Milling Operations

This page explains the process of transforming wheat into flour - milling. A wheat grain consists of:

1) an outer protective coating (bran)
2) the plant embryo (wheat germ), which is the "baby" plant
3) the wheat germ's food store (endosperm).

Milling is the process of removing the bran and wheat germ to leave the endosperm. The endosperm is then ground or crushed into particles of a consistent size. The term milling is used broadly to describe the three main stages of making flour: preparation of the wheat, milling and blending.

Grain Preparation

The wheat is delivered by lorry and stored in a silo. It is then taken to the screenroom, where it is cleaned to remove impurities. Grain that does not meet specific requirements of a particular size, shape, gravity and air resistance are also removed.

The screened grain is then conditioned, which involves ensuring that the moisture within each grain is consistent throughout the grain and that the moisture throughout all the grain is consistent. The correct level of moistening is achieved using an automatic moisture measure and control system that takes into account the wheat's current moisture level and temperature. Moist grain makes the bran less brittle, so that it does not break into small pieces. Consequently, it separates more cleanly from the endosperm. The conditioned wheat is store in "conditioned wheat bins".

Batches of cleaned and conditioned wheat are then mixed together in a process called gristing. Gristing is done to create a flour whith the required qualities.

Milling

The conditioned wheat is then broken into fragments using a rollermill (breaking). The rollermill consists of two metal rollers separated by a small gap. The rollers spin at high speed, with one rolling faster than the other. The difference in rotation speed means that the wheat grain is ripped apart. Breaking produces fragments of bran, largely bran-free endosperm (semolina) and some flour.

The wheat fragments are then separated and refined through a series of sieves and reduction rollers. Sieving extracts the flour particles that are the desired size. The remaining larger particles are then reduced by passing them through smooth rollers up to 12 times. The fragments are sieved after each pass through the reduction rollers. This sieving and reduction separates the fragments into flour, bran, wheat germ and wheat feed. These separated products are called streams and there are several flour streams, the first sieving being the whitest and subsequent sievings producing browner streams.

Blending

Usually, the various flours, bran and germ produced during the milling process are then blended together to produce types of flour demanded by the customer. Wholemeal flours, for example are produced by blending back together the flour, bran and wheat germ. After blending, the flour is sieve again and packed into bulk packaging or bags.

PeriTec

Nelstrops uses the advanced PeriTec process in its milling operations. The PeriTec process sequentially removes the outer kernel bran layers prior to milling or subsequent processing, which optimises the yield and reduces the amount of bran contamination in the finished product.