1. Potato Storage Management for Quality Potatoes
Roger Brook
Extension Engineer
Michigan State University
Potatoes are living organisms that interact with the surrounding environment. As such, they have the potential to deteriorate. It is the primary objective of the storage manager to provide an environment that will maintain quality throughout the storage season.

2. Potato Storage Ventilation
Use ventilation to control potato the storage environment
potato temperature
supply and/or control humidity
remove surface moisture
provide oxygen and remove CO2

3. Things Affecting Potato Storage Environment
Tuber respiration
Heat transfer thru building
Tuber variety and condition
Disease

4. Respiration
“ Respiration is, in a way, the opposite of photosynthesis. Energy stored in sugars is now released for use in maintenance of the tuber.”
6O2 + C6H1206
6CO2 + 6H2O + Energy
(85% is heat)
Oxygen
Glucose
Carbon
Dioxide
Water

5. Respiration Changes Over time With tuber temperature With variety
SEP
NOV
JAN
MAR
MAY
Over time
With tuber temperature
With variety
With season 30 35 40 45 50 55 60 65

6. The effect of stress on respiration
In general, any type of stress causes respiration to increase.
Stresses to watch for:
lack of fresh air (O2, CO2)
handling
temperature fluctuations
exhaust gases (CO, C2H4)
Notes:
1. Not 100% sure if lower oxygen causes increased respiration
but elevated CO2 definitely does.
2. Should included diseases in this list.
- disease organisms also respire and so accelerate the
depletion of oxygen and accumulation of CO2

7. Gas exchange in potato tubers
CO2 O2
H20
H20 O2
CO2
Notes:
1. Permeability of epidermis (periderm) probably accounts for
high rate of respiration
- although high rate is needed for suberization/periderm
formation
- sort of a chicken and egg situation.
H20
CO2 O2
H20
CO2 O2
Lenticel and epidermis of potato tuber

8. Wall cross-section vapor barrier steel cladding Plywood
house wrap
1" extruded polystyrene
Insulation and structural
TYPICAL WALL SECTION

9. Ventilation Uniformity
openings too small
underpile ducts too small
duct openings too large
workable fpm

10. Ventilation Uniformity
openings too small
size for 1000 ft/min
plenum too small
plenum air velocity no more than 85% of the underpile duct velocity
underpile ducts too small
size ducts so that air velocity is 85% of the air outlet velocity
duct openings too large
size outlet for 1000 ft/min

11. Sprinkler hose without endcap
Sprinkler hose - too many holes / too large
Sprinkler hose - correct holes / uniform distribution

12. Ventilation System Builds Pressure for Distribution
100 FT
30 FT
Distribution Ducts
Loading
and
Work
Area
8ft. c/c
Plenum
Fan Room
Check distribution with food grade smoke

13. Monitoring Tuber Temperature PVC Solid Tubing End Cap 4 - 8 ft. long
Thermometer,
hanging on
string

14. Understanding Moist Air in Potato Storages
dry air-water vapor mixtures
relative humidity
condensation and dew point
humidification equipment

15. Relative humidity
The ratio of the actual amount of moisture in the air to the maximum amount of moisture the air could hold at that temperature. Relative humidity (RH) is expressed as a percentage

16. Effect of warming air on RH

17. Surface temperature and condensation
condensation occurs at dewpoint temperature
potatoes or ceiling may be cooler than surrounding air; result can be “wet” surface.
Remedy: circulate air above bin or add insulation to ceiling.

18. Calculated Dewpoint RH in a Potato Storage

19. Humidification Systems
High humidity
critical for curing process
minimal weight loss
maximum quality out of storage
Need 1 gal. water per cfm of design air flow

20. Example of humidification required
System has two 5-HP fans:
need ~ 1 gal / 800-1,000 cfm airflow
To determine humidifier capacity:
water = 32,000 cfm/1,000 cfm/gal = 32 gal.
water = 32,000 cfm/800 cfm/gal = 40 gal.
Set water flow rate so that humidifier runs
80-85% of the time

21. Centrifugal humidifier
also known as “spinning disk”
most common; moderate cost
low to moderate maintenance
low operating cost
excess water in plenum
prone to mineral buildup

22. High pressure nozzles moderate cost moderate maintenance
some excess water in plenum
moderate operating cost
prone to nozzle plugging

23. High pressure air/water nozzles
high cost
high maintenance
low excess water in plenum
high operating cost
excellent humidification

24. Air washers high initial cost
may require additional humidifier in dry climates
design size and placement
minimum size by face velocity
minimum distance for air spread

25. POTATO STORAGE MANAGEMENT Looking for the Secrets
understand your crop
prepare your storage
prepare your crop
manage your system during HARVEST
manage your system during STORAGE

26. UNDERSTAND YOUR CROP Common Sources of Losses
breakdown due to disease
damage during harvest
equipment maintenance
harvest pulp temperature
weight and quality losses
cooling air temperatures
humidification
differences in respiration rates

27. PREPARE YOUR STORAGE Structural Checks
Framing for decay and rot
Doors for good seals
Insulation for intact and dryness
infra-red thermometer in summer
Storage sanitation
steam clean
surface sanitize

28. PREPARE YOUR STORAGE Ventilation Checks
Thermometers and thermostats for accuracy
Humidifiers for operation and water flow
Fans motors for operation and lubrication
Fresh air doors for operation and lubrication
Control systems for correct functions
Electrical systems adequate voltage and safety
Ducts in need of repair or replacement

29. PREPARE YOUR CROP Remove dirt and vines Grade to remove
rot and rocks
undesirable material
Size for Market
Record pulp temperature each load
Understand moist air psychometrics to
* help minimize pressure bruise
* help minimize weight loss

30. Manage during HARVEST suberize ( wound healing ) 55oF temperature
90+% relative humidity
days
weight loss control
humidification when fresh air
ventilation air temperature
modify for disease pressure

31. Harvest Conditions Influence Management

32. Weight loss vs. Relative Humidity12 10
75% 8
85%
% Weight Loss 6
95% 4
99.50% 2 1 2 3 4 5 6 7 8 9 10
Months in storage

33. Manage for Disease / Decay Conditions
dry tuber surfaces
lower RH helps some
cool tubers quickly
watch temperature difference
manage humidity - condensation
keep air moving
through the pile
over the pile

34. Manage during STORAGE cooling versus holding
cool rapidly after suberize
control temperature difference
don’t overcool early
holding conditions
38oF seed/table stock
95% relative humidity
fresh air every day
will vary with physiological age

35. Thank You -- Questions? Roger Brook
Agricultural Engineering Department
210 Farrall Hall
Michigan State University
E. Lansing, MI