Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
LOW BEVERAGE SOLUBLE IRON CONTENT
_ILTER AID AN~ METHOD FOR ITS PRODUCTION
Background of the Inventior,
The invention herein relates to filter aids, especially
diatomite, having a low soluble iron content. It also relates to a
method for production of such low soluble iron filter aid.
In the manufacture or processing of a number of vegetable
based beverages (notably beer, ale, wine and fruit juices) the
beverage is filtered one or more times through granular heterogeneous
filter media, usually diatomite. These filter media contain small
lo amounts of various minerals and compounds, among which are iron
compounds. A certain small portion of the iron content of the
media is soluble in the vegetable beverages. This portion of the
iron may be referred to as "beverage soluble iron" (often abbreviated
"BSI").
The presence of higher levels of BSI dissolved in the
beverage can be deleterious to the taste and long term stability
("shelf life") of the beverage. Consequently, it would be desirable
to have a filter medium which is low in BSI content but which
retains its desirable filtration and clarification properties.
Brief Summary of the Invention
The invention hereln is a method for the production of
low beverage soluble iron content filter aid, especially diatomite,
which comprises contacting granular filter aid containing an
initial content of beverage soluble iron with an aqueous solution
of tannic acid, gallic acid or mixtures thereof to reduce that
beverage soluble iron content. Color control agents such as citric
acid may also be present in the solution. Also a part of the
present invention is a filter aid low in beverage soluble iron
content produced in accordance with this method.
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Detailed Description and Preferred Embodiments
The basic material used in the process of the invention
is a granular filter aid which initially contains bevera~e soluble
iron. ("Initially" herein refers to the BSI content immediately
prior to the treating process of this invention. The filter aid by
that time will probably have already undergone prior processing
which may have altered the BSI content of the original material
such as crude ore froM which the filter aid is made.) For con-
venience, the invention herein will be discussed in terms oF
diatomite, since this is the common and preferred filter aid ~or -~
vegetable beverages. However, it will be understood that the -;~
process is also applicable to other filter aids, such as perlite
and clays, which contain beverage soluble iron. The considerations
discussed below for diatomite will be similarly applicable to these
other filter aids.
Diatomite is a naturally occurring material found in
deposits in various parts of the world. It is formed by the
deposition over many years of the si1iceous skeletons oF ancient
microscopic marine organisms known as diatoms. Commercial deposits
are found in California, Oregon, Washington and several other
states, as well as in several Foreign countries. The chemical
composition oF a typical diatomite is 85 to 30% silica, 2 to 4%
alumina, l to 2% ferric oxide, and small amounts (less than 1%) of
materials such as magnesia, lime, alkalies and titania. There are
also typically up to about 5% volatile materials including water,
carbon dioxide and organics.
After being minedg the diatomite (which is also frequently
known as "diatomaceous earth") may be crushed, screeneds calcined
and classified to separate it into a variety oF gracles of dif-ferent
granular sizes, purities and reactivities. The grade o-F diatomite
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1 and the various conventional steps of handling and processing are
not particularly critical to the present invention. The presence
of beverage so'iuble iron is in part a function of the chemical
composition of the original ore. The type of conventional (largely
mechanical and thermal) processing techniques used to produce the
commercial grades of diatomite may eFfect the overall amount of BSI
in the final diatomite product. ~lowever, this invention is generally
applicable to all varieties of diatomite containing significant
quantities of beverage soluble iron.
In the process of the present invention the beverage
soluble iron content of the diatomite is reduced by contacting the
granulated diatomite with an aqueous solution of tannic acid,
gallic acid or mixtures oF these acids. Tannic acid (also known as
gallotannic acid and tannin), is a natura'lly occurring substance
Found wide'ly in plants, particularly oak and sumac. The exact
molecular formula is unknown but is believed to be a mixture of a
number of gallic acid derivatives. A typical pub'lished formula is
C76H52046 with a molecular structure of
~1~20R
~ - o~OR
P~O~
oR
wherein R is galloyl, m-digalloyl, or m-trigalloyl substituents.
Typical commercial physical properties of tannic acid are that it
decomposes at about 210C; may be in the form of powder, flakes or
a spongy mass; is odorless; has a strong astringent taste3 and is
soluble in water, alcohol and acetone and almost insoluble in i
benzene, chloroform and ether.
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l Gallic acid (3,~,5-trihydroxybenzoic acid) is commonly in
the form of colorless or slightly yellow crystalline needles or
prisms which are soluble in alcohol and glycerol and sparingly
soluble in water and ether. It has a specific gravity of 1.7 and a
melting point of approximately 230C. It is commonly produced by
the action of mold on solutions of tannin or by boiling tannin with
strong acid or caustic soda.
In the present invention the diatomite is treated by
contacting with aqueous solutions of tannic acid, gallic acid or
mixtures of these two. The solution will normally contain 1~ to
20% acid by weight although the strength oF the acid solution is
not critical. The amount of acid (measured as acid rather than
solution) useful in the present process will be in the range of
From 0.1 to 1.5 grn-moles of acid per ton of diatomite, preferable
0.2 to 1.2 gm-moles of acid per ton of diatomite.
Contacting may be accomplished by any o~ several means.
The acid solution may be sprayed on the diatomite while the latter
is being classified by suspension in an air stream. Alternatively,
the diatomite may be simply washed with the acid, as for instance
being put through a bath of the acid solution, or having the acid
poured through a layer of the diatomite. Other conventional
liquid/solid contacting means such as fluidized beds may also be
used. The particular choice of technique to contact the acid and
diatomite will often be based on availab1e equipment, economics and
similar criteria.
The time of contact will vary according to the strength
of the acid solution and the amount of beverage soluble iron
present in the diatomite (a typical analysis of diatomite shows 45
to 55 ppm of BSI). The contact time may be very short, such as
merely the time it takes to form a slurry of the diatomite in the
1 solution and filter it. The optimum treating time For any specific
sample of diatomite and strength of acid can be readily determined
by routine experimentation.
If desired, the diatomite and/or acid solution may also
be heated to a temperature on the order of 90C to 100C prior to
contacting to expedite the reaction by which the acid extracts ~SI
from the diatomite. The exact nature of this extraction reaction
is not known, but it is believed that the iron is extracted by
being complexed with the acid.
lo Following the acid contacting the diatomite may be
washed with water to remove the acid and extracted iron. If
desired, a plurality of rinses may be used, the rinse water may be
heated, and/or varying lengths of rinse period may be used.
However, rinsing is not mandatory, for after being treated with the
acid the iron solubility in the beverages is reduced whether it
remains on the diatomite or is removed by rinsing. The optimum
rinse techniques, if any, will be a simple matter of choice for one -
skilled in the art.
If desired, the aqueous solution of tannic and/or gallic
acid may also contain color control agents. These acids have a
tendency to impart dark color to solutions~ and the color control
agents react with any excess acid to reduce that tendency9 thus
discolorizing the solutions. Suitable color control agents include
citric acid, sodium sulfite, potassium bromate, and ethylene diamine
tetraacetric acid. Levels of concentration of these agents will be
a matter of routine choice, but typical levels which have been
found satisfactory are 0.2 to 0.3 molar in a solution which is 0.04
molar in tannic and/or gallic acid.
The following examples will illustrate the process of
this invention. 50 gm samples of a flux calcined California
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1 diatomite containing approximately 45 to 55 ppm BSI was pre-heated
to approximately 200F (93C) for three hours. Aqueous solutions
of acid were made up using 17% acid in water. Each sample of
heated diatomite was put into a blender which was equipped with
heating means for maintaining the preheat temperature. Agitation
of the diatomite to form an air suspension was obtained by the
blender blades. The acid was sprayed into the blender jar.
Complete dispersion of the acid through the diatomite was obtained
in appro~imately 2 minutes. The diatomite was then dried and the
BSI concentration determined.
In an alternative technique a filter cake was formed on a
Buchner filter using 50 gm of diatomite and water. The ~ilter cake
was then washed with 500 ml of 17% acid solution. The acid remained
in contact with the filter cake for approximately 10 minutes.
Thereafter the filter cake was rinsed with water, dried, and BSI
concentration determined. Results were found to be equivalent to
the spray technique.
Typical results are presented in the table below.
Dosage Reduction
lb acid/ton diatomite of BSI, %
Tannic Acid 0.9 30
1.7 50
1.8 35
1,9 53
3.3 70
3.6 68
Gallic Acid 0.43 7
0.85 35
0.95 12
1.9 30
2.9 40
It will be evident from these data that the process of
the present invention significantly reduces the amount of beverage
soluble iron present in diatomite filtrates. The resultant low
beverage soluble iron content diatomite therefore makes a superior
filtration medium for vegetable beverages for it substantially
reduces the amount of iron which is extracted by the beverage from
the diatomite during filtration.
Other contacting fluids were experimented with to determine
if there were other materials equivalent to tannic and gallic
acids. Water, starch, sucrose, monobasic sodium phosphate, tartaric
acid, gluconic acid, sallcyllc acid, and the sodium salt of ethylene
diamine tetraacetic acid were all tried. The organic acids in this
group produced only insignificant reduction in BSI. The remaining
materials were able to reduce BSI by larger amounts than the
organic acids, but took long time periods ~often 10 days to 2
weeks) to reach the BSI reduction levels obtained with tannic and
gallic acids in a matter of minutes.
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