(You never know where you can get your processing equipment marketing articles published but it's always fun when it's a high end consumer market publication like ARTISAN SPIRIT MAGAZINE. This article was just published in the Winter issue. Look for it in your mailbox, we'll be sending copies to our clients and prospects. It was also published in Feb 2016 PROCESSING Magazine.)
Photo "Grain" by Amanda Joy Christensen of Artisan Spirit Magazine
Article By Eric Marcotte, Stedman Machine Company, Inside Sales Manager
Archeologists and historians have debated the early origins of alcoholic beverages with evidence of wine grapes dating back 10,000 years. Alcoholic beverages were desirable as potable liquid for travel. Some believe wine came first, eventually followed by an accidental mash up of grain and water that yielded beer. But distilled spirits are definitely in the mix – and the milling. The Old Bushmills Distillery in Northern Ireland is the oldest licensed whiskey distillery in the world, with its license issued in 1608.
So what’s changed over time? In a word – efficiency. The steps necessary to convert raw grains into the myriad of beverages millions enjoy today remain largely the same. However, the processes have been refined or streamlined and are now considerably more efficient.
Let’s take stock of the steps to produce these whiskeys beginning with milling. Milling breaks up cereal grains so that water can penetrate and facilitate the cooking process. Grinding grains is the process of increasing surface area. More surface area gives water and enzymes a better opportunity to penetrate the grain. A particle 1 inch in diameter has a total surface area of 6 square inches. If you divide one particle into 1,000 particles, surface area becomes 6,000 square inches.
The optimal size of the ground material varies according to the master distiller, but the science behind the opinions includes making particles so fine that they allow maximum access for hydrolysis of starch. Another school of thought proposes larger particles are the way to go for better yield. Whether fine or coarse, the idea is to expose the starch to water in a way that won’t cause handling problems. If the mash is too hard to de-water then, the distiller may lose liquid containing alcohol, decreasing yield.
Particle size distribution analysis of the meal should be done on a regular basis. When the distribution falls outside specifications, the mill should be adjusted.
TYPES OF MILLING MACHINES
Grinding of corn, rye and malted barley in distilled liquor production calls for equipment performance typically required in food plants. The grain must not be overheated in the grinding process, as this could affect the final product flavor. And the ground grain must be uniform, relatively coarse and contain as little flour, or dust, as possible to prevent handling and dewatering problems.
Generally a hammer mill is used for corn, wheat and rye; a roller mill for malted barley; and a cage mill can be used for all four.
Hammer mills use rectangular pieces of hardened steel attached to a shaft rotating at a high speed inside the milling chamber. The rotating “hammers” accelerate the grain into breaker plates lining the housing of the mill. Next, the grain encounters a changeable screen with a “close tolerance” gap between it and the rotating hammers. A unique characteristic of hammer mill grinding is that material must pass through the screen to exit the mill. This guarantees the final product maximum size. Hammer configuration, rotation speed and screen sizes can be varied to process different grains. Each component can be changed individually. More hammers, faster speeds, and finer screens produce a finer grind.
Hammer mills eliminate the need to screen product. When you fine-grind with a hammer mill, it may take more power per ton and maintenance costs may be higher compared to roller mills. The possibility of overgrinding, creating too many fines – is also something the master distiller should consider when using a hammer mill.
Roller mills use compression to reduce the size of the grain as it passes between stacked pairs of rollers. The smooth rolls may turn at different speeds to introduce shearing forces, and the addition of grooved rolls adds tearing and grinding to the milling actions. Their slow speed doesn’t cause heating of the grain or related moisture loss. Small amounts of fine materials are produced, keeping dust down. The shape of the particle produced is irregular, cubical and spherical so the grain doesn’t tend to pack or become a solid mass. Bulk density is about 10-percent less than grain milled by a hammer mill, as the ground material is coarser.
Roller mills may have a larger capital cost but use less horsepower per ton. Corn is an abrasive grain and may wear out a roller mill. Rollers mills may require screening to get a specific grain size distribution.
The cage mill consists of one or more rotating cages enclosed in a steel housing. Material to be ground is fed into the center of the revolving inner cage and passes outward via centrifugal force from row-to-row, finally discharging through the bottom of the mill. The source of size reduction in a cage mill is the result of impaction between the material being fed and the pins of the revolving cages. Impact-type grinding in the cage mill does not cause excessive heat and produces a uniform grind with minimum flour. Cage mills are used for larger production batches or continuous operations and can be used for corn, wheat rye, malted barley and many other grains.
Properly setting the speed of the cages allows the succeeding rows, moving from the innermost outward, to act principally on the particles that have not yet been reduced to the desired size. Particles that have been crushed sufficiently tend to pass through the subsequent rows without being materially affected. Thus over-crushing and under-crushing is effectively controlled by adjusting the speed of the cages.
The major difference with the cage mill compared to other size reduction methods is the absence of close clearances between the crushing parts leading to less maintenance. Also, they do not require grate bars or screens for final product sizing. Cage mills produce a cubical product of consistent particle size distribution, and there is no decrease in quality of the product even after long periods of operation.
MILLING AND ALCOHOL PRODUCTION PERCENTAGES
Fine versus coarse grind can cause a 5-to-10-percent difference in alcohol yield. An upper limit of about 20-percent alcohol is possible with a very fine grind, but the flavor may be altered. Also, finer grinds may be harder to press, and some yield may be lost.
There’s considerable available data on grinding for distillation. You’ll find the distilling community very helpful with advice for your situation. Part of the equipment choice may be the preference of the master distiller. Good milling equipment companies will help test your process on scalable equipment before purchase. The best equipment manufacturers also offer toll-processing services for batches large enough to improve your process or for experimentation with new ingredients and grind specifications.
Cheers to that!