created a report with charts and calculations included below. Another report with pictures and descriptions of the tapping process was also created. Additionally, a best practices guide and business plan for a small operation was compiled.
The findings of the research were presented at a Field Day at the Rusted Flatbed Farm, which include a presentation of results, the best practices guide and business plan, a tour of the sugarbush, a black walnut syrup tasting, and large and small group discussions.
The major research conclusion is that most maple guidelines should also apply to black walnuts as the timing of trunk pressure and sap flows in relation to changes in temperature are quite similar. It was also learned that stainless steel taps should not be used on black walnuts. Poly taps work well, and the tapholes should be drilled between the ridges of the black walnut bark and not through them. Because sugar content seems to diminish over the course of the season, which is dissimilar to maples, black walnuts should be tapped earlier in the season.
These lessons learned have been put into practice and shared with other black walnut producers. Based on observations between the maple and black walnut on 5/16" tubing, the next season will incorporate 3/16" tubing on the black walnut lines in hopes of achieving a higher level of vacuum through a natural grade gravity effect.
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.
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.
Results
Jean Fritz Saint Preux, a grad student at Purdue University with experience in maple research, was retained to create a report on the results. A summary of the project and its results has also been created. These two reports are embedded below.
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.
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.
The Field Day was held on November 8, 2025. It was circulated on Facebook through the Indiana Maple Syrup Association, The Black Walnut Syrup Makers page, and the Indiana Nut and Fruit Growers Association. Attendance was limited to 50 people and the event was at capacity very quickly. About 30 people were turned away.
On the Field Day, there were a few no-shows resulting in 40 attendees representing 31 farmer/rancher operations. The attendees came from Indiana, Kentucky, and Ohio. At sign-in, 16 stated they were interested in tapping black walnuts as a hobby, 6 were interested in a small operation, 5 were interested from a homestead/survivalist perspective, and 4 were curious. Most of the attendees had tapped maple syrup before, and a few had tapped black walnut.
The presentation of the results of the study included hand-outs with best practices and a business plan/budget for a small operation. This guide is available in the link in the Information Products section below under "Black Walnut Syrup Operation."
The presentation was followed by a black walnut tasting. The attendees were asked to describe the flavors and reactions to the tasting.
| Tasting Comments | |
| Identified Flavors | |
| caramel | 6 |
| butterscotch | 5 |
| toffee | 5 |
| buttery | 5 |
| nutty; roasted nuts | 5 |
| smoky | 2 |
| burnt cotton candy | 1 |
| woody | 1 |
| vanilla | 1 |
| light molasses | 1 |
| sorghum-like | 1 |
| maple syrup candy | 1 |
| hint of blueberry | 1 |
| slight bitterness | 1 |
| Aroma | |
| smoky | 4 |
| caramel | 1 |
| sweet sourdough | 1 |
| lighter than maple | 1 |
| no lingering nose | 1 |
| Attributes | |
| smooth | 2 |
| rich; deep rich tang | 2 |
| warm | 1 |
| mild | 1 |
| lingers on the tongue | 1 |
| Other Comments | |
| sweet | 6 |
| sweet but not overwhelming | 1 |
| not as sweet | 2 |
| has aftertaste | 3 |
| no aftertaste | 2 |
| deeper flavor than maple | 1 |
| not as overpowering as maple | 1 |
| comparable to golden grade maple | 1 |
| better than maple | 4 |
| not better than maple but so distinct you want more | 1 |
| light; lighter than maple | 2 |
| very good; really like it | 3 |
This confirms the unique flavor of black walnut syrup, and most often described as butterscotch.
There were many good discussions throughout the presentation, tasting, lunch, and tours of the farm.
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 Field Day was held on November 8, 2025. The notice was circulated on Facebook through the Indiana Maple Syrup Association, The Black Walnut Syrup Makers page, and the Indiana Nut and Fruit Growers Association.
The president of the Nut and Fruit Growers reported that the post went viral:
"It has over 51,000 organic views, 124 shares, and well over 400 like/love interactions with no sign of it slowing down. I don't think we've had a post go viral in the INFGA group like this before."
Many of the commenters expressed that they had never heard of black walnut syrup and were excited to taste it or try to make it.
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.