- Additional Plants: trees
- Miscellaneous: syrup
- Crop Production: forest farming, forestry
- Farm Business Management: new enterprise development, value added
- Sustainable Communities: local and regional food systems
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 from proposal:
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.