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

brook@msu.edu