Ontario must do a better job of preparing its potatoes for the consumer

Sunday, October 5, 2014

All too often, bags of Ontario table potatoes contain a few wet or rotten specimens. This could be prevented if proper curing and storing was combined with better packaging

by RALPH WINFIELD

Sad to say, my wife buys Prince Edward Island table potatoes in preference to Ontario potatoes whenever possible. All too often, Ontario table potatoes are not properly cured and stored, with the result that there will be two or three wet, rotting potatoes in a 10-pound (4.54 kilogram) bag.

There is no defendable reason for this to occur with the frequency that it does. The parameters for conditioning and storage are well known and can be achieved with available properly-sized equipment if operated by knowledgeable personnel.

Early crop potatoes that are harvested before full maturity can be held for several weeks if they are in sound condition. For table use, they can be held at 10 C in 85 to 90 per cent relative humidity air.
Late-crop potatoes that are intended for longer storage periods must be handled carefully to minimize mechanical damage that can result in several forms of loss. Severely damaged or disease-infected potatoes should not be stored.

Curing potatoes. Proper curing of potatoes before they are held in long-term storage is extremely important. The primary objective of curing potatoes is to improve their storage properties by making their skin firmer and tougher. This will decrease subsequent moisture loss and reduce the incidence of disease, while allowing them to recover from any digging or handling injuries.

The time, temperature and relative humidity requirements for curing potatoes are well documented. The facilities and equipment must be designed to provide the required air movement, ambient air temperature and relative humidity of the air. The operation of the total system must then be understood by the owner/operator.

The initial curing process can be completed in about two days at 20 C. The wound healing process will take 10 to 14 days at 13 to 16 C with 95 per cent relative humidity. Curing stops when the air temperature is reduced to 8 C.

The ultimate use of the crop and the length of storage period required after curing determines the optimum storage temperature and the relative humidity level.

Storing potatoes. Potatoes should be stored in bulk in a well-insulated facility, which excludes all light, to prevent the production of chlorophyll that will give the potatoes a very undesirable green colour. Insulation of the ceiling is especially critical to prevent any moisture condensation and water drip back onto the potatoes.

The air moving equipment must provide a continuous uniform flow of high-relative humidity air at a constant temperature to ensure that the potatoes do not shrivel or rot. Ventilation, air movement and exchange rate must also be regulated to ensure that carbon dioxide (CO2) levels will control the respiration rate of those "living" potatoes.

For short storage of table stock potatoes, the temperature can be in the 7-10 C range. If a sprout inhibitor is not used, the holding temperature must be reduced to about 4 C for a four-to-nine-month storage period. These values will vary somewhat with specific cultivars or varieties.

Packaging. After the storage period, the potatoes usually require bagging on-site in five or 10-pound bags for shipment on pallets to retail outlets. This should be done as closely as possible to shipment time. Just as importantly, the bags must have the capability for air exchange, but should also provide the customer the opportunity to see what they are purchasing. Opaque paper bags without a screened area on the back of the bag should be discouraged. They do not allow consumers to see what they are buying and block air exchange.

The purchasers of potatoes for processing into chips maintain a very high level of control over their purchase by demanding a wide range of product control by the producers. We, the individual purchasers, must be assured of the same level of product quality if we are going to continue to purchase local (Ontario) potatoes.

During my employment with Ontario Hydro, I assisted with the design of numerous commercial potato curing and storage facilities. The technology is readily available and so are the people who can design systems for even the relatively small table stock producers.

If you want my wife's business back, please ensure that she does not get soft or wet potatoes in bags and that the bags have a large enough screened area on the back that she can see what she is buying. The back panel of the last bag of potatoes we bought has the following storage tips beside the screened area on the backside of the bag: "Please turn me over, and store me in a cool, dry and dark place." Great advice well placed! BF

Agricultural engineer Ralph Winfield farms at Belmont in Elgin County.