Health Practices for the Operation of Historic Grist Mills
1. The production of a clean flour and meal product starts with the quality
and cleanliness of the grain purchased. The source of all grains should
be from a reliable grain company or from a commercial miller.
2. All grains used in the mill should meet the current Food and Drug Administration
standards for filth and extraneous matter. The use of grain from a local
farm source, including that which may have been grown on a demonstration
farm, is discouraged unless such grain has been cleaned by use of modern
equipment normally used by commercial millers.
Grains used in the grinding process are subject to contamination from birds,
rodents, stored product insects, and moisture. The degree of protection
the stored grain has against these contaminants will determine the period
of time for storage. The mill operator or mill manger of the grist mill
should consider the following questions:
1. Are storage bins (or other facilities) of mouse and rat resistant construction?
2. Are bins (or other facilities) constructed to prevent the entrance of
birds or the dropping of bird contaminants (feathers, feces, insects, or
other contaminants such as grease and oil) into the storage area?
3. Will the temperature of the storage area be below 70 degrees most of
the time during the storage period?
4. Is the storage facility free from overhead leakage?
5. Is the storage area free from flooding, excessive dampness or other moisture
conditions that will cause the grain to mildew?
In addition to contamination that may occur during storage, grains generally
contain the eggs of several kinds of insects. These eggs hatch during storage.
The length of time required for this to occur varies depending on the temperature
at which the grain is stored. Ambient storage temperatures below 60 degrees
will extend the time required for the eggs to hatch to several months. Temperatures
above 70 degrees will cause more rapid hatching of the eggs and shorten
the acceptable storage time. When the temperature is between 70 degrees
and 85 degrees, the hatching time is between 30 and 80 days.
Accordingly, grain storage periods during the colder months of the year
may be longer than during the warmer months. Good management of the mill
requires that length of storage be limited so as to afford maximum control
of the stored product. The quality of grain milled during any day or week
relates directly to the quantity of unprocessed grain required. Storage
of the grain must be closely controlled.
Grain Storage Facility
Two types of storage may be practiced, bulk or bin. Either of these types
of storage may be practiced, but the bulk storage of grain will usually
depend on the availability of supplies and the amount of grain processed.
In areas where a supplier is available within a reasonable distance, the
bulk storage of grain is not recommended. Remember, the smaller the quantities
of grain, the faster it moves and the less problem you will have with stored
Bin storage is the storage of cleaned grain in hoppers or bins that provide
a gravity feed to the grinding millstones. The quantity of grain in these
bins should be managed so storage time is kept to a minimum. Again, the
time period during which grain should be stored is determined by the temperature
The bins or bulk storage facility should be constructed to exclude rodents,
insects, and birds. It should also be constructed and located (especially
bulk storage facilities) to maintain the grain in a dry condition. While
cool temperatures will slow the hatching of insect eggs, storage in basements
or other below ground facilities is to be discouraged because of the possibility
of flooding or moisture seeping through exterior walls.
Storage bins and bulk storage facility should be cleanable. Cracks and crevices
in in wooden bins make cleaning difficult or impossible. Grain or grain
dust retained in these cracks and crevices for an extended storage period
may contribute significantly to the presence of insects and insect fragments
in the final product. Cracks and crevices should be filled with a caulking
material which is non-toxic to humans.
Bulk grain storage facilities should be completely emptied and thoroughly
cleaned after each lot of grain is used. New lots of grain should not be
added to previous supplies or a problem with stored product insects will
Grain storage areas should not be located in the basement and attic areas
since these areas contain the two prime ingredients for insect infestation,
heat and moisture.
Grain is usually delivered to the grist mill at ground level so it must
be lifted to bins or hoppers above the grinding millstones. Elevators are
usually used for this purpose. Their designs may vary but generally these
elevators are movable buckets attached to a continuous cloth belt. Grains
elevators at grist mills are usually used on a periodic basis to fill the
bins or hoppers. Following each use, the elevator should be thoroughly cleaned.
This cleaning can be best done with a bristled brush and a vacuum cleaner.
Thorough cleaning requires the buckets and belt to be rotated so all buckets
and conveyor to which they are attached can be cleaned. This also includes
all chutes attached to the system.
The bottom of the elevator shafts (the "boot") should also be
thoroughly cleaned with a bristle brush and vacuum. To do this will require
the removal of a portion of the shaft enclosure. If the elevator shaft or
boot does not have removable sections, the boot should be modified to permit
this cleaning. Also the legs of the elevator should be modified with removable
sections for better cleaning and attached with screws.
All inspection doors or windows in the elevator legs should also be cleaned
since these areas will trap material.
Even though cleaned grain has been purchased, it may be recommended that
the grain be cleaned before it is placed in the bin or hopper above the
millstones. This final cleaning of the grain before it is ground will help
maintain a good sanitary product. Historical type cleaners with shakers
or rotating screens, and fans can be effectively used when properly operated
As with elevators, cleaners should be used only on a periodic basis. After
each use, the cleaner screens and interior surfaces should be thoroughly
cleaned. A bristle brush and vacuum cleaner should be used. If the cleaner
does not have removable panels to permit cleaning of all interior surfaces
and screens, modification should be made to allow such cleaning.
Also, the material which passes through the screens should be removed after
each use of the cleaner and discarded to waster or hauled away from the
mill. If immediate removal is not possible, storage of this waste material
should be in metal containers with a tight fitting lid.
The area around the edges of the grinding stones should be cleaned by a
vacuum cleaner along with the millstone covers after each days operation.
Also clean the eye of the millstones including the driver and balance rynd.
During the colder months, lift the millstones once a week for cleaning with
a bristle brush and vacuum cleaner. During the warm months, clean between
the millstones each day of operation.
When starting to grind, discard to waster the initial flour discharged from
the millstones. The amount to be discarded will vary. Visually check the
ground product and when it appears free of foreign material, the flour or
meal may be discharged into the bin for later packaging. The bins should
have a tight fitting lid.
After the millstones have been dressed, they should be cleaned with a bristle
brush and vacuum cleaner, and then purged with 50 to 75 pounds of grain
to remove all stone chips. A brush and vacuum cleaner will not remove all
the stone chips. This material should then be discarded as waste before
product grinding can resume.
See section of elevators.
See section on grain cleaners.
Clean the flour bins or meal boxes after each day's operation. These bins
or boxes should be constructed so they are free of cracks and crevices.
Cleaning should be accomplished with a bristle brush and a vacuum cleaner.
When these bins or boxes have ground product in them, and the product is
not being bagged, their removable covers should be replaced. Visitors should
not be allowed to handle the ground product.
Package containers (cloth bags), scoops, scales, and a clean work surface
(table) are necessary. Containers used for packaging should be stored in
a clean dry place protected from dust, cobwebs, dirt, moisture, insects
and rodents. Scoops and paddles used to fill the package containers should
be clean, cleaned after each days use, and stored in a location free of
dust, dirt, insects, rodents, birds, and visitor contact. The scoops should
be constructed of non-toxic material, the product contact surfaces should
be smooth, and the handle should be plugged to prevent the accumulation
of flour or meal in it. The work surface (table or counter top) should be
constructed of a smooth cleanable surface preferably with a rounded edging.
If the surface is constructed of wood, the wood should be sealed and free
of cracks and crevices. If this surface is covered with a glass or plastic
cover it should be removable for cleaning between its surface and where
it makes contact with the table surface.
Storage of Meal or Flour
The insect eggs naturally occurring in grains will be carried through the
entire process. Therefore, storage times and temperatures are as important
for the finished product as they are with the grain. See section on grain
storage for these guidelines.
To help control the hatching of the stored product insects, the management
of the inventory of packaged flour and meal is important. The quantity should
be limited to the amount that can be sold or used during a specific time
period, and the inventory should be rotated on the "first in -first
out" principle. Dating packages of the finished product may also aid
in controlling the length of time any one package is kept. Mechanical refrigeration
that keeps the temperature of the ground product below 60 degrees will extend
the storage period. However, even under refrigerated conditions
the ground product at ambient temperatures should not exceed 10 days during
the winter months and 7 days during the summer. This is why freezing the
product immediately after packaging is most highly recommended.
The storage facility for the finished product should be located in a clean,
dry place and the cabinet should be screened or have solid sides to keep
rodents and insects out.
Flour and meal storage areas should not be located in the basement and attic
areas since these areas contain the two prime ingredients for insect infestation,
heat and moisture.
Floors, walls, ceiling, and windows should be kept clean and free of flour
or grain dust and cobwebs. Vacuuming the floors, walls, and ceilings at
established frequencies will maintain the mill in a clean condition. The
frequency will have to be determined by each mill operator because the amount
of flour and meal ground and the frequency it is ground will govern the
general cleaning requirements. In any event, it is suggested that general
cleaning be performed at least once a week.
Smoking in the mill should be prohibited.
No food, drink or other liquid or solid substances should be brought into
the mill by visitors. Visitors should be required to wear shirts and have
no bare feet. All visitors should be in a clean attire free from sweat,
dirt and grease or any material which could contaminate the mill, grains
or flour products. No pets should be allowed in the mill, with the exception
of the mill's cat which should be kept for rodent control. This would include
artists paints and thinners. Daily cleaning shall be conducted even when
the mill is not operating.
Dustless cleaning methods should be used. Vacuum cleaning is the method
of choice providing the dust bag is in good repair and is capable of retaining
the flour dust. Flour dust is more explosive than gun powder and 35 times
more explosive than coal dust. A sparkless vacuum motor is highly recommended
which is capable of vacuuming up flour dust, and all sizes of grain. A built
in vacuuming system is highly recommended which is hidden in a false bin
and elevator or chute, but use traditional inspection doors as access ports.
Empty all vacuum cleaners daily, and remove all waste material from the
mill at the end of each work day. No waste material should be stored in
the mill overnight.
Prior to general cleaning it is suggested that chutes, millstones surfaces,
and other enclosed area where vacuum cleaning is not practical be blown
free of grain dust.
Window washing should be done using a mixture of water and ammonia or one
of the commercially available window cleaners. Such cleaning should be done
at least once a year.
When flooding occurs in the mill wet cleaning with a mixture of water and
of commercial cleaners is necessary before grain grinding can resume, wash
all surfaces and utensils in the mill that have been effected by flood waters,
remove all contaminated grain and flour products immediately from the mill
No persons working in the milling operation should have an illness that
can be transmitted through the milled grains.
Persons working in the mill should wear clean outer garments and wash their
hands before handling the grain or ground products.
The construction characteristics of grain storage facilities, storage bins
or hoppers, flour bins, flooring, and work stations surfaces have been discussed
in previous sections. The exterior of the mill building should be of such
construction to resist the entrance of mice, rats, and birds. Where openings
to the exterior exist, these should be stopped or plugged so pests don't
have an easy access to the grain or finished products. A mill's cat should
be kept for rodent control and be trained not to jump onto tables, bins
millstone covers, etc.
Windows, doorways, and ventilation openings should be screened with standard
window screen material. Preferably such screening should be on the exterior
of the building to avoid a cleaning problem from flour dust. Also, the screening
of windows that may be opened should be removable to permit cleaning of
the glass area.
Operational doorways should be kept closed except when in use.
Chemicals to control pests should be used, if necessary, only when the exterior
of the building has been improved to discourage entry by pests. Chemicals
are at times the best, but only a temporary control measure.
When chemical control is found to be necessary, care should be exercised
in what chemicals are used, the amount used. Avoiding contamination of the
grain, process equipment, utensils, packaging materials, and the flour and
meal products is a must. Pesticides should be used according to label instruction.
Unless someone at the grist mill is specially trained in pest control and
particularly knowledgeable of pesticides, it is suggested that chemical
controls be purchased from a commercial pest control service or operator.
If chemical pesticides are stored in the mill they should be stored in appropriate
containers away from areas of grain and product storage.
When the pest problem is mouse or rat control, trapping is an effective
alternative to the use of chemicals or poisons. In addition, the staff at
the grist mill would be able to set and maintain all traps.
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