Drying & Storage Equilibrium

Key differences growers must understand and put into practice when drying and storing sunflowers.

Kenneth Hellevang wrote the book on grain drying and storage. Drying sunflowers isn’t that much different from drying other grain types, says Kenneth Hellevang, an extension engineer and professor at North Dakota State University’s Department of Agriculture and Biosystems Engineering. What’s important to remember is all grain drying fundamentals apply, no matter what method is being used to dry the grain, he says. These fundamentals can be found in the NDSU Extension Service Publications written by Hellevang, Natural Air and Low Temperature Crop Drying (EB-35) and Grain Drying (AE-701). However, there are several important differences between drying sunflowers and other grains growers should understand, he says. The biggest being the grain’s weight.

The Waiting Game

“Sunflowers weigh less per bushel, so if you’re accustomed to drying a heavier crop like corn or wheat, you’ll find sunflowers dry quicker because there are less pounds of water that need to be removed.” 

When it comes to natural-air or low-temperature in-bin drying, Hellevang says he gets many phone calls from sunflower growers in the fall who have left harvest too late, and have run into trouble trying to dry their crops in cooler temperatures. 

“The moisture holding capacity of air is related to the air temperature. If we look at drying sunflowers in late October or November, it’s going to dry much slower, and differently, than drying wheat in September,” he says. “Farmers need to make sure they start early enough if they’re using a natural-air drying system.”

Although it may be tempting for growers to delay harvest and leave a sunflower crop in the field to dry, there is less drying ability in the air as temperatures fall in October and November. Temperatures near freezing have no drying ability left.

“Frequently I recommend people harvest [the crop] at a little higher moisture content than they might be inclined to, and then utilize the warmer air in October to dry, rather than try to dry in November,” says Hellevang.

“With temperatures down near freezing, we can’t just add a little supplemental heat and fix it. It’s very inefficient drying. If the farmer harvests too late in the fall, they will often need to hold [the crop] over winter and actually do the drying in the spring and early summer.”

Drying Differences and Moisture Rebound

When drying sunflowers in a high-temperature dryer, fires are a significant risk. With other grains, dryers may operate with minimal supervision, whereas constant monitoring is needed when drying sunflowers as the chaff, lint, and other debris associated with the grain is highly combustible.

“Being there to monitor that dryer becomes very important. When you look at what causes the actual fire, it’s typically some of the debris associated with the sunflower, or the sunflowers get hung up in the dryer, become over-dried and very combustible,” says Hellevang. “You can go from a bit of smoke to a big fire very quickly.”

Housekeeping is important with a high-temperature dryer according to Hellevang. If the dryer is not kept clean of debris, or if thegrain is not kept flowing through the dryer, fire risk is high.

Another point growers must keep in mind is due to the sunflower’s lighter weight, the drying rate is considerably different. It flows through the dryer quicker than heavier grains. “If we’re starting at 15 or 16 percent moisture, and we’re trying to dry it down to eight or 10 percent moisture, that drying process will occur quickly because we’re taking out less pounds of water than we would out of wheat or corn, or other types of grain,” says Hellevang.

Essentially, sunflower grain is comprised of two different materials – the outside hull and the kernel inside. These distinct materials create two different drying rates. The hull will dry rapidly, whereas the kernel will remain at a higher moisture content. This differential can create problems for sunflower growers when drying and storing grain.

For instance, the moisture content measurement can be off as the meter is more sensitive to the seed’s external portion. The meter may indicate the sunflower is at 10 percent moisture content, but the meter has been fooled, says Hellevang. The hull may be dry and the meter indicates 10 percent moisture, however, the kernel could be 12 or 13 percent moisture content. This phenomenon is called moisture rebound and is more frequently an issue associated with high-temperature drying.

To estimate moisture rebound, growers can take a grain sample from the dryer and place it in a covered container for 12 to 24 hours. Moisture moves from the kernel to the hull, creating a more uniform moisture content. The moisture meter will now present a more accurate moisture content reading.

“It’s not that there’s been any additional moisture added to the seed. Rather we have, over that period, established more of an equilibrium, and the moisture meter is getting a more accurate, true moisture content. That’s typically associated with high-temperature drying rather than natural-air or low temperature in-bin drying because [the latter] process takes place at a much slower rate,” says Hellevang.

Furthermore, an accurate reading for storage moisture content may require the same moisture rebound correction. 

Oilseeds Require Lower Moisture Content

Another aspect to consider is storage moisture content doesn’t necessarily correspond to the market moisture content. “The sunflower trade has been marketed based on a 10 percent moisture content as the standard,” Hellevang says.

Confection and non-oil seeds can be stored short-term at 10 percent moisture content, but going into warmer-season or long-term storage, Hellevang encourages growers to dry grain just below that value, to somewhere between nine and 10 percent moisture content.

Alternatively, oilseeds must be at eight percent moisture or lower, he says. “The eight percent is associated with a 40 percent oil content of the seed. Now, we’re seeing oil contents closer to 45 percent, which is good from a marketing and oil production standpoint, but it also means the storage moisture content needs to be lower – somewhere between seven and eight percent,” says Hellevang.

Geographic location also factors into the equation when it comes to storage moisture content. Growers farming in regions with warmer climates, such as Kansas and Texas, should be storing oilseeds between seven and eight percent, says Hellevang.

Northern regions, such as North Dakota and into Canada, have cooler temperatures during the fall and winter, so oilseeds can be stored during those months at higher moisture contents. However, storage into late spring or the following summer, requires oilseeds to be below market moisture content.

Growers could also focus more on managing stored grain temperatures by cooling grain in the fall and winter. In northern regions, bring grain temperatures down to just below freezing, roughly 30°F (-1°C). In southern climates, a realistic goal is 40°F (4.4°C) or cooler. For storing grain through warmer temperatures, such as the following summer, the target is to keep the grain as cool as possible, says Hellevang.

Another, often overlooked, aspect of storage management is for growers to cover the fan or air duct when not in use. If the fan or air duct is left uncovered, a natural chimney effect can be produced. When wind blows and hits that opening, the grain will be ventilated and warmed, much like running the aeration system.

“Both the blowing wind and this natural chimney effect will warm the grain in storage, which makes the grain more susceptible to insect infestations. Or if we’re marginal on moisture content, and a little on the damp side, it increases the potential for mold growth as well,” says Hellevang.

In general, Hellevang recommends growers conduct a thorough evaluation of stored grain conditions every couple of weeks when outside temperatures are warm. In the winter months, stored grain should be checked every two to four weeks, he says.

Ultimately, drying and storing sunflowers is a balancing act. “We get paid on how many pounds we deliver, whether it’s oil or sunflower seeds. The goal is to have it dry enough to store, but not too dry so that we start losing value in what we’re delivering to market,” says Hellevang.