California Strawberry Commission
MAINTAINING
QUALITY
OF FRESH
STRAWBERRIES
PO Box 269
Watsonville, CA 95077
831.724.1301 phone
831.724.5973 fax
[email protected]
www.calstrawberry.com
© 2011 California Strawberry Commission
Table of Contents
Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Process Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Harvest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Transport to Cooler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Staging for Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Forced-Air Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Modified Atmosphere Pallet Bag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Storage at Cooler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Staging for Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Preparing Refrigerated Trailer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Loading the Refrigerated Trailer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Unloading at Distribution Center (DC) / Holding on Dock at DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Storage at DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Staging for Loading at DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Transport to Store . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Unloading at Store/ Holding on Dock at Store . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Storage in Walk-In Cooler at Store . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Stocking and Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Additional Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
BEST HANDLING PRACTICES FOR STRAWBERRIES
1
CALIFORNIA STRAWBERRY COMMISSION
California Strawberry Commission
Best Handling Practices for Fresh Strawberries
Background
Strawberries are among the most perishable produce items. They are harvested at a point where they are ready to be
consumed unlike many other fruits that are harvested at a less sensitive unripened stage and then ripened later.
Strawberries have a relatively high rate of respiration and are highly susceptible to water loss and mechanical
damage. They are also susceptible to decay from fungus — principally Botrytis Rot and Rhizopus Rot. This all means
that strawberries require special attention to all aspects of postharvest handling, especially cold chain management.
Maintaining strawberry temperature as close as possible to the optimum temperature range of 32°F to 34°F will
maximize strawberry quality and shelf life in several ways including:
• Slowing the growth of plant pathogens (Botrytis; Rhizopus, etc.)
• Reducing the respiration rate
• Minimizing water loss
Days of Quality Shelf Life
The graph below shows the relationship between storage temperature and shelf life. Note that this shelf life
information is provided as a general reference — the actual shelf life of strawberries will be affected by many factors
such as variety, growing location, season, preharvest practices, preharvest weather conditions, etc.
20
15
y=190.5e-0.0742x
10
5
0
32
42
52
62
72
Degrees (F)
Strawberry Shelf Life Curve
While the principle of maintaining proper temperature for strawberries may seem simple and obvious, there are
many steps in the distribution of strawberries and the practice of maintaining proper temperature control to ensure
maximum quality and shelf life. Therefore, detailed attention at each step of distribution is required. This document
outlines each of the major handling steps of distributing strawberries, the common problems in each of those steps
and recommended best practices to ensure proper temperature management to deliver the freshest product
possible to your customers.
BEST HANDLING PRACTICES FOR STRAWBERRIES
2
Process Map
Accumulation
in field
Harvest
Forced air
cooling
Staging/set up
on tunnel
Transport
to cooler
MA
required?
Yes
Staging
at cooler
(outside)
MA pallet
bag
application
Staging
in cooler
(inside)
Storage
in cooler
No
MA
required?
Yes
MA bag
application
Staging for
loading
Loading
Transport
to DC
No
Transport
to store
Unloading
at DC
Holding on
DC dock
Storage
at DC
Staging on
DC dock
Loading
Unloading
Holding
on dock
Storage in
walk-in
cooler
Stocking
display
Display
Strawberry Cold Chain Process Map
3
CALIFORNIA STRAWBERRY COMMISSION
Harvest
Strawberries are harvested and packed in the field. They are most often packed directly into plastic clamshell
containers held in corrugated flats. This packaging holds the berries through to the consumer. The flats are
accumulated and palletized in the field.
The strawberry temperature at harvest even in cooler growing areas is relatively high compared to optimum
temperature of 32°F to 34°F required for maximum quality and shelf life. Once the strawberry is harvested and cut off
from its source of water and nutrients, the process of degradation begins, and cooling as soon as possible to
minimize the rate of degradation is critical.
Potential Cold Chain Problems:
• Delay in cooling is the most common problem in cold chain management for strawberries at harvest. Some delay is
inevitable as it is necessary to accumulate the fruit in the flat, accumulate enough fruit to build the pallet and
accumulate enough pallets to justify a trip from the field to the cooler.
• Studies indicate a significant loss of shelf life if cooling is delayed over 2 hours after harvest. See graph below.
% Marketable
100
80
60
40
20
0
2
4
Hours cooling delay
6
8
Delay in strawberry cooling vs. marketability
Provided by University of California Division of Agriculture and Natural Resources
• Direct exposure to sunlight during the accumulation of the fruit in the field can also raise the strawberry
temperature.
Recommendations:
• Move fruit from field to cooler within 2 hours or less after harvest, preferably within 1 hour.
• Cover tops of pallets in order to avoid exposing strawberries on the top tier of flats to direct sunlight and wind while
accumulating fruit in the field.
BEST HANDLING PRACTICES FOR STRAWBERRIES
4
Transportto Cooler
The pallets of strawberries are normally transported to the cooler on flat bed trucks.
Potential Cold Chain Problems:
• Delays in moving the product from the field to the cooler result in holding the fruit at high temperatures longer than
necessary.
• Exposure to sun and warm air while traveling at high speeds can warm the fruit above the harvest temperature and
cause dehydration.
Recommendations:
• Drivers must always go directly from field to cooler and avoid stops for breaks or refueling while transporting the
strawberries.
• Limit the time harvested strawberries are exposed to field temperatures by transporting to the cooler within 2 hours
or less after harvest.
5
CALIFORNIA STRAWBERRY COMMISSION
Staging for Cooling
The pallets of strawberries are removed by forklift from the flatbed truck and staged for cooling after they arrive at
the cooler.
Potential Cold Chain Problems:
• Delays in moving the fruit into the cooler can occur especially during peak harvest periods. Trucks with
strawberries from the field may sit while waiting to be unloaded at the cooler. This extends the time from harvest to
cooling, keeping the strawberries well above optimum temperature for longer than necessary. The product may
also warm further due to exposure to the sun during this time.
• Delays in beginning the forced-air cooling process often occur once the pallets are moved from the trucks to inside
the cooler. This delay can be due to lack of space in the forced air tunnels, problems in coordinating labor, lack of a
sense of urgency on the part of cooler employees or lack of understanding of the importance of minimizing the time
from harvest to cooling.
• It is important to note that while better than holding the pallets outside on the trucks, significant shelf life and quality
loss can occur while holding pallets received from the field inside the cooler prior to forced-air cooling. While fruit
around the outside edges of the pallet will cool quickly, fruit at the center of the pallet will take many hours to reach
the optimum temperature while waiting for the forced-air cooling process to begin.
Recommendations:
• Move product from the trucks to the cooler immediately upon arrival.
• Use shade structures to cover the trucks or pallets if product must be held outside on the trucks due to constraints
of the facility.
• Begin forced-air cooling as soon as possible after the fruit arrives. Removing the field heat from throughout the
pallet as quickly as possible is critical for maximum shelf life and quality.
• Follow the steps described in the next section on forced-air cooling to maximize throughput while ensuring
proper cooling.
BEST HANDLING PRACTICES FOR STRAWBERRIES
6
Forced-Air Cooling
Forced-air cooling is used to quickly remove field heat from the strawberries. This technique is simple and effective,
but requires careful attention to detail to ensure maximum effectiveness.
Potential Cold Chain Problems:
• Delays in starting the cooling are often a problem as mentioned in previous sections. Sometimes the delay
continues while the pallets of strawberries are lined up in the forced-air cooling tunnel, ready to be cooled, but for a
variety of reasons, cooler personnel do not turn on the fans or seal the tunnel immediately. This means that fruit on
the interior of the pallet will remain at or near harvest temperatures longer than necessary. The heat will be
removed very slowly until there is significant air movement through the pallet.
• Failure to properly seal the forced-air tunnel. The only openings that air should be drawn through are the vents in
the strawberry flats. Openings around the base of the pallet and between the tarp over the air channel between
pallets will result in short-circuiting of the airflow and less air will flow across the fruit, slowing the cooling process.
• Terminating the cooling process too soon or too late. Often cooler personnel will terminate cooling based only on
time on the forced-air cooler instead of measuring the temperature. While this may sometimes work, it often leads
to incomplete cooling. Less commonly, cooler personnel will leave the fruit on the forced-air tunnel longer than
necessary which can lead to unnecessary water loss.
• Setting air temperature too cold. Attempts to speed cooling by using air temperatures lower than 30-31°F can
result in damage to the fruit. This is because the fruit near the box air vents on the outside of the tunnel will
quickly reach the same temperature of the air while fruit on the sides of the pallet facing the inside of the tunnel will
reach the air temperature only when the cooling process is nearly over. The result is freeze-damaged fruit in the
sections of the pallet that cool the fastest.
Recommendations:
• Set up pallets, seal and run the forced-air cooler as soon as pallets are brought to the cooler. Avoid any delays to
beginning the movement of air through the pallets.
• Train cooler personnel on the principles of forced-air cooling, emphasizing the importance of sealing all openings
around the pallet that air could be drawn through instead of being forced through the boxes of strawberries.
7
CALIFORNIA STRAWBERRY COMMISSION
• Measure strawberry temperature to determine when to terminate the cooling process. Use a calibrated probe
thermometer to measure the strawberry pulp temperature in a box on the inside of the tunnel at the end of the
tunnel opposite the fan to determine if the strawberries have been cooled to 34°F or lower before removing the
pallets from the cooling tunnel. This is normally the slowest cooling location. See diagram below.
Suction fan
Leave no gaps
between pallets
Cooler wall
Leave no gaps between
tarp and pallets
Air fl
ow
Air flow
Tarp
Air flow
Monitor temperature
here to determine when
to stop force-air cooling
Cover all openings around base of pallets
Diagram of forced-air tunnel indicating proper location to monitor temperature
• Maintain the temperature of the air in the forced-air cooler at 31-32°F. Attempts to speed cooling by using lower
temperatures will lead to localized freeze-damage to the fruit.
• Remember that cooling the strawberries as soon as possible after harvest is one of the most effective ways to
minimize water loss as air at 70°F can hold about 4 times as much water as air at 32°F.
Leave no gaps
between tarp and pallets
Leave no gaps
between pallets
Cover all openings
around base of pallets
BEST HANDLING PRACTICES FOR STRAWBERRIES
8
Modified Atmosphere Pallet Bag
Normal air contains about 0.03% carbon dioxide (CO2 ). Modifying the atmosphere around the strawberries to include
10-20% carbon dioxide will very effectively inhibit the growth of fungus. Sealed pallet bag systems designed to
maintain high carbon dioxide atmospheres are used on a large percentage of strawberries shipped in North America.
While very effective in inhibiting fungal growth, modified atmospheres are a supplement to good cold chain
management, not a substitute for it. Also, as the pallets must be sealed to maintain the atmosphere, the pallet bags
inhibit airflow so extra attention must be paid to temperature management.
Potential Cold Chain Problems:
• The strawberries are very difficult to cool once the modified atmosphere bag has been placed on the pallet. If they
are not cooled properly prior to the application of modified atmosphere, the strawberry temperature will never
reach the proper temperature at any point during distribution. High temperatures may also cause excessive
accumulation of carbon dioxide in the pallet bag causing off-odors and off-flavors.
Recommendations:
• Cool strawberries to 34°F or lower prior to application of the modified atmosphere bag. It is not possible to
efficiently cool the strawberries once the pallet bag is in place.
• Use a probe thermometer to verify proper temperature before application of the modified atmosphere pallet bag.
9
CALIFORNIA STRAWBERRY COMMISSION
Storage at Cooler
After cooling, strawberries may be held for a few hours up to 1-2 days at the cooler prior to shipment. Most fruit is
shipped within 24 hours of harvest.
Common Cold Chain Problems:
• Damage to doors or strip curtains in the cooler can result in leakage of warm air from dock or office areas into the
cold storage areas.
• Variations in temperatures from location-to-location or over time within the cooler may occur due to poor design,
problems with maintenance of the refrigeration equipment, and movement of people, pallets and forklifts
especially near doors. These variations in temperature often are not detected with the small number of sensors
generally installed as part of the refrigeration system in the coolers.
Recommendations:
• Proper and scheduled maintenance of doors and strip curtains and repair of forklift-damaged walls must be part of
the standard operating practices for all coolers.
• Periodically conduct detailed thermal mapping of the cold storage areas by placing temperature monitors in a 3D
grid throughout the cold storage areas. This will help identify the variation in temperature from location-to-location
within the cooler and over time. Appropriate corrective actions such as making repairs or restricting the storage of
strawberries in certain locations (i.e. near doors with high traffic or leakage) can be implemented based on
the findings.
• Maintain cooler temperature at 32°F.
BEST HANDLING PRACTICES FOR STRAWBERRIES
10
Staging for Loading
Prior to loading into the trailer for shipping, the pallets of strawberries are often moved from the storage area and
staged on or near the loading dock.
Potential Cold Chain Problems:
• In some coolers, the dock area is warmer than the storage areas. This may be due to poor design, inadequate
refrigeration capacity or leakage of warm air from dock doors.
Recommendations:
• Inspect and repair seals around dock doors on a routine basis.
• Leave dock doors closed unless a trailer is being loaded or unloaded.
• If the dock area cannot be properly refrigerated, stage loads in the cold storage area instead. Load pallets directly
into the trailer to avoid holding product in dock area.
• Shut off trailer refrigeration unit if the dock temperature is over 41°F to avoid sucking warm air into the trailer.
• Periodically conduct detailed thermal mapping of the dock area by placing temperature monitors in a 3D grid
throughout the dock area to help identify the variation in temperature from location-to-location and over time.
Appropriate corrective actions such as making repairs or restricting the storage of product in certain locations can
then be implemented based on the findings.
11
CALIFORNIA STRAWBERRY COMMISSION
Preparing Refrigerated Trailer
Proper use of refrigerated trailers is critical to ensure quality and shelf life for strawberries. Unlike fixed storage
facilities like strawberry coolers and distribution centers (DC) cold rooms, maintaining proper temperature in trailers
poses unique challenges for both refrigeration manufacturers and users. Road weight limitations, fuel consumption,
shape and size constraints, and environmental factors make using refrigerated trailers a challenge that requires
excellent attention to detail on every shipment.
Proper trailer preparation is key to successful shipments.
Common Cold Chain Problems:
• Refrigerated trailers are frequently damaged from loading and unloading product with forklifts. The walls, ceiling,
door seals and air chute are particularly vulnerable. Any damage to these areas can result in inhibited airflow or
leakage of warm air from outside the trailer.
• Improper refrigeration settings, particularly the temperature setpoint and refrigeration mode, can result in transit
temperatures that are too warm or too cold.
• Failure to properly pre-cool the trailer results in heat from the trailer body raising the air temperature and/or being
conducted into the fruit.
Recommendations:
• Inspect the trailer to ensure it is in good repair.
- Sidewalls, ceiling and floor should be free of holes or unrepaired damage.
- Air chute should be properly attached to the reefer unit and ceiling and should be free of cuts and holes.
- Floor should be clean and free of debris.
- Door seals should be free from damage that would allow air to pass through.
- Trailer should be free of any objectionable odors.
- If the trailer does not meet the conditions above, it should be rejected and replaced or repaired.
• Pre-cool the trailer.
- Set trailer reefer at 32°F on continuous mode, close doors and run for a minimum of 30 minutes. These settings
should be used during transport too. However, some transportation companies and shippers may choose a
slightly lower temperature.
- Do not use fuel saver mode. This mode reduces fuel consumption, but results in large, potentially damaging
swings in temperature and poor temperature control.
- Using a calibrated probe thermometer verify the wall temperature is 32°F or below. If not, continue cooling. If
additional cooling does not bring the temperature down, reject trailer.
BEST HANDLING PRACTICES FOR STRAWBERRIES
12
Loading the Refrigerated Trailer
The pallet loading pattern used to load the trailer is important to ensure proper air circulation in the trailer.
Common Cold Chain Problems:
• Loading pallets so that they are in direct contact with the wall allows heat to be conducted from the outside of the
trailer into the fruit and blocks the airflow required between the wall and the product.
• Placing the temperature monitor directly on the wall may result in readings that do not accurately reflect the air
temperature in the trailer.
• Loading pallets that are above the redline (usually about 9-12 inches from the ceiling) will inhibit the airflow to the
door end of the trailer.
Recommendations:
• Load pallet using a centerline-loading pattern (away from walls). (See diagram below) Use spacers (corrugated
or airbag) between the pallets and the walls to keep the product from shifting during transit.
• Pallet height should not exceed the trailer red line that is usually 9-12 inches from the ceiling of the trailer.
• Use load locks after the last pallet to prevent load shifting during transit.
• Attach temperature monitor to the last pallet at eye level.
• To avoid vibration damage in mixed trailer loads, do not load strawberries on the rear of a mixed load.
FIGURE 5
40”40”
40” 48”
Pallets Centerline Loaded
40” 40” 40” 48”
48” 48”
Pallets Loaded Against the Trailer Wall
Loading pattern diagram
13
CALIFORNIA STRAWBERRY COMMISSION
Unloading at Distribution Center (DC) / Holding on Dock at DC
Upon arrival at the distribution center, the pallets are typically unloaded to a receiving dock. Especially in older DCs,
the receiving docks are often maintained at temperatures well over the optimum temperature for strawberries. For
example, produce receiving docks with temperatures of 45-60°F are common.
Potential Cold Chain Problems:
• Unloading the trailers on an un-refrigerated or under-refrigerated dock with the trailer refrigeration unit running will
suck warm air from the dock into the trailer and warm the strawberries. Running the trailer on a well-refrigerated
dock is acceptable and in warm climates, desirable.
• Holding product on the receiving dock prior to placement in the cold storage area. This is sometimes done for
purposes of counting or quality inspection. At some DCs, very high pallets are broken down to fit in the DC’s racking
system. Under some circumstances, the product may be held on the receiving dock for several hours. This is
usually due to problems in coordinating labor, timing of employee breaks or miscommunication.
Pulp Temperature
The temperature of the product in the center of the pallet of strawberries will rise relatively slowly, however, the
temperature of strawberries around the outside of the pallet and especially in the corners will rise quickly. See the
diagram below which illustrates changes in temperature when product is left on an under refrigerated dock.
55
50
45
40
35
0.5
1.5
Pulp Temperature
1
55
50
45
40
35
0.5
2.5
2
1.5
1
3.5
3
2.5
2
4.5
4
3.5
3
5.5
5
5.5
5
7.5
7
Hours
4.5
4
6.5
6
6.5
6
Hours
8.5
8
7.5
7
9.5
9
8.5
8
10
9.5
9
10
Rate of warming of strawberries in different locations in pallet after moving from 35F trailer to 50F dock.
Recommendations:
• Turn off refrigeration unit while unloading if the dock is above 41°F.
• Unload pallets of strawberries directly from the trailer to the cold storage area without holding the pallet on the
receiving dock. Many DCs use space inside the cold storage area near the door or space between racks to hold the
product for inspection prior to placing it in the racks.
• Train DC employees to minimize time on the dock if space or procedures will not allow unloading directly to the cold
storage area.
• Remove modified atmosphere pallet bags upon arrival at DC.
BEST HANDLING PRACTICES FOR STRAWBERRIES
14
Storage at DC
After arrival at the distribution center, strawberries are held in cold storage until they are needed for an outbound
shipment to the retail store. Except in old and/or poorly maintained DCs, this step in the cold chain is seldom a
problem.
Common Cold Chain Problems:
• Damage to doors or strip curtains in the DC can result in leakage of warm air from dock or office areas into the cold
storage areas.
• Variations in temperatures from location-to-location or over time within the cold storage area may occur due to poor
design, problems with maintenance of the refrigeration equipment, and movement of people, pallets and forklifts
especially through doors. These variations in temperature often are not detected with the small number of
sensors generally installed as part of the refrigeration system in the coolers.
Recommendations:
• Proper and scheduled maintenance of doors and strip curtains and repair of forklift-damaged walls must be part of
the standard operating practices at all DCs. Savings in product shrink and energy consumption offsets the cost
of repairs.
• Periodically conduct detailed thermal mapping of the cold storage areas by placing temperature monitors in a 3D
grid throughout the cold storage areas to help identify the variation in temperature from location-to-location within
the cooler and over time. Appropriate corrective actions such as making repairs or restricting the storage of
strawberries in certain locations (i.e. near doors with high traffic or leakage) can be implemented based on
the findings.
• Optimal cooler temperature for storage of strawberries is 32°F.
15
CALIFORNIA STRAWBERRY COMMISSION
Staging for Loading at DC
In preparation for trailer loading, product is removed from the storage area in the DC and staged on the shipping dock
on a store-by-store basis. This means that the number of flats needed for an individual store are picked from the
storage area and are placed on a pallet of mixed products. The pallets of mixed products are held on the shipping
dock near the dock door where the trailer that will transport the product to the store is to be loaded.
Like the receiving dock (often there is only one dock used for receiving during half the day and shipping during the
other half), and especially in older DCs, the shipping docks are often maintained at temperatures well over the
optimum temperature for strawberries. For example, produce shipping docks with temperatures of 45-60°F are
common.
Common Cold Chain Problems:
• The staging process can take from about 30 minutes to several hours. Delays can be due to difficulties in
coordination of picking staging and loading; waiting for missing items; problems in coordinating labor, trucks or
trailers; and timing of employee breaks.
Recommendations:
• The most practical recommendation for DCs with under-refrigerated docks, short of installing new refrigeration
equipment, is to ensure that the time between the beginning of staging and the end of trailer loading is as short as
possible. This requires good coordination of product, labor and equipment.
• This step in the distribution process is problematic for most produce items at DCs where the dock is un-refrigerated
or under-refrigerated. There are few easy, cheap or practical solutions. Many DCs hold dock temperatures near
32°F. However, the lower temperatures can cause chilling injury on chilling sensitive products such as bananas
and therefore special handling steps are required for those products.
BEST HANDLING PRACTICES FOR STRAWBERRIES
16
Transportto Store
Strawberries are often shipped from the DC to the store in trailers with mixed loads. The trailers usually deliver
product to two or more stores. The trailers are usually loaded by store to facilitate the drop offs. With a few exceptions,
the time from DC to store is usually 24 hours or less. Depending on the company, the produce items may be
transported on a trailer with more than one temperature zone. The combination of zones may be frozen/fresh/dry,
frozen/fresh or fresh/dry.
Strawberries placed too close to
the discharge vent of the refrigeration
unit may sustain freeze damage.
Cold air leakage from freezer section or warm
air from dry section can damage strawberries.
Frozen
Chiller
Dry
Diagrams of multizone trailers
17
CALIFORNIA STRAWBERRY COMMISSION
Common Cold Chain Problems:
• Trailer damage results in poor temperature control. The trailers used to transport product from DC to store tend to
be loaded and unloaded much more frequently than trailers used to transport product from cooler to DC. They also
tend to spend more time on city streets vs. highway. These two factors result in more damage to the DC’s fleet
of trailers.
• The product temperature will always be compromised when the product is loaded against the wall of the trailer and
this problem is greatly compounded if it is loaded against an area of the wall that has been damaged.
• Leakage of cold air from around (especially under) the moveable bulkheads separating the frozen from the fresh
sections can cause freezing damage on the strawberries in multi-zone trailers. Likewise, leakage of warm air from
the dry section can cause warming of the strawberries.
• Strawberries placed close to the discharge vent of the refrigeration unit may be damaged by freezing. The air
discharged from the refrigeration unit may be well below freezing. The air warms as it mixes with the trailer air, but
product close to the discharge vent will be exposed to lower temperatures. This is more often a problem with multizone trailers where the second or third section is used for the fresh products.
Recommendations:
• Prepare trailers as described in Preparing Trailer for Loading section above.
• Establish procedure for routine and frequent inspection and repair of trailer damage and damage to movable
bulkheads. Repair or replace as necessary.
• Avoid loading pallets against the wall of the trailer to avoid heat conduction through the wall and into the pallet.
• Avoid loading strawberries against the bulkheads, especially near the floor where they are susceptible to freezing
or warming due to leakage under the bulkheads.
• Avoid loading strawberries on the top of pallets close to the discharge air vent from the refrigeration unit
(evaporator coil) to minimize freezing risk.
BEST HANDLING PRACTICES FOR STRAWBERRIES
18
Unloading at Store/ Holding on Dock at Store
Upon arrival at the store the driver normally unloads the product. The receiving process varies greatly by company,
division and sometimes store. At this point in distribution, the product is no longer neatly palletized and the strawberry
flats will be exposed on several sides, allowing them to warm faster than they would have at earlier stages in
distribution.
Common Cold Chain Problems:
• Often the driver will unload and leave the product on the receiving dock allowing it to warm until store personnel put
the product in the cooler. This problem is exacerbated when the product is dropped late at night or in the early
morning hours when there are few or no store employees available to put the product in the cooler.
• There is often a delay in putting the strawberries in the cooler after delivery to the store, particularly under
circumstances where a count of product must be made upon delivery (i.e. where the product is supplied by
a wholesaler).
Recommendations:
• The driver should unload the perishable items such as strawberries directly into the produce cooler.
• Any inspection or count that must be done upon arrival should be done in the walk-in cooler.
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CALIFORNIA STRAWBERRY COMMISSION
Storage in Walk-In Cooler at Store
Most stores do not receive shipments of produce daily, so they must keep up to 2-3 days inventory stored in the walkin produce cooler.
Common Cold Chain Problems:
• Leaving the door to the produce walk-in cooler open is one of the most common cold chain problems at the retail
level. Even during cool weather this will cause a significant increase in temperature. The problem will be less
critical if strip curtains are used, but even with strip curtains the cooler temperature will rise.
• Damaged strip curtains allow warm air to enter the cooler. There are times when the cooler door must be open to
move product in and out. Strip curtains minimize the amount of warm air entering the cooler during these times
without inhibiting movement of people and carts. Strip curtains are often in poor condition due to wear and tear, and
often employees deliberately cut the strips to make it easier to pass through the curtain.
• Often the temperature of the walk-in coolers is high simply because the refrigeration unit setpoint is too high or
because the unit has not been maintained properly. Wall thermometers commonly used to monitor the temperature
are often inaccurate and improperly placed.
• Warm and cold spots exist in the walk-in cooler, even under the best of circumstances, due to the movement in and
out of the cooler. The temperature near the door will tend to be higher than the rest of the cooler. Likewise, the air
very close to the discharge from the refrigeration unit (evaporator coils) may be below freezing.
Recommendations:
• Walk-in cooler doors should be kept open only when necessary to enter or exit the cooler. This may be an
inconvenience for store employees, but it will improve product temperature control significantly.
• Strip curtains should be used on the walk-in cooler doors. The condition of the strip curtains should be monitored as
part of routine refrigeration maintenance and they should be repaired or replaced as necessary.
• Store managers should emphasize these recommendations as part of their standard operating procedures.
Avoid storing strawberries close to the cooler door or on racking that would put the strawberries within 3 feet of the
discharge from the refrigeration unit (evaporator coils).
BEST HANDLING PRACTICES FOR STRAWBERRIES
20
Stocking and Display
Temperature management during this last step in the cold chain is challenging. Efforts to maintain good temperature
control, maximize quality and minimize shrink are complicated by the necessity to display the strawberries in a
manner that will encourage maximum sales.
Strawberries have traditionally been merchandised in unrefrigerated displays. Unrefrigerated displays have the
advantage of flexibility in adding space during peak selling seasons. As strawberries are highly temperature
sensitive, many progressive supermarket chains are changing to refrigerated displays to reduce shrink and improve
customer satisfaction. In-store research has indicated that the use of properly positioned and sized refrigerated
strawberry displays can improve unit sell-through by almost 3 percent.
Common Cold Chain Problems:
• Failure to proactively manage unrefrigerated display. This results in poor rotation and the associated quality
problems.
• Improper supply air setpoint on refrigerated display.
• In refrigerated fixtures, improper stocking can disrupt proper airflow, which results in higher product temperatures.
For example:
- Overstocking the case will disrupt the air curtain and allow warm store air to enter the case.
Supply air vent
Obstructed air curtain permits
warm store air to enter the case
Return air vent
- Stacking packages of strawberries over the return air vent will disrupt the airflow and inhibit air circulation.
Supply air vent
Air curtain weakened or
disrupted by product blocking
the return air vent allowing
warm store air to enter case
Return air vent
Blocked return air vent inhibiting airflow
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CALIFORNIA STRAWBERRY COMMISSION
Recommendations:
• When using un-refrigerated displays, manage the display proactively. Check display and rotate product every 2
hours to keep display full and maintain product quality.
• For refrigerated displays, follow the steps below to ensure the optimum temperature performance:
• Verify that the supply air temperature is at 32-35°F using a calibrated probe thermometer. If it is not, check again
approximately one hour later in case the unit was in defrost cycle when first checked. If the temperature is below
32°F or above 35°F, request maintenance.
• Stock cold strawberries. Do not allow the strawberries to warm while stocking as the refrigerated cases are
designed to maintain product temperature. They are not designed to efficiently reduce the strawberry temperature
from room temperature to 32°F.
• Do not block the supply air vent or the air curtain. Store employees will often stack the clamshells too high, either
directly blocking the supply air vent or disrupting the air curtain that requires an uninhibited path from the supply air
vent to the return air vent. Disrupting the air curtain will allow warm air from the store to enter the case.
• Do not block the return air vent. The airflow into the return air vent should be uninhibited by packages, signage, etc.
Employee training and using front fences to keep product away from the return vent will help.
Unobstructed air flow
Supply air vent
Return air vent
Proper airflow in refrigerated display fixture
BEST HANDLING PRACTICES FOR STRAWBERRIES
22
Additional Information
General Postharvest Information
• Kader, Adel A, 1991. Postharvest Technology of Horticultural Crops, 3rd Edition. Cooperative Extension,
University of California Division of Agriculture and Natural Resources Special Publication 3311, 192 pp.
• Gross et al., 2004. The Commercial Storage of Fruits, Vegetables and Florist and Nursery Stocks
USDA Handbook 66. Updated, online version: http://www.ba.ars.usda.gov/hb66/contents.html
• Mitchell, F.G., E. Mitcham, J.F. Thompson, and N. Welch, 1996. Handling Strawberries for Fresh Market.
University of California Division of Agriculture and Natural Resources Special Publication. 2442, 14 pp.
Forced Air Cooling
• Watkins, John B., 1990. Forced-Air Cooling, 2nd Edition, Queensland Department of Primary Industries.
Brisbane, 56 pp.
• Thompson, James and Knutson, Jerry. Forced Air Cooling of Strawberries in Clamshell Baskets.
Department of Biological and Agricultural Engineering, University of California, Davis.
Online at: http://ucce.ucdavis.edu/files/datastore/234-157.pdf
Refrigerated Transport
• Thompson, James F., Patrick E. Brecht, Tom Hinsch, Adel A. Kader. 2000. Marine Container Transport
of Chilled Perishable Produce. University of California, Division of Agriculture and Natural Resources,
Publication 21595, 32 pp
• Thompson, J. F., et al. 2004. AirTransport of Perishable Products. University of California, Division of
Agriculture and Natural Resources, Publication 21618, 22 pp.
• Thompson, J. F., et al. 2002. Refrigerated Trailer Transport of Perishable Products. University of California,
Division of Agriculture and Natural Resources, Publication 21614, 28 pp.
• Carrier Transicold: http://www.transicold.carrier.com
• Thermo King Corporation: http://www.thermoking.com
Refrigerated Display Fixtures
• Hill Phoenix: http://www.hillphoenix.com
• Hussmann Corporation: http://www.hussmann.com/Products/products.htm
• Kysor//Warren: http://www.kysor.com/home.html
• Tyler Refrigeration Corporation: http://www.tylerrefrigeration.com/index.html
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CALIFORNIA STRAWBERRY COMMISSION
California Strawberry Commission
MAINTAINING
QUALITY
OF FRESH
STRAWBERRIES
PO Box 269
Watsonville, CA 95077
831.724.1301 phone
831.724.5973 fax
[email protected]
www.calstrawberry.com
© 2011 California Strawberry Commission