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 CO 2

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

Respiration “ Respiration is, in a way, the opposite of photosynthesis. Energy stored in sugars is now released for use in maintenance of the tuber.”

6O 2 + C 6 H 12 0 6 6CO 2 + 6H 2 O + Energy (85% is heat) Oxygen Glucose Carbon Dioxide Water

Respiration Changes • Over time • With tuber temperature • With variety • With season

SEP NOV JAN MAR MAY 30 35 40 45 50 55 60 65

The effect of stress on respiration • •

In general, any type of stress causes respiration to increase.

Stresses to watch for:

– lack of fresh air (O 2 , CO 2 ) – handling – temperature fluctuations – exhaust gases (CO, C 2 H 4 )

Gas exchange in potato tubers

O 2 H 2 0 CO 2 O 2 H 2 0 O 2 O 2 H 2 0 CO 2 O 2 CO 2 H 2 0 O 2 CO 2 H 2 0 Lenticel and epidermis of potato tuber

Wall cross-section

steel cladding vapor barrier Plywood house wrap 1" extruded polystyrene Insulation and structural TYPICAL WALL SECTION

Ventilation Uniformity

• 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 FT Distribution Ducts 8ft. c/c 30 FT Loading and Work Area Plenum Check distribution with food grade smoke Fan Room

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

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 o F 95% RH 55 o F 78% RH 60 o F 66% 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

Ceiling Surface Condition Dewpoint relative humidity, % Wood or Polyurethane Galvanized steel Aluminum foil Still air R10 R20 R30 R40 91 95 97 99 85 92 95 96 82 90 93 95

Humidification Systems • 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: 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

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 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

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

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

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 ) – 55 o F 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

Warm weather (above 60 o F) Cool Weather (50-60 o F) Cold Weather (below 50 o F) Dry Soil Harvest

cool humidify maintain humidify warm humidify fresh air

Wet Soil Harvest

cool dry surf.

maintain dry surf.

warm dry surf.

fresh air

Weight loss vs. Relative Humidity

12 10 8 6 4 2 0 0 1 2 3 4 5 6 7 Months in storage 8 9 10 75% 85 % 95% 99.50%

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 – 38 o F 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 [email protected]