B. On the way to the packing
shed:
Shade the load to prevent sunburn and overheating. Give the produce
a smooth ride, not bumpy.
C. In the packing shed:
Get the crop into a cooler as quickly as possible (30 minutes to a
few hours). Optimum temperature is the most important factor to
maintain quality.
Pre-cool many of your crops, with either a forced air cooler inside
your walk-in or a dunk tank outside. A continuously flowing cold water
bath conducts heat away. Do not hydro-cool eggplant, garlic, or onion.
75-100 ppm chlorine in the wash water will lower the number of pathogens
(human or plant) floating around, but note that most organic certifiers
allow chlorine only at the same level allowed by the Federal Safe Water
Act for municipal water (4ppm). Check with your certifier about using
hydrogen peroxide instead, in a 0.3-3% concentration. Amount varies with
crop.
D. Packaging:
- Packaging reduces air movement and therefore rate of cooling also,
so there is a trade-off between close packing for higher relative humidity
and too close packing which restricts air circulation.
- No rough surfaces, sharp edges, or nails which could puncture or wound.
- Prevent water loss by covering stacks of produce with tarps, or packing
it into bags of either paper or plastic. Microperforated plastics have
tiny pores to let condensation out.
- Don't underfill boxes and don't overfill, but hold items tight within
the box. Pack to immobilize, cushion, and avoid impacts. Can use paper
wraps, dividers, or cushioning pads.
- The package, not the produce, should bear the stacking load.
E. In the cooler:
Temperature: Keep vegetables just above their freezing point
(32°F), or just above their chilling point for chilling sensitive plants
(41-46°F, mod. sensitive; 55-59°F highly sensitive). Refer to tables (Knotts,
Kader, or Bartsch) for specific recommendations for each vegetable. 40-41°F
is ok for most.
Vegetables which are highly chilling sensitive are eggplant and tomato.
Keep these ~ 70°F and tell customers not to put tomatoes in the fridge.
Some moderately chilling sensitive vegetables are beans, peas, cucumbers,
peppers, summer squash, pumpkins, some melons, and potatoes.
Relative humidity: At a given temp. and rate of air movement, the rate
of water loss depends on relative humidity (RH). Most vegetables want
90-98% except for dry onions and pumpkins (70-75%).
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Be sure to measure relative
humidity, and maintain or add moisture: Put a humidity gauge and a
thermometer in the cooler, away from the door and not under the refrigeration
unit.
- put a vapor barrier on the warm side of the cooler wall and install
good insulation
- regulate air movement and ventilation in relation to the produce load
in the cooler
- wet the floor and sprinkle produce with water
- use waxed boxes
- place a damp cloth on top of produce in the box. This also helps cool
by evaporation.
- use plastic bag liners in containers, or poly films for packaging,
or use a 5% vented liner
- keep the refrigeration coils within ~2°F of air temp
- add crushed ice to crops which are not chilling sensitive and tolerate
water (carrot, sweet corn, cantaloupes, lettuce, spinach, broccoli,
green onions)
Ethylene (C2H4) is a hormone produced by plant metabolism. Some plants
give off a lot (apples, other fruit), and most ripen faster if exposed
to it. Ethylene also enters the environment from combustion engine exhaust
and non-electric heaters. Some ethylene sensitive vegetables are: leafy
greens, carrots, cucumber, legumes, eggplant, watermelon, potato and sweet
potato. Good air circulation helps.
F. Loading the cooler:
Stack boxes with air space between pallets and room walls for good
air circulation.
G. Storage life:
Usually, the lower the storage temp (down to just above their freezing
point) the longer vegetables keep. Refer to Knotts or Kader for tables
on longevity in storage. Best way is to know your own product and check
it yourself. Would you want to buy it and eat it?
H. Individual Crops as Examples:
Lettuce: High surface to volume ratio, high respiration rate.
Wilting is main cause of damage and Vit. C loss. Leafy green, so stay
away from ethylene (decreases shelf life and causes browning).
Tomato: Tender skin, easily damaged. Harvest by pulling up at the
natural stem/stalk break point. Chilling sensitive: below 50°F you see
lack of color development, decreased flavor, increased decay, water soaked
appearance. If dunked in water to wash, then water temp should be warmer
than tomato so that tomato does not take up water and pathogens from the
water.
Carrot: Physical or mechanical damage is main cause of loss. Carrots
sprout under improper storage conditions. Sensitive to ethylene. Carrots
can be top iced.
I. Resource List of Publications and Websites with Vegetable Postharvest
Information
Bob Meyer and Astrid Newenhouse
- Postharvest Technology of Horticultural Crops, Second Edition.
1992. Adel A. Kader. University of California Division of Agriculture
and Natural Resources Publication 3311. Lots of technical and practical
info w/ tables, 33 chapters by different authors.
- Growing Vegetable Crops in Wisconsin, A Guide for Fresh Market
Growers. 1997, 1998 (Series of 5 publications, each ~20 pages on a specific
group of crops). K. A. Delahaut and A.C. Newenhouse. University of Wisconsin
Extension Publication Series A3684-A3688. Practical how-to guides.
- Work Efficiency Tip Sheets. 1999. B. Meyer, A. Newenhouse,
M. Miquelon et al.. Univ. of WI Extension Publication Series A3704.
Packing shed layout, Mesh produce bags, Specialized harvest cart, Narrow
pallet system, etc. Informative fact sheets, see http://bse.wisc.edu/hfhp/VeggyTipSheets.htm
- Small Scale Postharvest Handling Practices. A Manual for Horticultural
Crops, Third Edition. 1995. Lisa Kitinoja and Adel A. Kader. Postharvest
Horticulture Series No. 8, Department of Pomology, University of California
at Davis. Simple sketches of coolers, store rooms, packing lines, handling.
- Produce Handling for Direct Marketing. Roadside Marketing Series.
1992. J. Bartsch, R. Kline. Northeast Regional Agricultural Engineering
Service. NRAES-51. Cooperative Extension, Ithaca, NY. (607) 255-7654.
Practical tips, cooler construction, & specific recommendations by crop.
27 pgs.
- Knotts Handbook for Vegetable Growers, Fourth Edition. 1997.
Donald N. Maynard and George J. Hochmuth. Wiley. All kinds of lists
and tables such as cooling requirements for specific crops, depth of
rooting, nutrient absorption, sprinkler nozzle output, pesticide rates.
Library reference.
- Postharvest: An Introduction to the Physiology & Handling of Fruit,
Vegetables, & Ornamentals, Fourth Edition. 1998. Ron Wills, Barry
McGlasson, Doug Graham, and Daryl Joyce. CAB International Press. Research
and technical info textbook.
- Sustainable Vegetable Production from Start-Up to Market. 1999.
Vern Grubinger. A comprehensive overview of small farm production including
postharvest handing.
- http://www.bae.ncsu.edu/programs/extension/publicat/postharv/
North Carolina's post harvest handling website. Check out the Post Harvest
Technology Series, worth the trip! USDA packing standards listed.
- http://www.cals.ncsu.edu/sustainable/peet/index.html
North Carolina's sustainable agriculture production ag series. Production
information is all text.
- http://www.ams.usda.gov/
USDA's Alternative Marketing Service website. Has links to direct marketing,
farmer resources, & CSA's.
- http://www.attra.org/
http://attra.ncat.org/attra-pub/postharvest.html
ATTRA's site (Appropriate Technology Transfer for Rural Areas), and
post harvest handling site. Good general information for growers. There
are also some production guides.
- http://osu.orst.edu/Dept/NWREC/vegindex.html
Oregon State University's production guides. Short and sweet, basic
info on each crop.
- http://www.sfc.ucdavis.edu/cgi-win/spec_crop.exe/
UC-Davis Small Farm Centers website and specialty crop index.
- http://bse.wisc.edu/hfhp/
Healthy Farmers, Healthy Profits Project for small scale growers.
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This material was developed by the Healthy Farmers, Healthy Profits
Project, whose goal is to find and share work efficiency tips that maintain
farmers' health and safety and also increase profits.
For more information, call (608) 252-1054 or visit our website at http://bse.wisc.
edu/hfhp/
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