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Strategies for Storage Success


Ventilation, humidification and sprout control are important factors when storing your potato crop. Spud Smart has your crop covered with advice from the experts on best management practices, and a look at new products and technologies to enhance your storage success this season.

Ventilation: Top Tips and New Products

As potato growers expand their operations, they are requiring more storage facilities to hold their inventories, placing more demand on storage managers. This has increased growers’ needs for remote access to information in real time on storage environmental conditions. These demands are driving the next generation of potato storage control systems.

“What we are looking at right now is connectivity and transparency,” says Todd Forbush, an engineer with Techmark Inc, of Lansing, Mich. “We are making systems available through the Internet and smartphones by using text messaging and email to communicate information to storage managers as things are happening.”

Going Wireless

As a result, ventilation system controls in potato storage facilities now incorporate wireless technology to allow for web-based and mobile communications between the control systems, growers and potato storage managers.

A brand-new Techmark product to watch for at upcoming trade shows is AlarmPro, which can be adapted to any of Techmark’s storage installations. AlarmPro software automatically sends text messages or emails to storage managers when it detects problems with storage facilities. It can also automatically send emails to service agents. “We don’t dispatch service agents against the alarm, but it alerts us so we can call and verify that the problem has been resolved,” says Forbush.

Gorman Controls, located on Prince Edward Island, also has a new control system called MicroVent Vision, which has a touch screen interface and can be used with any web-enabled device to monitor and control the entire system: temperature, fan speed and carbon dioxide  purging. “Farmers told us they wanted everything to come through their Blackberries or iPhones, so we are providing that capability,” says Duane Gorman.

Another wireless control system on the market is Gellert Company’s Agri-Star Control Panel, which features a large, full-colour touch screen display with on-screen graphing capability, multimode carbon dioxide control, and plug and play, internet-ready communications capability that does not require any proprietary software for its operation.

“Our new control panel allows the potato grower or storage manager to quickly and easily build graphs and evaluate the data in real time, without having to download it and take it back to the laptop or something else,” says Nathan Oberg of Gellert. “By giving them that tool, they are able to make informed management decisions, which results in higher quality potatoes coming out of storages and more profitability for their operations.”

A carbon dioxide purge control system is also available for the panel, allowing storage managers to purge carbon dioxide while minimizing its effect on storage temperatures through better control of the air temperatures coming in.

Top-Notch Techniques

Although technology has its place, it can’t replace the skills and experience of growers and storage managers. Ventilation is crucial to maintaining correct temperature, relative humidity and air quality in potato storages, and should begin as soon as the potatoes are put into storage. This aids in the prevention of storage-related diseases or problems caused by large fluctuations in temperature.

Effective ventilation management of the crop is easier for growers if they know the quality of the crop they are putting into storage. And that’s a process that starts in the field. “One of the things that we suggest to our growers is that they flag situations, such as late blight, rotten tubers or weather extremes, throughout the growing season that might lead to rot in storage,” says John Walsh, potato storage specialist with McCain Foods Ltd. “If they have more than three flags up, they are going to be looking at drying—any less than that, and they must determine whether they can go right into curing or not.”

More growers are also adopting the idea of moving more air into the storage facility when they need to dry the crop or remove moisture or heat without adding the expense of investing in larger ventilation systems. One approach is to install fans in such a way as to double the capacity of air moving through the ducting and plenum. “Our minimum recommendation is one cubic foot per minute of air per hundredweight of potatoes, or 20 CFM per tonne,” says Walsh. “Growers would put in all the correct ducting and plenum size based on that one CFM per hundredweight, but then instead of putting in one CFM per hundredweight fans, they would put in up to double that capacity, and use variable frequency drives.”

Under normal conditions, growers can run the system at half speed, which still delivers the desired ventilation rate. Then, when problems arise, the grower can increase the fan speed up to 100 per cent capacity to get the required extra air. During periods when fans can run at half or quarter speed, such as during the winter months, the grower benefits from energy savings.

Another concept gaining popularity is the reheating of returned air. For growers with storage systems that ventilate with fresh air from the outside, the addition of appropriately-sized heaters that heat the returned air by one degree Celsius “fools” the system into thinking it’s too warm inside the storage facility. The system then opens up the doors to allow more fresh air in, which helps to drive down humidity without affecting the ambient heat inside the storage facility.

“If there’s rot present, there’s water in there, and that keeps the humidity high,” says Walsh. “What this does is force more fresh air into the storage facility, and essentially, for every degree, you can get about five per cent extra dry air, so instead of air at 92 per cent humidity it would be 87 per cent, and that will double the drying capacity of the storage through the ventilation system.” Some growers are also using dehumidifiers in the plenum for extra drying capacity, he notes.

A new product released this fall for reheating returned air is the KeepTheHeat exhaust system by Controlled Air of Winkler, Man. The integrated ventilation system exchanges heated, contaminated air inside the storage facility for clean air from the outside. The incoming fresh air travels at 2,000 cubic feet per minute through corrugated tubing, and is heated by the outgoing air to prevent any net heat loss. It can assist with carbon dioxide control, exhausting it without allowing excessively cold or hot air from outside to enter the storage facility. The unit helps to reduce heating costs and can also be used for humidity control and to improve air quality in work areas, exchanging humid or contaminated air from within with drier, fresh air from the outside at roughly the same temperature.

Although there are no easy answers when it comes to storing potatoes, knowing how to evaluate the crop is probably the most important step to achieving a healthy, saleable product. “Know the crop you are putting into storage because that will make all the other decisions fall into place,” says Walsh.

Best Management Practices for Effective Humidification

Humidification is an important aspect of potato storage management. High humidity is essential for optimum wound healing of tubers during the initial curing period, and during the entire storage period to minimize tuber weight loss and other problems.

As potatoes are comprised of about 80 per cent water, there is the risk that dry air in the storage facility will result in evaporation and tuber shrinkage. Therefore, high humidity must be maintained in the storage facility to prevent potatoes from releasing water into the air. Humidifiers are used in storage to maintain a minimum of 95 per cent relative humidity, but according to Walsh, anywhere from 95 to 98 per cent RH is a good number for healthy potatoes. However, if potatoes are not healthy, lower RH values may be required. “If you have rot problems, we typically recommend no drier than 80 per cent relative humidity. Under those circumstances, 85 per cent is a good drying humidity.”

Culling and Curing

Before humidification is introduced to the storage facility, diseased potatoes or those extensively damaged during harvest should be culled. If not removed, these tubers are often a prime source of disease in a pile during storage. “The healthier the crop that goes into storage, the better the chances of successful storage,” says Lukie Pieterse, an industry consultant.

“Further, it is important to remove excess soil and other forms of debris from the crop. Soil clods can block ventilation around tubers, which causes poor circulation in the pile, which in turn can lead to tuber rot in a relatively short time,” says Pieterse.

Following the culling process, stored tubers should be cured at temperatures between 10 and 15°C, and at a high relative humidity. During this phase, the storage manager should attempt to bring down the “field heat” of tubers if the crop was harvested during warm soil conditions. Most experts recommend a 95 per cent RH for two to three weeks during the curing stage of storage, says Pieterse.

The curing phase is extremely important for healing minor damage to the potato skin and allowing it to harden and mature. A protective, hardened suberin layer develops between the tuber surface and the interior tissue in three to five days, and cell regeneration can take place beneath this layer within 10 to 20 days if the potatoes are healthy. “The importance of this process can hardly be overemphasized. Successful curing plays a major role in the future health of stored potatoes. Wounded, uncured tubers are more susceptible to invasion by bacteria and fungi, which can easily cause healthy tubers to become diseased tubers,” says Pieterse.

Preconditioning and Cooling

High humidity in the storage facility during the first week or two is critical to prevent unnecessary tuber shrinkage. In the study entitled “Relative Humidity: A Key to Successful Potato Storage,” University of Idaho researchers Nathan Oberg, Nora Olsen and Gale Kleinkopf report that nearly half of the shrinkage in Shepody potatoes occurs during the first week after harvest. The study also reveals that the weight loss of potatoes stored over a six-month period at 90 per cent RH could be as much as nine per cent—double the weight loss of potatoes stored at 95 per cent over the same period. Assuming a storage capacity of 100,000 hundredweight and a value of $5.00 per hundredweight, a grower could lose $22,000 at the lower RH level.

Processing potato growers generally include a period of preconditioning in the storage facility, when they attempt to remove some of the sugar content from tubers. High sugar content usually results in darkened fries or chips. Walsh recommends that growers use the same temperatures as they would for curing—around 13 to 14°C. “They can leave [the potatoes] at those temperatures for a few weeks or longer if they have real colour issues,” he says.

There is a difference between a desirable RH and dampness or excessive condensation in the facility, notes Pieterse. In their report, University of Idaho researchers warn that condensation in the storage facility should be avoided, as free water in the plenum or on the ceiling above the crop is not necessarily an indication that the correct RH has been reached. “A variety of portable sensors are available to measure the actual RH in the facility, while many storage control panels have built-in sensors as well. Accurate measurement of RH is crucial, and most experts agree that the critical RH value is the plenum air before it is delivered to the pile,” says Pieterse.

Following the initial curing phase, the storage manager can take the pile into the cooling phase. While maintaining a high RH, the temperature is brought down gradually to between four and 10°C, depending on the kind of crop. “Some experts say the cooling air should not be more than 1.5°C cooler than the average pulp temperature of the tubers, while storage specialists usually recommend that the temperature be brought down by increments of 0.5 to 1.0°C per day, until the holding phase is reached. For the duration of the holding phase, the storage manager aims to maintain the desired temperature of the pile as well as a high relative humidity,” says Pieterse.

Management is Key

Over the past 25 years, evaporative humidifiers, or humidicells, have become the standard for use in potato storage. Humidicells are high-efficiency evaporative pads, which are saturated with water, and through which air is blown on the stored tubers for stable cooling.
Centrifugal and pump and nozzle systems also work well. Recent systems feature nozzles that produce a very fine mist, which evaporates quickly. These systems can offer effective and relatively low-cost humidification, although they must be cleaned frequently to prevent mineral deposits. Additionally, storage managers must ensure that the amount of free water emitting from the spray is controlled—too much water may leave the pile vulnerable to disease. Many systems now combine a humidification cell and supplemental spinners.

No matter what kind of humidification system is in use, storage managers must ensure it is in good working order before harvest. The University of Idaho report emphasizes that a worn cell or plugged spinners will seriously impede the system’s ability to supply sufficient water to maintain the correct RH. The report also recommends that RH sensors in the system be tested annually and calibrated or replaced by the ventilation system service provider. Sensors to measure RH should be placed in the plenum, but downstream of any fans and the humidifier itself, and any measurement from the top of the pile or in returned air streams should not be used as a basis for RH control.

Although many different types of humidification products and equipment are available, Walsh emphasizes that effective management of storage humidity is unique to every situation. “It’s one of those things that will depend a lot on where you are located and the products you grow. It’s something you have to work out with your ventilation designer.”

Sprouting Innovations: New Products

Sprout inhibitors help prevent or stop the sprouting of potatoes in storage. Growers can experience serious quality issues if sprouting is not managed. “Because the sprouts are growing from the tuber’s reserves, sprouting depletes the tuber,” says Barbara Daniels-Lake, a research biologist at Agriculture and Agri-Food Canada’s research facility at Kentville, Nova Scotia. “The tuber wilts and loses mass because part of its tissue is being broken down and reconverted into sprout tissue. That represents not only a loss in saleable quantity but also a deterioration of the quality of the potatoes because the sugars and textures change.”

Apart from using sprout inhibitors, there is little that growers can do to prevent sprouting, with the exception of choosing cultivars less inclined to sprouting early. “Cultivar is an important factor in sprouting, but the end use is what usually determines what cultivar you are going to choose,” says Daniels-Lake. “I think it’s important to know what to expect from the cultivar you choose including dormancy length.”

Controlling temperature is the only other influence a storage manager can exert to control sprouting, but it’s a double-edged sword. “If you store potatoes at colder temperatures, that delays sprouting because they may stay dormant a bit longer—but if you store them at colder temperatures and they are going to be made into french fries or potato chips, you may get low-temperature sweetening, which causes dark-coloured french fries or chips,” says Daniels-Lake. “There’s nothing simple in potato storage.”

The most commonly used active ingredient in sprout inhibition products worldwide is chlorpropham (CIPC), which is applied with specialized equipment to potato piles in storage. Walsh advises growers to wait at least two weeks before applying CIPC, and at that time it should be applied as quickly as possible. “The sooner you apply it the better, because the pile hasn’t settled very much and you will get better distribution of the fog,” he says. Even distribution of the sprout inhibitor throughout the pile is also aided by a reduction in fan speed during application to around 20 per cent of the maximum speed.

Solutions Provided by Nature

In the past, sprout management research and new product development was often spurred on by mounting consumer concern about pesticide residues and food safety, which led many in the industry to fear that products like CIPC might be banned.

Although that has not happened yet, the net result has been an increase in options for growers and potato storage managers, says Nora Olsen, an expert in sprout inhibition at the Idaho Potato Center for Research and Education. “Because CIPC is such a good product, we have struggled to find something as easy and effective,” says Olsen. “So, we have focused some of our research on alternatives, and how we can integrate them with established products like CIPC to make better control programs.”

Essential oils like clove, caraway or mint have a slight disadvantage to CIPC in that they are more costly than established treatments and also require multiple applications. They must also be applied after the potatoes have started to sprout. However, these products have proven useful for potatoes destined to be marketed in countries that do not allow the import of potatoes treated with CIPC.

Ethylene gas is another naturally occurring product, which is produced by most plants in small amounts as a plant growth regulator, so it has proven very effective for sprout inhibition. The use of ethylene gas as a sprout suppressant in potato storage facilities is growing rapidly, especially in European potato-producing countries. However, the use of ethylene gas hasn’t gained much of a foothold in North America, largely due to CIPC’s market dominance. Additionally, it can, in some instances, cause darkening of the potato flesh, which makes it unattractive for the french fry industry.

“Ethylene gas is effective at very low concentrations,” says Daniels-Lake, who is also a pioneer in the research on ethylene gas and has led several research projects on ethylene use in Canada. “When you put ethylene on as a sprout inhibitor you are just enhancing what the potato is already doing, and it’s non-toxic,” she says.

A new product, which should be registered for use in Canada very soon, is SmartBlock, a “green” biopesticide based on a naturally occurring compound that is found in many foods, such as yogurt, mushrooms, fish and soy. “It’s also a food-grade active ingredient that is already approved by the United States Food and Drug Administration as a direct food additive,” says John Immaraju, manager of International Product Development for AMVAC Chemical Corp., the producer of SmartBlock.

SmartBlock is applied after the potatoes begin to sprout. It then burns the sprouts off the tubers and restores dormancy, typically for a period of two to three months depending on the variety and storage temperature. SmartBlock contains 98 per cent of the active ingredient 3-decen-2-one, and is designed to be used in current warehouse storage thermal fogging systems. An emulsifiable concentrate formulation of SmartBlock for directly spraying on potatoes destined for the fresh market in potato packing operations is also being developed for the future.

Another new family of products registered for use in Canada this past year is the 1,4 product line developed by 1,4 Group. The products have been used successfully in the United States for the past 14 years.

The active ingredient in these products is 1,4-dimethylnaphthalene, a naturally occurring biochemical found in potatoes and other plants, which acts as a dormancy enhancer rather than a sprout inhibitor. The company offers three different products: 1,4SIGHT for potatoes in storage, 1,4SEED for seed potatoes and 1,4SHIP for potatoes to be shipped.

“DMN extends natural dormancy,” says Bill Orr, of 1,4 Group Canada “There are a lot of other benefits with DMN—it reduces water loss in potatoes, which helps reduce shrink and pressure bruising.”

Because its effect on potatoes can be reversed, 1,4SEED is the only dormancy enhancing product registered in North America for use on seed potatoes. “It helps to maintain the natural dormancy and firmness of seed potatoes without affecting vigour,” says Orr.

Sprout control is moving beyond reliance on one product, creating a multi-pronged approach, which may keep the industry viable and resilient should regulations or technologies change.

“It’s good to see some of these companies trying to make CIPC work better, and looking at technology with applications,” says Olsen. “This industry is a strong steward of sprout inhibition. It is looking at what products it can use and what it needs to do with temperatures in storage, and is taking a very integrated approach to get the most effective sprout control with all the tools that are available.” 

 Angela Lovell

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