After starting from seven to 10 days earlier than usual in the last week or so of July, this year’s almond harvest was picking up steam by the first of August. However, getting the crop on the ground isn’t the same as getting full value for the nuts once they’re delivered to the processor. That requires managing moisture levels of the nuts properly while they remain in the field.
“Delivering a quality crop to the huller requires attention to detail in many areas including field drying, stockpile layout and materials used for tarping stockpiles,” says Franz Niederholzer, University of California Cooperative Extension farm advisor for Sutter and Yuba Counties.
As he points out, wet nuts can reduce the quality and market value of your crop in several ways. Stockpiling high-moisture nuts can cause nuts to mold. Also, it can cause them to heat up, result in concealed damage. Processors handle nuts suspected of being wet or exposed to heat separately. If concealed damage is found, you can suffer a significant discount on the price you receive compared to high quality nuts.
Wet nuts run through the huller also are at a higher risk for chipped kernels, embedded shell and foreign material off-grades – all of which also reduce their market value and the price you receive.
Niederholzer offers some tips for picking up and stockpiling nuts to minimize moisture problems. They’re based on research by UCCE specialist Bruce Lampinen and plant pathologist Themis Michailides. Some, Niederholzer points out, are no-brainers. Others aren’t so obvious:
Don’t deliver wet nuts.
When deciding if nuts are ready for windrowing or pick up, keep in mind that nuts under the tree or deeper in the windrow will be wetter than those in the tree rows or near the top of the windrow.
“Nuts on the orchard floor closer to the trunk and in the most shaded areas have as much as 2 percent higher moisture than nuts out in the tractor aisle where there is maximum sun and heat,” Niederholzer says. "A similar swing in nut moisture was measured from the top to the bottom of windrows. If you base the timing of nut windrowing and/or pick up by checking just in the driest location on the orchard floor or in the windrow, you may start too early.”
For stockpiling nuts, he recommends aiming for a target of 11-percent to 12-percent hull moisture and 4-percent to 5-percent kernel moisture. However, a kernel moisture reading of less than 6 percent is acceptable, Niederholzer notes.
Experienced growers/hullers can tell when almond nuts are ready for pick up based on handling the nuts. “If the hulls or kernels just fold over and break, they are too wet to stockpile,” Niederholzer says. “You can also use moisture meters to test the nuts and hulls for moisture.”
Water activity - a measure of the free water available for physical or chemical reaction - predicts the risk for microbial contamination more accurately than commercial equipment that measures moisture content, Niederholzer adds. However, there is a good relationship between almond nut moisture content and water activity.
More information on post-shaking moisture management and water activity is available on Almond Board of California's web site (http://www.almondboard.com/Growers/Documents/Harvesting%20Clean%20and%20Safe.pdf).
Consider conditioning the nuts.
This may be particularly worthwhile in areas of an orchard where mites, disease or water stress produced significant leaf loss at shaking.
“Blow out the trash and move the nuts out into the more sunlit portion of the orchard floor in the tractor aisle,” Niederholzer says. “Conditioning helps dry nuts that have been rained on while scattered on the ground after shaking or lying in windrows. In addition, some growers are moving to conditioning nuts almost immediately after harvest. This speeds drying and helps get the nuts out of the orchard and water back on the trees as soon as possible.”
Think North–South, not East–West.
He advises building your stockpiles on a north-south alignment, not east-west. This reduces shading and overall condensation in the stockpile.
Place black on white tarps with white side up.
When covering stockpiles, use white-on-black tarps with the white side facing up. This keeps temperatures and condensation under the tarp down, Niederholzer notes. Clear tarp materials produced the largest day-to-night temperature swings and the most mold growth under the tarps compared to white or white-on-black tarp materials in UC studies.
Plan for the long range.
Prune the trees so that no more than 20 percent of the orchard floor is shadowed by the foliage. “This provides a balance between light capture for crop production and drying power on the orchard floor, Niederholzer explains. “ Also, wherever possible, plant an orchard with rows oriented north-south. This distributes light energy evenly on each side of the tree, so nuts can dry more uniformly.”