Several factors play in to producing quality durum

By SUE ROESLER, Farm & Ranch Guide
Sunday, March 2, 2008 10:08 AM CST

Brian Sorenson, NCI director, shows a slide of durum’s translucent vitreous kernel.

WILLISTON, N.D. - Sometimes durum producers feel they don't get the premium they deserve on their crop. A new automated grain analysis machine could help improve that situation.

Brian Sorenson, director of the Northern Crops Institute in Fargo, N.D., says the new Acurum from DuPont will be a boost to durum producers.

The Acurum, an automated grain analysis machine, uses digital imaging and artificial intelligence to objectively assess specific quality factors in grain, he said.

“It has been proven to be more consistent than grain inspectors,” Sorenson told durum producers at the National Hard Spring Wheat Show in Williston. “We're moving in the right direction with the Acurum.”

One of the most important factors in quality durum is a vitreous kernel, and 75 percent of vitreous is hard amber durum, said Sorenson. The vitreous part of the kernel usually appears glass-like and translucent, with a smooth interior and bright yellow color.

Sorenson showed a slide of durum kernels placed on a light box.

“See how impressive that is?” he said to producers. The kernels had a bright yellow see-through glow. “The light passes right through the kernel because it is so translucent. This is what's important for durum breeders.”

When the kernel is cut, the opaque part of the kernel is the chalky, starchy part.

Before the Acurum, inspectors would look at the kernels and determine the vitreous kernel percentage based on appearance.

That isn't always accurate, Sorenson.

Sometimes kernels have been bleached, but that doesn't mean they have a low percentage of vitreous, he explained. A non-vitreous kernel looks a lot like a bleached kernel.

“Inspectors don't have a lot of time to cut kernels and check for sure,” he added.

Inspectors may say the kernel is a high percentage of vitreous and it really wasn't, or they may say it has a low percentage of vitreous and be wrong.

“If the error works to your advantage, that's good. But if it doesn't, that's not so good,” Sorenson said.

The Acurum, which looks at the different wavelengths of light, was developed in Canada and has also been used in Australia and France. Recently, North Dakota has received three units, with one at the Dakota Growers Cooperatie in Carrington, he added.

A test done with the unit using 101 samples showed the Acurum is consistently more accurate than the inspectors.

The Acurum is fast, taking 1.5 minutes to examine 100 grams of durum.

“It does not slow down grain merchandising,” Sorenson said.

Cost is high, however, at $15,000- $25,000 per unit.

Currently, units examine the vitreous percentage, but it is being developed to examine other durum quality traits as well, he said.

Durum quality factors are important for producers because export markets often demand a high quality durum. North Africa and Europe both want high quality protein, a bright yellow color, and al dente texture, Sorenson said.

Export markets need high quality for cous cous and high protein is needed for durum bread, he added.

Semolina extraction is an important factor in the kernel. Not enough semolina leads to more flour which is not as desirable for pasta products.

“That's why there's a premium for choice milling durum,” he said. “For millers, high semolina is their highest value product.”

Wet gluten content is important as a measure of gluten mass that relates to the mixing and baking process, he said. It is related to the total crude protein content for hard red wheat. Hardness results in a strong protein matrix, he said.

“Gluten is responsible for mechanical strength, the pasta cooking quality and firmness,” he added.

Asia wants a softer noodle with low protein.

Many of the new varieties of new durum will have a higher gluten strength.

Some of the things that play into durum quality include dockage and foreign material, mycotoxins, pesticide residue, test weights, specks, shrinkage of kernels, and falling numbers.

“Falling numbers are an indication of preharvest sprouting damage,” Sorenson said. Lower falling numbers affect cooked pasta, making it have a softer texture. “It has been a few years since we've had a sprouting problem. Visible sprouting damage is considered the same as damaged kernels by the FGIS (Federal Grain Inspection Service).”

Sprouting in grain happens once the kernel has reached maturity if the wheat is subjected to proper moisture levels, temperature and time.

Moisture levels in the wheat can decrease prior to threshing, and stop the sprouting. If the sprouting stops before there are visible signs of sprouted kernels, it is known as incipient sprouting.

The impact of sprouting on pasta produced from durum depends on the amount of enzymes present and breakdown of the kernel. Sprouting lowers test weight and flour yield which lowers the grade and value to the miller.

Falling numbers, however, are not a FGIS grading factor, but are used for marketing.

Japan's minimum falling number is greater than 300 seconds.

Sorenson said sound wheat is considered to have a greater than 300 seconds falling number, while there is some sprouting at 200 to 300 seconds. Wheat is considered highly sprouted at 62 to 200 seconds. Pure water is considered equal to 62 seconds.

He said in the eastern part of the state, a variety of durum was found to have a falling number of less than 155. But it was later found that too much precipitation affected the falling number and when it was drier, that variety had a 250 falling number.

Japan is also a market that does not want any pesticide residue in its durum. They use a test for 200 pesticides and absolutely reject paraquat.

“They have never found paraquat in our wheat,” Sorenson said.

The 1,000 kernel weight is used in place of test weights in international markets, and is an indication of milling quality.

“Lower kernel test weight increase the cooking loss of pasta leading to a softer cooked pasta, stickier pasta,” he said.

Kernel size distribution may also be important to some millers and this test gives an indication of the range of kernel size in the unit.

“We had a large number of small kernels in our durum last year. A range of sizes causes problems for millers,” Sorenson.

Frank Mathey, NDSU durum quality specialist, talked about durum varieties that had specific qualities.

He said high ranking varieties for pasta color at Langdon were Dilse, Maier, Munich, Pierce and Alkabo. At Minot, high-ranking color varieties were Munich, Maier, Grenora, Divide and Pierce. At Williston, those varieties were Navigator (very high), Grenora, Munich, Dilse, Maier and Pierce.

However, it was found that high-ranking varieties for pasta color can turn out to have a poor color, he said.

The same was found to be true of varieties high in protein content and those high in gluten index.

What was found was that in undesirable environments, good varieties don't perform as well as if they were grown in an excellent environment.

It was also found that the same variety will perform differently in different locations. For example, Grenora ranked high for protein content at Langdon, but ranked low in protein when grown in Williston (six to nine year average).

Mathey concluded that top varieties differ with location; top varieties can have poor quality in undesirable environments; excellent environments do not compensate for inferior genetics; and top varieties for pasta quality may not be best for some agronomic qualities. 

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