Water and Flour Don't Mix
The moisture content of the wheat is very important as it plays a significant role in the efficient removal of the outer layer of bran thus leaving the endosperm to be milled into very clean white flour. Wheat grown in different locations or even the same location but with different farming and irrigating methods, and timing of harvest, will have widely varying moisture levels and milling properties.
Grain that is too moist will become mouldy and rot.
Depending on where the wheat is grown and how it is grown and when it is harvested, atmospheric conditions and the type of milling machinery used, the wheat may be “misted” with water vapour in order to increase its moisture to facilitate the milling process. This process is known as conditioning or tempering. The Talmud (Pesachim 40a) calls it "Lessisa"; Rava rules that it is a Mitzva to soak the grain prior to milling it because it makes a superior tastier product.
Converting Wheat to Flour
Wheat is milled between two large metal rollers known as breaker rolls. These rollers rotate in opposing directions. They are grooved in order to grip the wheat seed and hold it. If everything goes to plan the outer husk is removed in a couple of large pieces rather than being crushed into many small pieces. This makes the task of obtaining fine white clean flour, much easier.
The clean course crush is then sorted into various grades with the endosperm being crushed between smooth flat rollers. On average, 20,000 grains of flour will be produced from every single wheat grain.
It is well known that very finely divided material, such as flour, poses a risk of explosion. (The solid booster rockets for space launchers are comprised of very finely divided aluminium) This is so because the proportion of exposed area is very large when compared to the mass of the material. When exposed to oxygen there will be a chemical reaction which is exothermic i.e. which produces heat. As the product warms, it oxidises more rapidly. This is an ongoing and accelerating reaction which leads to explosion. There seems to be a myth that these risks require that water be sprayed upon the wheat during its processing. This is untrue. Water, even in the tiniest amounts, would interfere in the worst possible way with the manufacturing process by gumming up the system. The flour would turn into “Clag”.
Matza requires vigilance from its earliest point. We will begin with producing the flour for Matza.
1) Wheat is received at the flour mill and inspected. Samples of wheat are taken for physical and chemical analysis. The wheat is graded based on several factors, the most important of which is the protein content. The wheat is stored in silos until milling.
2) Before wheat is ground into flour it must be free of foreign matter. This requires several different cleaning processes.
a. In a device known as a separator the wheat passes over a series of metal screens to remove large objects such as sticks and stones.
b. The aspirator works like a vacuum cleaner, sucking away foreign matter which is lighter than the wheat.
c. The disk separator moves the wheat over a series of disks with indentations that collect the grains of wheat whereas smaller and larger objects pass over the disks.
d. The spiral seed separator takes advantage of the oval shape of wheat grains. As the grains move down a rapidly spinning cylinder the oval wheat grains gravitate toward the centre of the cylinder while the round seeds move to the sides of the cylinder.
e. Magnets remove small pieces of metal; scourers scrape off dirt and hair, and electronic “eyes” remove material which is not the same colour as healthy wheat.