By Annalisa Hultberg, Extension
Educator, Food Safety
Harvest is well under way, and crops
are coming in strong in many areas with our intense heat. As you prepare your
products for sale, many are rinsed to remove soil or cooled in water to crisp
them up. While rinsing produce can cool it and remove that soil, it also can
spread contamination that might be present on the exterior to other produce,
making a small problem a bigger one.
For example if a melon or lettuce
leaf had fecal contamination from a bird or rabbit, and that produce was put
into a bulk washing tank, the pathogens in the feces can spread to the other pieces via the water.
Contamination can also be introduced from workers hands or from dirty wash
tanks or tools. Illness from the bacteria can include diarrhea, vomiting,
fever, nausea, and can even be more serious for some individuals with
compromised immune systems.
Some basic steps can go a long
way to reduce the potential risks of contamination in your postharvest washing,
and also have the added benefit of improving shelf life and storage quality of
your product. Here are some tips to think about as you rinse your fresh
produce to ready it for sale.
1. All water used for washing,
cooling and other postharvest use must be like drinking water.
First, consider the quality of the
water you are using to wash your produce. Well (ground) water should be
tested at least annually for bacteria. Municipal water does not need to be
tested. Surface water like streams and ponds should never be used for
postharvest applications like washing produce, since the water quality is
highly variable and this water is vulnerable to bacteria and pollutants from
animals, runoff, flooding and other sources of contamination.
Test well
water at least annually for presence of generic E. coli. Results
should indicate not detectable in 100 ml. When you call the lab, they
might say that a potability or drinking water test is generally for total
coliforms. Coliforms are an indicator of the water quality and of
bacterial contamination in the well, but E.coli is better as
it is a direct indicator of fecal contamination, and therefore the likelihood
that there will be harmful pathogens in the water. The FSMA Produce Safety Rule
requires testing for the presence of generic E. coli. Tests
are about $35- $40 each.
To find a lab: Minnesota Department of Health Accredited Labs database or
for more information about water testing and to find a lab, see Testing Water for FSMA Produce Safety Rule.
Taking a
water sample from a well head
2. Don't wash unless needed
Not all produce should be washed
before it goes to the customer. Herbs and berries are typically not washed
until right before consumption, as washing begins the process of degradation
and will result in lower quality produce with a shorter shelf life. Of course
many crops do need to be washed to remove field soil and/or to hydrocool and
crisp up. However sometimes washing can actually increase the risk of
contamination, as water spread pathogens readily, moving fecal contamination
around via the water. So, washing should be done with care and only when
needed.
Consider the crop before washing. Do
the peppers, cabbage, tomatoes or eggplant need to be washed? Depending on the
crop, how it was grown (on plastic much for example, or in a high tunnel), on
the rainfall, perhaps no postharvest cleaning is needed at all. Sometimes they
are simply dusty and a light rub with a clean towel or paper towel is all that
is needed.
All produce should be washed before
consumption by the consumer. You can remind your customers that your products
have been "farm washed", but they will need to rinse all produce
again in clean water before consumption.
3. Change water as necessary to
maintain sanitary conditions
Change wash water often! When it
looks dirty, between crops, or another metric you design. Water should not be
allowed to get visibly dirty for long periods of time. Turbidity (the
cloudiness of water from organic material) affects any sanitizer you might use
in the water and can leave your crops dirty and potentially contaminated. You
can use a turbidity tube, Secchi disk or other device to quantitatively monitor
your postharvest wash water. This can make it easier to communicate to workers
when they should change the water because you have a objective
measurement. See this post from MSU about turbidity tubes
and other ways to monitor postharvest water quality.
Turbidity
tube used to measure and monitor postharvest wash water cloudiness
4. Clean and sanitize water contact
surfaces
Tanks should be cleaned and
sanitized regularly. Often, this means each day before or after use. You should
at least rinse out the tank and allow to dry after each use. Occasionally
(perhaps once a week while in use) do a more thorough clean to remove biofilms
that will accumulate. Using a brush, scrub the inside surfaces with a
scrub brush with a detergent like Dawn, rinse and then spray with a sanitizer
and air dry. You can use a sanitizer like a bleach solution, or a product
like SaniDate® 5.0, which is OMRI approved for sanitizing food contact surfaces
and produce wash water.
Read more about cleaning and sanitizing steps and materials here.
Where are tanks stored? It is best to
keep tanks in a building that is sealed to keep animals off them. If that is not
possible, you will need to wash and sanitize before each use in case animals
contaminated the surfaces overnight.
5. Use wash water sanitizer if
possible
The use of a sanitizer in wash water
can increase product shelf life and minimize the potential for pathogens to spread in your wash water. Sanitizers do not
wash produce, but they reduce the overall bacterial load in the wash water and
therefore reduce the potential for cross contamination in the water. If one
leaf of lettuce is in your wash tank has fecal contamination, the sanitizer
will reduce the potential that the bacteria to spread to all the
other leaves via the water.
SaniDate® 5.0 is a good option and
is OMRI approved and used by many farms. Sanitizers are not required but are
recommended, and many farms report that the shelf life of product like greens
are significantly longer when they use a wash water sanitizer. Some examples of
commonly used PAA and hydrogen peroxide sanitizers include SaniDate® 5.0,
StorOx® 2.0, and Tsunami® 100.
Sanitizers
approved for use in produce wash water
6. Use spray tables when
possible
Spray tables are useful for some
items like root crops that can handle a higher pressure spray. Spray tables reduce the potential for contamination of product as the
water is "single pass" instead of recirculated. They can also
be useful for drying crops before storage. You can build a simple spray table
with hard plastic or mesh topping a wooden frame.
Spray table
7. Tips for safe and effective wash
water set ups
Washing configurations do not need
to be fancy or expensive. Hard plastic tanks and surfaces work very well, and
stainless steel tanks and sinks can often be found at restaurant auctions. Wood
is not ideal as a food contact surface it is not easily cleaned or sanitized. Try to avoid flimsy
totes that are not intended for food - they will buckle under the water, and
are also more difficult to clean and sanitize, as they have more nooks and
uneven surfaces.
Hydrocooling
broccoli in the shade of a packing area
Final tips:
It is best to have shade over your
washing area to keep the produce cool (not a tree, which can be a roosting
place for birds).
Where will the water go? Try to keep
it from pooling where it is dumped to minimize mud and standing water which can
attract bugs and animals. If you are washing in a packing area, the water
should go in the drain. If you are on grass, do your best to ensure good
drainage to avoid mud and standing water.
Finally, think about the water
distribution line to get the water from the well to your washing tank. Is the
hose off the ground? It is best to try to dry the hose occasionally so that
biofilms can dry out.
And of course, before you start
washing your produce, wash your hands well. (Whatever is on your hands could
spread to all the produce in the tank, given how water carries pathogens and
other contamination very well.). Wash your hands well for 20 seconds with
running water and soap before starting the washing process. See instructions
on building a low-cost handwashing stand here.
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Thinking about these basic considerations
will yield safer, high-quality produce with a longer shelf life.
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