potato storage management for quality potatoes roger brook extension engineer michigan state...
TRANSCRIPT
Potato Storage Management for Quality Potatoes
Roger Brook
Extension Engineer
Michigan State University
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
Things Affecting Potato Storage Environment
• Tuber respiration
• Heat transfer thru building
• Tuber variety and condition
• Disease
“ Respiration is, in a way, the opposite of photosynthesis. Energy stored in sugars is now released for use in maintenance of the tuber.”
Respiration
6O6O22 + C + C66HH12120066 6CO6CO22 + 6H + 6H22O + EnergyO + Energy
GlucosGlucosee
CarbonCarbonDioxideDioxide
WaterWater
(85% is heat)(85% is heat)
OxygenOxygen
Respiration Changes
• Over time• With tuber
temperature• With variety• With season
SEP NOV JAN MAR MAY
3030 55553535 4040 4545 5050 6060 6565
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)
Gas exchange in potato tubers
OO22
HH2200COCO22
COCO22
HH2200
HH2200
HH2200 COCO22
OO22
OO22
OO22
OO22
OO22
HH2200COCO22
Lenticel and epidermis of potato tuberLenticel and epidermis of potato tuber
Wall cross-section
TYPICAL WALL SECTIONTYPICAL WALL SECTION
vapor barriervapor barrier
PlywoodPlywood
1" extruded polystyrene1" extruded polystyrene
Insulation and structuralInsulation and structural
steel claddingsteel cladding
house wraphouse wrap
VentilationUniformity
•openings too small•underpile ducts too small•duct openings too large
•workable 750-1500 fpm
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
Sprinkler hose without endcap
Sprinkler hose - too many holes / too large
Sprinkler hose - correct holes / uniform distribution
Ventilation System Builds Pressure for Distribution
100 FT100 FT 30 FT30 FT
LoadingLoadingand and
Work Work AreaArea
PlenumPlenum
Fan RoomFan Room
Distribution DuctsDistribution Ducts
8ft. c/c8ft. c/c
Check distribution with food grade smokeCheck distribution with food grade smoke
End Cap
Thermometer,hanging onstring
PVC Solid Tubing4 - 8 ft. long
Monitoring TuberTemperature
Understanding Moist Air in Potato Storages
• dry air-water vapor mixtures
• relative humidity
• condensation and dew point
• humidification equipment
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
Effect of warming air on RH
50 50 ooFF95% RH95% RH
5555ooFF78% RH78% RH
60 60 ooFF66% RH66% RH
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.
Calculated Dewpoint RH in a Potato Storage
Dewpoint relative humidity, %CeilingSurfaceCondition
Wood orPolyurethane
Galvanizedsteel
Aluminumfoil
Still air R10 R20 R30 R40
91959799
85929596
82909395
HumidificationSystems
• High humidity – critical for curing process
– minimal weight loss
– maximum quality out of storage
• Need 1 gal. water per 800 - 1000 cfm of design air flow
Example of humidification required
System has two 5-HP fans:System has two 5-HP fans: need ~ 1 gal / 800-1,000 cfm airflowneed ~ 1 gal / 800-1,000 cfm airflow To determine humidifier capacity:To determine humidifier capacity: water = 32,000 cfm/1,000 cfm/gal = 32 gal.water = 32,000 cfm/1,000 cfm/gal = 32 gal. water = 32,000 cfm/800 cfm/gal = 40 gal.water = 32,000 cfm/800 cfm/gal = 40 gal.
Set water flow rate so that humidifier runs Set water flow rate so that humidifier runs 80-85% of the time80-85% of the time
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
High pressure nozzles
• moderate cost
• moderate maintenance
• some excess water in plenum
• moderate operating cost
• prone to nozzle plugging
High pressure air/water nozzles
• high cost
• high maintenance
• low excess water in plenum
• high operating cost
• excellent humidification
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
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
UNDERSTAND YOUR CROPCommon 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
PREPARE YOUR STORAGEStructural 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
PREPARE YOUR STORAGEVentilation 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
PREPARE YOUR CROP• Remove dirt and vines
• Grade to remove– rot and rocks– undesirable material
• Size for Market
• Record pulp temperature each load
Manage during HARVEST
• suberize ( wound healing )
– 55oF temperature
– 90+% relative humidity
– 10 - 14 days
• weight loss control
– humidification when fresh air
– ventilation air temperature
• modify for disease pressure
Harvest Conditions Influence Management
Dry SoilHarvest
Wet SoilHarvest
Warm weather(above 60oF)
coolhumidify
cooldry surf.
Cool Weather(50-60oF)
maintainhumidify
maintaindry surf.
Cold Weather(below 50oF)
warmhumidifyfresh air
warmdry surf.fresh air
Weight loss vs. Relative Humidity
0
2
4
6
8
10
12
0 1 2 3 4 5 6 7 8 9 10
75%
85%
95%
99.50%
Months in storageMonths in storage
% W
eig
ht
Lo
ss%
We
igh
t L
oss
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
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
Thank You -- Questions?
Roger Brook
Agricultural Engineering Department
210 Farrall Hall
Michigan State University
E. Lansing, MI 48840