Screen change agreed to in principle for wheat

Press, 21 October 1983, Page 26

Screen change agreed to in principle for wheat

The Wheat board has agreed in principle to change the standard screen used to separate broken, immature or shrivelled grain. This follows the publication of extensive testing on the screenings from Oroua wheat.

Mr Peter Cressey, of the Wheat Research Institute, told the recent Cereal Science Conference in Christchurch that some wheatgrowers were being penalised by the present screen — called the 5%A screen.

About 30 per cent of the material being screened from lines of Oroua was good quality, sound grain, he said.

Mr Cressey said that most other grain growing countries use a sieve with smaller holes — called a 5A sieve.

Mr Cressey said that use of the larger sieve in New Zealand (a slot size of 2.18 mm versus 1.98 mm elsewhere) seemed to be a result of the traditional breeding programme, which was geared to the production of large-grained wheats. “It was believed that a large grain contained more endosperm and gave better flour yields,” he said.

“However this is rather questionable and recently we have seen the release of two small-grained wheats, Oroua and Tiritea.

“Oroua now comprises 19 per cent of the total harvest and was the best breadbaking wheat over the last two years harvests. “It seems likely that the success of Oroua will lead to the release of more small-grained, high-quality cultivars, so we must consider whether the s¥zA sieve is a fair means of screening or is giving an unfair bias against improved quality cultivars.” He compared the effect of the two sieves on two cultivars, Oroua and Rongotea. Twenty-one lines grown in the Ashburton district were tested.

All samples were put through both sieves and a wide range of quality tests. He was particularly interested in grain which would be rejected by the 5%A sieve, but retained by the finer, 5A sieve.

“The statistical analysis showed that there was no significant difference between the two sets of results (either with the s¥zA or the 5A sieves) with respect to flour extraction, mechanical dough develop-

ment, work input, bake score and falling numbers. These are the factors which determine suitability and profitability of a wheat sample for milling and baking. “There are significant differences in kernel weight, colour grade and protein, but this is due to more rigorous testing rather than to any physically observable differences.”

But the fraction passed by one sieve and retained by the other gave some very interesting results.

“Kernel weights were in the range usually associated with the severely shrivelled samples, but other measures were not in line with this.

“Flour extraction rates were not very different from the bulk samples for the two sieves, though the grain content was higher.

“Protein content and falling numbers were about the same, or slightly higher than for the bulk samples.” The most unexpected results came from baking. “Work inputs, a factor of economic importance to the baker, appear lower. In practice this would result in lower energy requirements in the commercial plant,” said Mr Cressey.

“Baking quality, however, is much higher, to the extent of five or six points, which is highly significant on the Wheat Research Institute’s test baking system.

“These results seem to indicate that the standard* s¥zA screen doesn’t merely remove broken, immature and shrivelled grain, but also removes small grains capable of yielding over 70 per cent of flour, highly acceptable protein levels and falling numbers, and baking quality superior to the bulk sample.

“If cultivars such as Oroua are to play an increasing role in the wheat industry it seems some review of these screening methods may be necessary,” he said.

Following the conference the general manager of the Wheat Board, Mr Guy Elliott, said that the board had accepted in principle the need for a change in the screen.

It would now be necessary for the Wheat Research Institute to report fully on the ramifications of a change to a finer screen.

In particular the implications for the maximum screenings level for a wheat to be accepted for milling

grade would need to be examined. At present if the weight of screenings exceeds 3 per cent of the total weight this excess is deducted from the total weight when the price is calculated.

So for a screening level of 4 per cent the price is based on 99 per cent of the total weight of the wheat.

If the screening level is above 5 per cent the line is no longer considered to be up to milling standard and its acceptance by the buyer is a matter for negotiation.

So as Mr Elliott explained, it was not so much a matter of the Cressey research findings as regards Oroua as the effect a change in screen would have on the whole regulations which wold have to be examined further.

He could not say whether the necessary work could be complete to enable a change for next harvest. It might be 1985 before such a change could be made. Also perhaps not enough 5A screens would be available for the start of the next harvest, he said.

The director of the Wheat Research Institute, Mr T. A. Mitchell, said comparisons between the use of the two screens had been completed and the findings would be ented in a report to the t Board for its November meeting. If a change of screen was decided upon by the board, the wheat regulations would have to be amended.