Modern Methods of Milling
Milling great flour is not simply about crushing the grains into a powder. It is about separating the parts of a “berry” of grain into its constituent fractions. The best way to do this is through a shearing action where the white endosperm is literally scraped or sheared off the harder more fibrous bran.
Stone Grinding
From the history of Milling section it is quite clear that the process of using stones to grind wheat into flour is very old. The basic principle of a fixed “bed” stone and a rotating ”runner” stone has changed little in 1000s of years. The Runner stone has an eye in the centre through which a controlled stream of grain is poured and the milled meal or flour travels out to the edge of the stones along grooves or furrows.
At Shipton Mill we have pairs of stones that are used to produce a range of organic stoneground wholemeal flours. The secret is in the care of the stones, the setting of the stones during the milling process, the type of stone used and the “dressing” of the stones to keep them in the best condition for milling.
The stone itself is made from French Burr Stone, a type of very heavy marble that is hardwearing but at the same time has excellent heat transference properties. It is important that the heat is transferred away from the flour so that it is lightly warmed rather than toasted, as too much heat will cause excessive damage to the starch and reduce its baking qualities. The surfaces of the stones are cut so as to provide raised grooves or “lands” and recessed furrows, so that as the flour is milled it travels out along the furrows to the edge of the stones.
For a miller, it is important that the stones are kept in just the right profile and that the gap between the stones is as accurate as possible. Too big a gap or unbalanced stones will result in coarse or poorly ground flour which will deliver poor results in baking and fetch a reduced price. It was the task of the “Millwright”, typically a traveling craftsman, to correctly “dress” the stones using a “mill bill” or large beak shaped hammer with which the stones were carefully chipped away to ensure that they meshed together at just the right setting and rotated evenly and in a balanced manner.
A millwright’s experience would be determined by the Miller asking to be shown the “metal” he was made of, at which point the millwright would roll up his sleeves to reveal forearms studded with black specs – chips of stone and metal from the awl that fly off and embed in the forearm; the more extensive the forearm speckling the more experienced the millwright. Now modern techniques can be used to ensure that the stones are dressed properly and there are very few if any qualified traveling millwrights left.
Being a slower and more timely process, much of the natural goodness of the starting grain is left intact and stone ground flour is prized for its nutritional integrity. More modern milling techniques such as roller grinding does more damage to the starches, vitamins and minerals within the grain. Whilst the starch damage is often an added benefit in the baking of bread, the loss of the other constituents can off set the benefits and result in some needing to be added back in to the flour.
Roller Milling
As populations grew and the demand for more and better flour and bread grew, so a new milling process was devised. Originating in Hungary in the late 1870’s, this new process involved passing the grain between sets of spinning metal rollers or “rolls”. Initially the first roller mills were just using this process to break up the grain before then finishing the process between traditional stones.
Gradually the process was refined so a succession of rollers could be used to remove all the bran and wheat germ from the grain through a staged milling process or "reduction" with each consecutive set of rolls making the flour finer. The first set of rolls in a mill are called a “break” or "break rolls" and subsequent rolls are referred to as reductions rolls. By increasing the number of rolls and with other advances in milling technology affording better separation techniques, almost all the bran could be separated out to produce superfine white flour. The rcomplex system of breaks with fluted rollers and then a series of coarse to fine graded reduction rolls shear off the white endosperm from the bran and gradually reduce the particle size.
The first “break” splits the berry in to 2 or 3 parts and starts the shearing process, removing the white endosperm from the bran. The “middlings” are “bolted” or sieved to remove the bran. The middlings are then reground at the second and subsequent breaks using a slower grinding speed followed by more sieving and so on. To produce wholemeal flour from this type of milling it is necessary to collect all the “brown” particles that have been removed during the sieving processes and add them back to the final product. A "brown" flour is one where only a certain proportion and type of the extracted material is added back.
So not only are roller mills faster, they produce more white flour of a higher quality than was ever able to be extracted from stone milling and sieving. However because of their higher speeds and more vigorous action there is a lot more damage done to the components of the flour. There are ways to reduce the damage and maintain a greater level of natural nutrients and milling technology is evolving to reduce the pressures and temperatures within the rolls.