Method of filtering edible liquids

The disclosed process provides for the treatment of edible cooking oils with a closed packet containing hydrated filtering material to absorb unwanted constituents.

The present invention relates to methods of filtering undesirable taste 
constituents from edible liquids. The present invention also relates to 
filter media for use in such methods and to filtering devices for carrying 
out such methods. 
BACKGROUND OF THE INVENTION 
There are many food processes which can benefit from the use of a filter 
for purifying, clarifying, improving, and reclaiming edible liquids. The 
present invention is applicable to all such processes, such as reclaiming 
cooking oil in restaurants, and clarifying and improving the taste of 
wine. 
Prior to the present invention, many restaurants have periodically passed 
the cooking oil used for deep fat frying through a porous pad in order to 
remove food particles. Such filtering, however, did not prevent the 
build-up of oil degradation products, like fatty acids, polymers, 
non-volatiles, volatiles and coloring bodies which adversely affect the 
taste and color of foods fried in such oil. Various efforts have been made 
to remove such acids and bodies from used cooking oil. U.S. Pat. No. 
4,330,565 entitled "FRYER OIL TREATMENT COMPOSITION AND METHOD" issued to 
Friedman on May 18, 1982, discloses use of a composition of water, a food 
compatible acid, such as citric acid, tartaric acid, acetic acid, 
phosphoric acid or malic acid, and a carrier containing rhyolite or 
perlite. The carrier of Friedman may also contain in addition to the 
rhyolite or perlite; activated carbon, fuller's earth, silica gel, 
bauxite, alumina, and diatomaceous earth. U.S. Pat. No. 4,112,129 of 
Duensing et al entitled "COOKING OIL TREATING SYSTEM AND COMPOSITION 
THEREFOR" dated Sept. 5, 1978, discloses a filter composition for the same 
purpose of diatomite, synthetic calcium silicate hydrate, and synthetic 
magnesium silicate hydrate. In these processes and the process of 
copending U.S. Pat. No. 4,764,384, of John Gyann filed Apr. 3, 1986, 
entitled FILTERING MEDIA AND METHOD OF USING SAME, under common assignment 
with the present application, granulated filtering material is added to 
hot cooking oil to absorb unwanted taste constituents therefrom, and 
thereafter the filtering media is mechanically filtered from the cooking 
oil, thereby rejuvenating the cooking oil. In the practice of such 
processes, the cooking oil is generally filtered through a layer of filter 
paper to remove solid particles of food which may be present in the 
cooking oil and to remove the filter media itself. A filtering aid is 
generally employed with the filtering media to facilitate the flow of the 
cooking oil through the media to the paper filter. 
Not all fast food restaurants utilize mechanical filter equipment to remove 
particles of food from the deep fat cooking oil. The processes disclosed 
above cannot be used in such fast food restaurants or require the addition 
of mechanical filtering equipment. It is an object of the present 
invention to provide a process for removing unwanted taste constituents 
from a liquid which does not require mechanical filtration equipment. 
In some fast food restaurants, filtering of the filter media from the 
cooking oil by a mechanical filter fails to remove all of the filter 
media. As a result, the cooking oil becomes contaminated by filter media, 
and the filter media represents an undesirable additive to the rejuvenated 
cooking oil. Faulty mechanical filtering equipment can result in this 
condition of the rejuvenated cooking oil. It is a further object of the 
present invention to provide a process for filtering edible liquids which 
significantly reduces the possibility of contamination of the edible 
liquid by the filter media. 
The filter media disclosed in U.S. Pat. No. 4,764,384 of John Gyann 
referred to above utilizes hydrated synthetic amorphous silica and 
synthetic amorphous magnesium silicate as its principal active agents, but 
a filter media limited to these active agents results in a slow mechanical 
filtration process. To increase the speed of filtration, a filtering aid 
is utilized, and the filter media disclosed in said patent application is 
diatomaceous earth, diatomaceous earth being selected because it also 
contributes to filtration. As a result, more filter media must be admixed 
with the cooking oil to produce satisfactory removal of unwanted taste 
constituents. 
Duensing U.S. Pat. No. 4,112,129 seeks to create adequate flow rates in a 
filter medium of diatomite, synthetic calcium silicate hydrate, and 
synthetic magnesium silicate hydrate by control of particle size, but the 
particle size requirement makes it necessary to use more coarse materials 
than are conventionally available. It is an object of the present 
invention to eliminate or reduce the need for a filter aid, or to select 
materials of unconventional particle size, in the filter media utilized to 
remove unwanted taste constituents from an edible liquid. 
The inventor has found that it is desirable to add some ingredient to the 
edible liquid, such as an antioxidant, which will remain in the liquid 
after treatment. It is a further object of the present invention to add 
ingredients to the edible liquid simultaneously with the filtration 
process. 
It is a further objection of the present invention to provide an improved 
filtering media for use with edible liquids, particularly such a filtering 
media which is particularly suited for use in packets according to the 
present invention. 
THE INVENTION 
The inventor has achieved the foregoing objects of the present invention by 
utilizing filter media in the form of a porous mass in packets, the 
packets having walls which are permeable to the edible liquid to be 
filtered and impermeable to the filter media disposed within the packet. 
The size of the packets is selected to limit the quantity of the filter 
media within the packet to a quantity which will permit all portions of 
the filter media in the packet to have good contact with the edible 
liquid. The packets have advantages over a mere mass of granulated filter 
material in filtering a flow of liquid to be filtered, but are 
particularly useful when immersed in a body of randomly circulating 
liquid, such as a heated vat of spent cooking oil, or a keg or glass of 
wine. It will be recognized that the use of packets permits the filter 
material to be removed in a relatively large body, and when used in a pool 
of liquid, by straining or ladeling. Since there is no predominant 
direction of flow for the liquid in a pool, the filter media is not forced 
against the walls of the packet to become closely packed and restrict flow 
as is the case with mechanical straining. 
The inventor utilizes a process in which a mass of granulated filtering 
material which takes up the unwanted constituents of an edible liquid is 
placed in a packet with walls sufficiently porous to permit the liquid to 
be filtered to freely pass through the walls, but the walls of the packet 
are impermeable with respect to the filter material. The packet is 
thereafter closed to retain the filtering material therein. Thereafter, 
the closed packet containing filtering material is placed in a body of the 
liquid to be filtered and maintained in the liquid for a period of time, 
such as 5 minutes. Preferably the liquid is agitated during this period of 
time, and may be under boiling conditions. As a result, the liquid 
penetrates the packet and the filter material within the packet, thereby 
permitting the unwanted constituents of the liquid to be taken up in the 
filtering material within the packet. After the period of time lapses, the 
packet is removed from the body of liquid, the liquid thus being 
conditioned or rejuvenated. 
The packet may also be utilized to add ingredients to the liquid being 
reconditioned or treated. In reconditioning spent cooking oil, it is 
desirable to add an antioxident to the oil, and the antioxident is 
preferably mixed with the filter media in the packet. 
The inventor has also provided a novel filter material for use in the 
packets. The filter material should provide sufficient porosity without 
the need for a filter aid, since the filter aid takes up needed space in 
the packet. In addition, the filtering material according to the present 
invention facilitates the flow of the edible liquid through the filter 
packet. The filter material is hydrated, that is, provided with absorbed 
and adsorbed water, and to some extent free water. Accordingly, when the 
packet is immersed in cooking oil at a temperature above the boiling point 
of water, the water within the packet is converted to steam. As the steam 
escapes from the packet, it lowers the pressure within the packet to 
facilitate the flow of the edible liquid into and through the filter 
packet. The filter material, as result, in effect pumps the edible liquid 
into the filter packet. 
The inventor has found that a mixture of synthetic hydrated amorphous 
silica and calcined magnesium oxide forms a filter media which functions 
in a superior manner and which is preferred in packets. The synthetic 
hydrated amorphous silica has the chemical notation SiO.sub.2.XH.sub.2 O, 
where X is 10% to 85%. The product is commercially available from the 
Davison Chemical Division of W. R. Grace & Co. under the product name 
Silica III. Synthetic amorphous silica contains no crystalline silica, 
such as quartz, cristobalite or tridymite. It is a dry white powder, 
insoluble in water, having a density of about 30 pounds per cubic foot and 
contains between 99 and 99.6% SiO.sub.2. 
Magnesium oxide has the formula MgO and is a white odorless powder, 80% of 
which will pass through a 100 mesh screen. It also is not soluble in 
water. 
Preferably, the synthetic amorphous silica is hydrated 75-80% by weight, 
and when a packet containing a mixture of hydrated synthetic amorphous 
silica and magnesium oxide is immersed in cooking oil at a temperature in 
excess of the boiling point of water, and preferably on the order of 
200.degree. C., the steam formed by the water adsorbed on the synthetic 
amorphous silica not only physically causes the flow of cooking oil 
through the filter pack, but also functions to rejuvenate spent cooking 
oil. The cooking oil could be heated to a temperature between 
200.degree.-500.degree. F. for the cooking prior to the filtering. The 
presence of steam in the cooking oil facilitates removal of volatile 
ingredients in the cooking oil, but more importantly, the formation of 
steam from the adsorbed moisture frees OH bonds in the silicate to 
facilitate polar attraction of undesirable ingredients within the spent 
cooking oil.

In the embodiment of FIGS. 1 and 2, the packet is formed of a rectangular 
elongated sheet 10 of porous material which is folded over along its 
central transverse axis indicated at 12. A narrow strip of both outer 
edges 14 and 16 are sealed together, by a rows 18 and 20 of stitches 
respectively, and by a layer of adhesive 22 in the form of a narrow strip 
extending from the edges 14, 16 to the rows 18 and 20. 
After the edges 14 and 16 are sealed together, the edge 24 opposite the 
fold 12 is open, and a mass of filtering material 26 in the form of 
granules is poured through the open edge 24 into the cavity formed by the 
fold 12 and sealed edges 14 and 16. Thereafter, the layer of adhesive 22 
is extended in a narrow strip along the inner surfaces of the sheet 10 
adjacent to the edges 24, and a row 26 of stitches is placed along the 
upper edge 24 to completely close the packet and trap the granulated 
filtering material 28 therein. It will be noted that the granulated 
filtering material 28 substantially, but not completely, fills the cavity 
within the sheet 10 of porous material. 
The filter material 28 is selected to take up the contaminants which exist 
in the liquid to be rejuvenated, clarified or refined. The contaminants 
may be absorbed into the filtering material or attracted by polar 
attraction, or some other mechanism not fully understood. Spent cooking 
oil may be rejuvenated with a filtering material consisting of 80% 
hydrated synthetic amorphous silica, 10% synthetic amorphous magnesium 
silicate, 9% diatomaceous earth, and 1% synthetic amorphous silica-alumina 
as disclosed in the U.S. Pat. No. 4,764,384 of John Gyann, entitled 
FILTERING MEDIA AND METHOD OF MAKING SAME, and this material is suitable 
for the granulated filtering material 28 of the present invention. I 
prefer to use for the filtering media 28 a mixture of hydrated synthetic 
amorphous silica and granular calcined magnesium oxide as further 
described above as the filtering media 28, particularly for the purpose of 
rejuvenating spent cooking oil. 
The filter packet of FIGS. 1 and 2 may also be utilized to upgrade or 
recondition many types of liquid including removing undesirable taste 
constituents from fruit juices, coffees and teas, water, beer, spirits and 
other consumable liquids. When the filtering packet is utilized to upgrade 
inexpensive wine, I have found that a mixture of 75% synthetic amorphous 
hydrated silica and 25% diatomaceous earth by weight produces excellent 
results. 
The sheet 10 of porous material is preferably sufficiently porous to permit 
free circulation of the liquid to be filtered but to prevent the filtering 
media 28 from escaping from the cavity formed by the packet. Paper or 
cloth have been found to be suitable materials for the packet. Paper of 
the constituency of conventional filter paper is satisfactory for the 
sheet 10. Any porous sheet material which is inert to the liquid to be 
filtered and which may be sealed into a packet can be used for the sheet, 
but cloth or paper have been found to be most satisfactory because of the 
ease with which the packet can be formed by sewing, or gluing, or both. 
The rows of stitches 18, 20 and 26 may be eliminated from the construction 
of the packet if the layer 22 of adhesive will form a durable tight seal 
at the perimeter of the packet. The inventor has found that a monovalent 
metal silicate is a suitable adhesive for the layer 22 and requires no 
stitching. Added security can of course be achieved by using the layer 22 
or adhesive with the rows of stitches 18, 20 and 26. 
The packets may be of any size, but are preferably sufficiently small that 
the liquid being filtered maintains good contact with all of the filtering 
media within the packet. 
A specific example of a packet constructed according to the present 
invention contains one ounce of filtering media and a porous paper packet 
constructed as shown in the drawings utilizing an adhesive consisting of 
85% by weight sodium silicate and 15% by weight talcum powder and rows 18, 
20 and 26 of stitches, as illustrated. The sheet 10 is of sufficient size 
that the filtering media occupies approximately 80% of the cavity formed 
within the packet. The filtering media itself consists of approximately 
70% synthetic amorphous silica which has been hydrated and 30% magnesium 
oxide by weight. The water associated with the synthetic amorphous silica 
constitutes 80% of the dry weight of the synthetic amorphous silica. The 
synthetic amorphous silica is obtained from the Davison Chemical Division 
of W. R. Grace Company under the tradename Silica Gel and is a dry white 
powder with a density of approximately 30 pounds per cubic foot and a 
particle, size averaging between 30 and 40 microns. 
Sodium silicate or potassium silicate are particularly desirable materials 
for the adhesive since it will withstand high temperature and an 
atmosphere of cooking oil. The adsorbed moisture in the sodium silicate or 
potassium silicate transfers to the paper layer 10 or cloth layer 10 to 
cause the adhesive to set, and at elevated temperatures the adhesive 
becomes glasslike and insoluble. 
It is desirable to add certain ingredients to spent cooking oil in the 
rejuvenating process. One such ingredient is an antioxident, an 
antioxident in the form of palmate, or tochopherols may be mixed into the 
filter media and will pass through the packet into the spent cooking oil 
during the rejuvenating process. Also, it may be desirable in some cases 
to add activated carbon into the packet to facilitate clarification of 
spent cooking oil. The inventor has found that a quantity of activated 
carbon equal to approximately 10% by weight of the filter media may be 
added into the filter media of the packet with improved filtering of some 
types of spent cooking oils. One percent by weight of palmate or 
tochopherols may be added to the filtering media to transfer antioxident 
into spent cooking oil to extend the useful life of the cooking oil beyond 
that achieved by mere filtration. 
FIG. 3 illustrates a portable unit for filtering and rejuvenating the 
cooking oil of a deep fat fryer which is not provided with a drain. 
Similar equipment can be provided for cookers provided with a drain or for 
permanent installations with deep fat fryers. As illustrated, the deep fat 
fryer is shown at 30, and comprises a tank 32 having a bottom 34 and side 
walls 36. The upper end of the tank 38 is open, and adapted to receive a 
basket for the cooking process. 
In accordance with the present invention, FIG. 3 illustrates a portable 
filter machine 40 positioned on the cooker 30. The portable filter machine 
has a cover 42 which extends completely over the open end 38 in order to 
minimize the contact of air on the surface of the cooking oil and to 
prevent steaming and spattering of oil out of the vessel 32. 
The filter machine has an elongated cylindrical housing 44 mounted on the 
opposite side of the cover 42 from the fryer vessel 32, and the housing is 
provided with a central vertical screen 46. The screen 46 divides housing 
into an intake chamber 48 and an exhaust chamber 50. The chambers 48 and 
50 are provided with end walls 52 and 54 which form fluid-tight seals. 
A pump 56 is mounted on the cover 42 adjacent to the end wall 52, and the 
pump communicates with the intake chamber 58 through an aperture 58 in the 
wall 52. A flexible intake hose 60 extends from the inlet end of the pump 
down into the vessel 32 and terminates adjacent to the bottom 34 thereof. 
In like manner, a second tube 62 is sealed through an opening 64 in the 
wall 54 to communicate with the exit chamber 50. A filter packet 66 is 
disposed within the exit chamber 50. The filter packet 66 is identical in 
construction to that described in FIG. 1 and described in detail 
heretofore. 
The pump 56 is an electrically-driven pump, and on excitation of the pump 
56, spent cooking oil from the vessel 32 is pumped through the flexible 
tube 60 and the pump 56 into the intake chamber 48. The spent cooking oil 
flows through the screen 46, leaving particles of food and the like in the 
intake chamber. In the exit chamber, the oil is subjected to the filtering 
action of the filter packet, and is rejuvenated before being returned to 
the vessel 32 through the flexible tube 62. 
The effectiveness of the filtering device depends upon a sufficient 
residence time for the spent cooking oil in the exit chamber. The 
residence time is controlled by the pump 56, and the pump 56 is a variable 
speed pump which allows the operator to adjust the residence time of the 
spent cooking oil in the exit chamber. If the pump operates at a 
relatively high rate, the spent cooking oil must be circulated through the 
intake chamber 48 and exit chamber 50 a relatively large number of times 
in order to become rejuvenated, whereas, the number may be greatly reduced 
by slowing down the speed of the pump 56. 
After the spent cooking oil is rejuvenated, the portable filter mechanism 
illustrated in FIG. 3 is removed from the vessel 32. The housing 44 may be 
disassembled to clean the screen 46 and to replace the filter packet 66 
with a fresh filter packet. 
FIG. 4 illustrates another embodiment of the present invention which is 
intended to clarify, or remove taste ingredients from a relatively small 
body of liquid, such as a glass of wine or fruit juice. The device 
consists of a packet 70 formed of a porous wall 72 and mounted on a handle 
or stick 74. The packet 70 contains a mass 76 of filter material which is 
identical to the filter material 28 illustrated in FIG. 2. Likewise, the 
wall 72 is identical to the sheet 10 of FIG. 2. 
The packet 70 has a flat circular base 78 which is adapted to rest upon the 
bottom of a glass or the like. A conical portion 80 of the wall 72 extends 
from the perimeter of the base 78 to a cylindrical anchoring section 82 
which is cemented or otherwise secured on the stick 74. 
The bitter tasting components of an inexpensive wine, or of a fruit juice, 
can be substantially reduced by merely placing the filter mechanism of 
FIG. 4 in a glass or other container of the material and agitating the 
device to cause flow of the liquid through the filter material. 
There are many other constructions and applications for a filtering 
mechanism utilizing the filter material disclosed herein. There are also 
many applications for a filter packet beyond that set forth herein, and 
the foregoing examples are illustrative of the uses that those skilled in 
the art will develop. It is, therefore, intended that the scope of the 
present invention be not limited by the foregoing specification, but 
rather only by the appended claims.