Characterizing Chestnut 'Cure' as a Function of Time, Temp & RH, Based on Nut Size, Color and Shape

Progress report for FS23-355

Project Type: Farmer/Rancher
Funds awarded in 2023: $15,000.00
Projected End Date: 03/31/2025
Grant Recipient: Mountain Grown Chest
Region: Southern
State: North Carolina
Principal Investigator:
Dr. Ron Fritz
Mountain Grown Chest
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Project Information


The solution:

To inexpensively solve the difficulty of determining when chestnuts are ready for consumption (by visual or tactile inspection, particularly for those kept at low temperatures and high humidity to maximize shelf life), this solution is to develop guidelines via statistically designed experimentation, the results of which can reasonably forecast curing rates under various temperature/RH circumstances.  So given knowledge of the thermal and RH history of the nuts, one can then prescribe the time required at a certain temperature/RH combination to accelerate, delay or maintain cure to bring nuts to optimal sweetness at the intended time of consumption/use.

With this grant I will be funding a partnership with North Carolina State University Kannapolis Laboratory to carry out this designed experiment (described in the 'Approaches and Methods' section of this submission).  This study and its results will then be peer review published (open access) in a suitable journal for use by academia, industry and consumers with the aim of educating and arming them so that more of what the chestnut has to offer can be obtained.


Project Objectives:

Chestnuts will be supplied by Mountain Grown Chestnuts, LLC, Burnsville NC 28714, from the 2024 harvest.  They will be kept at 32 F and 90% humidity until pulled from the cooler for 72 F/60% RH curing.

The study will be comprised of a 2^5-1 fractional factorial, fully replicated (n=2) designed experiment.  Factors and levels will be as shown below.  The primary response will be '% soluble solids' (brix content) and will be determined via best practice 'wet chemistry' (WC) methodologies, done for each of the 32 treatment combinations (with '0.15' lbs. of nuts/treatment combination):

Harvest Date Day 4 Day 24
Nut Size Small (< 0.75" diam.) Large (> 1.25 diam.)
Nut Color Light Dark
Nut Shape 1 Flat Side (End Nut) 2 Flat Sides (Middle Nut)
Days Cold Stored (32F, 90% RH) 0 days 14 days

The above full factorial experiment will be conducted at four different dwell times as shown below (with all dwells at 72 F and 60% RH):

  • 0 hrs. dwell at 72F/60% RH
  • 48 hrs. dwell at 72F/60% RH
  • 96 hrs. dwell at 72F/60% RH
  • 144 hrs. dwell at 72F/60% RH

Statistical linear models for each of these 4 dwells will be created, from which curing curves will be developed for combinations of the statistically significant factors found.


Materials and methods:

Chestnuts will be harvested twice daily, 7 days/week during harvest (late September thru October).  The intent is for chestnuts to be gathered at harvest as close as possible to when they naturally fall from trees.  Harvested chestnuts will then be  inspected (standard inspection to ensure they are marketable nuts), washed (with cold water) and immediately refrigerated at 32F, 90% RH.  This will be done twice daily immediately after their harvesting from the orchard (so to minimize time from falling from trees to being refrigerated).  

Then each Monday, for four consecutive Mondays, four select treatment combinations (n=8 for each, so 32 separate samples) will be assembled at the orchard (as per the experimental matrix - see attachment) and then 'immediately' (asap as distance is 3 hours drive) cold delivered to NC State's Kannapolis laboratory for analyses (Brix and Moisture done via NIR Spectrometry to build a first ever NIR model for this on the Dunstan variety in North America, then Brix and Moisture done via best practice wet chemistry methods).   On the day of receipt of nuts, the Lab will analyze two replicates of each of the four treatment combinations and repeat this at 48, 96 & 168 hours later with the balance of the samples, with these combinations being stored at 72F, 60% RH.

The above is then repeated each week for the remaining 12 treatment combinations.

Experimental Design (as of 2-29-24)

Research results and discussion:

Due to a late frost May of last year, which greatly diminished the harvest, we were unable to conduct the experiment as planned (on the 2023 harvest). Consequently, the study will be conducted on the 2024 harvest. If a late frost occurs this Spring, we will be requesting an extension to push the study back another year.

Participation Summary
1 Farmers participating in research

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

This research will be published in its entirety in a peer-reviewed journal.  As an educator and trainer my entire career, I am also very open to online training, webinars, and other training ideas others may have.

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.