Tapping New Forest Farming Opportunities in Central Appalachia Through Black Walnut Syrup Production

Progress report for OS21-143

Project Type: On-Farm Research
Funds awarded in 2021: $19,546.00
Projected End Date: 03/31/2024
Grant Recipient: Virginia Tech
Region: Southern
State: Virginia
Principal Investigator:
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Project Information


The proposed solution comes through answers to two studies: quantitative research into the delivery of vacuum through tubing systems to tapped black walnut trees, and qualitative evaluation of the characteristics of walnut syrup. The proposed research will be conducted on Tonoloway Farm in Highland County Virginia.

To address the questions surrounding vacuum on sap harvest, the proposed research will take vacuum measurements along the length of three tubing systems: 3/16” gravity vacuum, 3/16” mechanical vacuum 5/16” mechanical vacuum (5/16” tubing does not work with gravity vacuum because the larger diameter does not allow capillary sap flow). Knowing the actual level of vacuum delivered to the tap will remove one of the major questions about sap flow in black walnut trees: how to get the most sap from each tap. Following the methodology detailed below, data will provide evidence to inform recommendations on types of tubing systems, the maximum length of lines, and cost-benefit ratio of mechanical versus natural vacuum systems. These findings would help to provide guidance for development of new walnut syrup businesses, including the most cost-effective systems. With this information, new farms and forest landowners can enter the walnut syrup market using existing technology without the risk of costly trial and error.

The qualitative side of the proposed research will provide answers about the flavor profiles of walnut syrup. The maple syrup industry grades products based on color and depth of flavor: golden delicate, amber full-flavor, and dark robust flavor. These are generally correlated with the period in the season when sap was harvested, with early sap producing the lightest mild tasting syrup, and later sap runs producing darker syrup with more intense flavors. It has been observed that walnut syrup also varies in flavor and color, but correlations are not well-established. What is needed is a system to grade the quality of walnut syrup. Farmers and landowners would benefit through guidance on controlling variables to  determine specific flavors of walnut syrup. Quality standards also contribute to consumer awareness and marketability of this new product. 

As one of the largest black walnut syrup producers, Tonoloway Farm is able to produce batches of walnut syrup throughout the season with consistent processing methods. Qualitative analysis by expert members of the advisory board will evaluate syrup from specific batches from two seasons and multiple farms. In addition, off-flavors produced by bacteria (if present) or harvesting too late in the season can also be analyzed and defined to inform standards for walnut syrup production.

Project Objectives:

Proposed research on walnut syrup production will focus on two core areas: 1) sap harvesting methods and 2) qualitative characteristics of walnut syrup (i.e., expert panel to evaluate flavors and grades).

1) Sap harvest with vacuum tubing

In recent decades, the maple syrup industry shifted from drip harvest methods to vacuum tubing systems. Numerous studies demonstrated that maple trees respond to negative pressure at the tap hole with increased sap flow (van den Berg 2012). It’s worth noting that current tapping standards maximize sap flow without detriment to the trees themselves. In early 2020, Tonoloway Farm contributed to research showing preliminarily that black walnut trees respond favorably to vacuum too (Rechlin 2020). However, there are two methods of vacuum used in the maple industry: gravity pulling on capillary action through 3/16” tubing, and mechanical vacuum through either 3/16” or 5/16” tubing. While capillary vacuum works well with maple, walnut trees release more gas into the sap lines, which reduces the transmission of vacuum through the line. It remains unclear if high levels of vacuum can be transmitted with walnut sap all the way up 3/16” and 5/16” tubing. 

The proposed research would perform a controlled study on sap flow in the three combinations of tubing diameter and vacuum source. Quantitative data would show vacuum measurements for multiple points along the length of the sap lines. Vacuum gauges will be installed at every other tap along the length of two 3/16” lines with gravity vacuum, two 3/16” lines with mechanical vacuum, and two 5/16” lines with approximately 20 taps each, for a total of 120 data points. This data can be charted against elevation (for gravity vacuum) and distance from the vacuum source (gravity and mechanical vacuum) to determine which method results in the best transmission to vacuum at the tap. The same data would be collected throughout the season at times of low, medium and high sap flow. 

2) Qualitative characteristics of walnut syrup

To evaluate the qualitative characteristics of walnut syrup, samples will be retained from each batch produced at Tonoloway Farm during the 2021 and 2022 seasons. A minimum of three samples per season (early, mid, late) will be taken, with potential for 5-6 samples if conditions allow. They will be labeled by date and charted according to that year’s harvest calendar: early, mid and late harvests.  Samples will be finished to 66-68 degrees brix (measurement of sugar content) and bottled for storage according to industry standards (180-190 degrees F) to ensure stability in storage. Notes will be recorded for any notable circumstances during the production of each batch. In addition, finished syrup samples will be purchased from other walnut syrup producers, to be compared with those from Tonoloway. 

Following the 2022 harvest season, an advisory board will be invited to meet and ascribe qualitative characteristics to each sample. The advisory board will include two persons with a scientific background in tree syrup research, a maple industry professional, and two culinary professionals, in addition to the principal investigator and collaborating farmer. Potential characteristics include visual properties, acidity, flavor profiles, intensity of flavor, and presence of any off-flavors. These characteristics will be correlated to the harvest period from the two sample seasons, and compared with syrup samples taken from other farms. This qualitative data will be used to determine if walnut syrup properties vary according to the period of harvest, while also revealing if there is a point in the late-season after which flavor deteriorates. The advisory board will aim to correlate potential off-flavors with processing notes to determine their origin, if present. Such observations will help producers evaluate their own syrup and avoid practices that lead to off-flavors.

N.B. In the event that COVID-19 prevents the gathering of the advisory board in person, samples will be mailed to each member of the board, along with clear instructions and a survey sheet to collect qualitative data detailed above.


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  • Christopher P. Herby - Producer


Materials and methods:

Much of the time leading up to tapping and syrup collection was spent purchasing and installing the equipment needed for the research, and laying out the initial black walnut sap collection (tapping).  Most of the material acquisition is complete.

The timing and duration of the tapping season is weather dependent and may change slightly from year to year.  This year tapping started in late February and lasted most of March.

During the first year, labor for research line set up, tapping and sap collection and processing is has been slightly less than planned, as setup and data collection didn't take as much time as anticipated. Remaining activities this season include cleaning the research lines, conducting the site survey, compiling data and analysis, and reporting on our findings. 

Data collection is complete for the quantitative part of the vacuum study. We collected vacuum data on 4 different days during the 2022 black walnut sap flow season (during March), on 6 different lines in 3 configurations as detailed in the research plan.

Early in the second year we will have all the trees in the study surveyed (i.e., to determine location and altitude).  We hope to schedule this in late Spring as weather and ground conditions permit.  With this data we can plot results against tubing length and elevation, rather than just tap 1, tap 2, tap 3, etc.

For the qualitative black walnut syrup flavor study, we have multiple samples gathered from the research site (Tonoloway Farm) for the 2021 and 2022 seasons, representing quite a variety of syrup color and flavor profiles. We have also requested black walnut syrup samples from other sites throughout the black walnut growing range in the US to be delivered.

Prior to convening the panel of experts, we are obtaining samples for the black walnut syrup flavor study.  Those should be delivered during April.  We will schedule the expert panel to taste and analyze these samples - tentatively during May 2022.

Research results and discussion:

Initial review of the data gives some very interesting and surprising insights on how vacuum impacts walnut sap flow.  Analysis will be conducted after the syrup season and cleanup are complete in April.  Other results from vacuum study, and the taste panel, will be reported on in the second year.

Participation Summary
1 Farmers participating in research

Educational & Outreach Activities

3 Consultations
2 On-farm demonstrations
2 Published press articles, newsletters
4 Tours
1 Webinars / talks / presentations
4 Workshop field days

Participation Summary:

5 Farmers participated
5 Ag professionals participated
Education/outreach description:

Outreach efforts will include a variety of activities. Initial outreach activities will focus on documenting the on-farm research activities in a form that is appropriate for farmers and landowners, agriculture service providers, and other stakeholders. In Year 1, these activities will include stand-alone educational materials including signage, and take-home or downloadable handouts.  Also in Year 1, the research site will host farm tours for small groups by appointment. Working with our collaborators (i.e., Appalachia Beginning Forest Farmers Coalition, Virginia Tech Cooperative Extension Service) and through our network and web sites, we will target experienced and potential forest farmers who may wish to tap black walnut, agriculture service providers, and potential buyers or processors of syrup products. In Year 2 of the project, outreach activities will include a field day, a presentation at the Southern Syrup Research Symposium, and drafting a review of the research and its applications for posting on digital platforms (i.e., Black Walnut Producers Facebook group).  We will also target larger and more diverse groups including the general public by providing research information at agritourism events such as the Highland County Maple Festival. 

Findings will be disseminated through web-based distribution as appropriate through email blasts, and social media.  Digital outreach for reporting results will use multiple online platforms such as the Virginia Tree Syrup Producers Association website and Facebook page. The team will also produce a peer reviewed journal article and other technical papers. Technical articles may be promoted through maple syrup industry publications (i.e. MapleNews.com).

An education plan will be developed for a field day that will focus on black walnut syrup production. The field day will include visits to the tapped walnut stand and the processing facility at Tonoloway Farm. Presentations of research will take place in the farm’s multi-use building.  It will aim to give people enough information to start tapping black walnut trees and producing syrup. The first part of the field will discuss the differences between black walnut trees and maple trees, highlighting why a farmer cannot tap a black walnut in the same way a maple tree is tapped. Demonstrating tapping, and discussing tapping system set up, tap size, tapping depth, and timing of tapping will follow. The final portion of the workshop will cover the ongoing research and questions lingering in black walnut production. As a new industry, the process of making walnut syrup has yet to be perfected, further justifying the proposed experimentation.

 Acknowledgement of the challenges of conducting this project in the era of COVID:

The actual research will be conducted outdoors, and alone by the project cooperator at Tonoloway Farm.  However, for all planned activities, the project will take proper precautions and will follow all VA Department of Health COVID and CDC recommendations and guidelines. We will also follow procedures set by Virginia Tech and our collaborators. For instance, in response to the COVID reality, this year the project team has experience in providing safe learning experiences through organizing and presenting online tree syrup workshops, webinars, and certificate classes.  Even with these new formats, the workshops have provided benefits across the region as participants have come from several states.

Because there aren't guidelines specific to farm visits, it is suggested that agritourism sites follow the guidance for farmers' markets. We will follow these recommendations and modify our procedures as the situation changes. For instance recommendations include only receiving one group of visitors of no more than 10 persons at a time, and these visits are conducted entirely outdoors. Physical spacing of 6 feet is maintained between farmers/presenters and visitors, and masks are worn at all times. Discussions will take place outdoors or in an open-air space. Signage about health public health reminders will be posted, and will be communicated with visitors prior to their arrival. Although sampling is discouraged, sampling products is important to this project. As needed we will provide samples in a modified format - small individual containers that will be disposed of after use, available hand sanitizer and hand washing and other recommendations according to CDC guidelines will be followed.  Should on-farm in-person sampling not be possible, we will arrange to send samples with questionnaires by mail to the advisory board members.

Project Outcomes

1 Grant received that built upon this project
6 New working collaborations
Project outcomes:

This farm is becoming a role model for others that might produce black walnut syrup.

Information Products

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.