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.

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 “ 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

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

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

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

Wall cross-section vapor barrier steel cladding 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 30 FT Distribution Ducts Loading and Work Area 8ft. c/c Plenum Fan Room Check distribution with food grade smoke

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

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

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

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 Understand moist air psychometrics to * help minimize pressure bruise * help minimize weight loss

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

Weight loss vs. Relative Humidity 12 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

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