Q & A
Grinding Mills
Answered by: Richard Alan Miller
Question from: Kathy Hedegard
Posted on: October 29, 1998

I’m looking for grinders suitable for grinding dried echinacea root. Do you know where I might find something like this?

There are several technologies used in the grinding of roots and barks, predicated on the final product. If you are using the root to make capsules or tablets, then you want a powder-type mill. The most preferred Powder Mill is a Micropul III, using a twin-stirrup type of swinging hammer. This is a hammer-mill type process, where two swinging hammers are connected by a bar across them.

What this does is cause the hammers to hit the product, causing it to powder quickly. Because the hammer is not rigid, the swinging action causes the hammer to hit the product harder. By connecting two hammers, this swinging action causes further particles to be caught in the action of the hammer and also increases the momentum of the hammer. This makes the powdering much more efficient.

There are a number of other Mills used for powdering, including Bell, Fitz, and Grundler. If the root is to be used for a food or drug, the inner milling chamber should also be made from stainless steel. Used machinery of this kind is easily found in most of the larger used machinery equipment houses like Arron (Chicago), Clark (Huntington Beach), or the numerous ones around New Jersey. Ads can be found in "Chemical Marketing New" and related chemical industry tabloids.

The other form of milling technology is called a shear-type mill. This principle uses a knife-edge across a dye-plate. Most shear mills have two dye edges and two or three knives on the rotor. What this does is gives less spread in particles sizes when the product is being cut. This reduces losses, especially when a C/S is required and smaller particles are not desired.

I found that the Nelmor was superior for breakdown and cleaning after a small job, because it breaks apart at the screen location. Fitz and other rigid hammer-type mills give a larger spread in particles sizes, often making them more suitable for use as a pre-milling operation for eventual powdering.

Of course, the speed at which the mill is fed, the screens used, and other factors all form a complex on the quality and efficiency of use in the final product. This is why I titled the chapter on milling in my book The Potential of Herbs As A Cash Crop as "The Art of Milling." When all is said and done, the quality of the final product is a result of the individual "artist" running the equipment.

All milled products, wether they were reduced to a smaller size or turned into powders must all be then sifted for uniform sizing. Powders vary on "over/under" sizing, depending on their specific gravity and eventual use. Tableting requires are larger sizing, usually in the 20-mesh USS, while capsulating is much smaller, starting in the 60-mesh USS.

A 20-mesh size means there are 20 particles per inch. Echniacea might require a specification of "all particles must be under 20-mesh, and over 40-mesh." Lighter items might require a 16/30-mesh USS as the way their sizing might be described. Obviously, anything larger needs to be remilled, and anything smaller is considered losses or used for capsulating.

This is why the selection of the specific type of mill, the screens used, and the actual operator who does the milling is critical. All these factors determine whether the end results are profitable - or not. Milling itself should be run as a separate business, with it’s own profit and loss statements over the growing and farming of the crop.

I strongly recommend a more detailed review of that chapter, and then reading my paper titled "A Centralized Processing Facility for Botanical Alternatives" for a better understanding of what options are available in this type of processing. I probably should eventually write a more detailed book on this subject, especially since my last name is "Miller." ha ha

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