Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to a process for the preparation
` of a frozen potato product.
Applicants Canadian Patent No. 913,985 describes a
process for the preparation of a frozen slightly fried ("braised")
potato product from which after thawing may be prepared a
"Rosti" by heating the product. According to this process peeled
potatoes are, if necessary, cut to pieces of roughly equal sizes,
the pieces are heated in water until the hearts of the pieces
have acquired a temperature of 60-80C., the preheated pieces
are cooled until the hearts of the pieces have acquired a
temperature below 25C, the pieces are heated in water or steam
of 100C for such a time that when the temperature T in C,
measured in the hearts of the pieces, is plotted in a graph
,' against the heating time t in minutes, the area which is
~t
represented by the definite integral O~ Tdt amounts to 300-900C
minutes, the heated pieces are cooled, if desired, and comminuted
to cuttings, e.g. by grating, the cuttings, with the addition
of fat and, if desired, salt, cheese, bacon or onions, are
slightly braised, the slightly braised cuttings are formed into
a cake, and the cake is frozen. Although according to this
- process the preheated and subsequently cooled potato pieces areheated, this is no normal cooking. After thawing the product
obtained in this way is not yet equal to a "Rosti" but it becomes
only a "Rosti"
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after ~eatin~ or frying. Th~ product obtained by the
process i5 a frczen "preliminary" product. Alternatively,
according to the known P~Ocess the cake may be ~ried
~ on both sides before freezing. In this way the product
; 5 obtains an attrac~ive appearance and is then a "Rosti"
ready for use, whic~ is frozen. Af~er thawing it is
; mer-ely heated and not fried.
It has now been found that a preliminar~ product
which is equivalent to the above-mentioned preliminary
product, optionally in the form of loose pieces instea~l
of in the form of a cake, may be prepared in a smaller
,~ number of steps than according to the above-mentioned
~, known process.
The process according to the invention is charac-
; 15 teriz~d in that
; (a) pQtatoes are peeled;
(h) i` necessary, cut to pieces of roughly equal thic~ness
or sizes;
(c) heated in water ~til the hearts of the pieces have
acquired a temperature of 60-8QC.;
(d) the pieces are cooled with air &nd/or cold water
until the hearts of the pieces have acquire~ a
temperature below 25C.;
(e) tne pieces are heated in warm water or steam
having a temperature of 95-130C. for such a time
that when the temperature ~ in C., measured in the
~earts of the pieces, is plotted in a graph against
the heating time t in minutes, the area which is
represented by the definite integral ~ mdt
amounts to ~00-900C. minutes;
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(~) i F ~esirPd~ the heatsd pieces are cooled;
(~) the pieces are comminuted to cuttings;
(h) i~ desired, the cuttings are mixed with a fat
ard, if desired, salt and/or cheese, bacon or
onions;
(i) the cuttings obtained in step (g) or (h) are
cooled, if desired, and frozen while being kept
in continuous movement; or
(j) the cuttings obtained in step (h) are slightly
~ braised, cooled while being kept in continuous
movement to prevent cohering of the cuttings,
if desired, and frozen; or
(k) the cuttings obtained in step ~h) are formed
into a cake by slightly pressing, the cake is
fried on one side or on both sides, if desired,
the cake is cooled, if desired, and frozen
The above-mentioned freezing treatments are
carried out in a deep-freeze.
~lthough the product obtained in step (k) of
the process according to the invention is in the form
of a cake, it is obtained with the omission of slightly
braising the cuttings mixed with fat and of cooling of
the slightly braised cuttings. In tnis respect the
; process according to the invention is more simple from
a technical point of view and therefore more economical
than the known process.
It is still more economical when the forming of
a cake before freezing is omitted, which is the case
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in the embodimçnt according to step (i) or (~).
According to step (;) the cuttings have been slightly
braised before freezing; according to step (i) sligh'ly
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bra sir.g is also omitted. In both c~ses the product is
obtained in the form of loose cuttings. This is particular-
- ly advantageous from the YieW-point of packaging of
the product. A cake has to be packaged o~ a packaging
machine which has been constructed especially for this
purpose, whereas loose cuttings can be packaged on a
; usual packaging machine, for instance in bag~ or pouches~
~`~ For carrying out the process according to the
invention potatoes having a specific gravity of no
more than 1.090 are preferably used as starting material,
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because then a product having the desired palatable
texture is obtained. ~he optimal specific gravity
depends on the variety of potato.
~he potatoes are peeled, and the eyes and damaged
or diseased parts are cut away. ~o achieve an effèct
; which i8 as homogeneous as is possible of the pre-
heating step (c) and the heating step (e), it is
desirable for the potatoes to be cut into as regular
pieces as is possible, which pieces have about equal
size5 or at least equal thickness, for example, by
cutting them into slices. The thickness of the slices
~ay be up to 25 mm The lo-~er limit of the thickness
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of the slices may be equal to the thickness of the
cuttings to be made therefrom in step (g). ~his thick-
; 25 ness may be about 1 mm. It is also possible to use
; small potatoes of sizes of no more than 25 mm. provided
they are of about equal siæe Preferably, the thickness
; of the slices or the size of the pieces Qr of whol-
potatoes is 15-25 mm. because then heating is controlled
easily.
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I)uring the fo7lowillg preheating step it is
essential for the heart of each of the pieces of
potato to reach a temperature of 60-80C., and
; preferably 65-75C. ~o obtain this effect the piecesof potato are put in hot water, the temperature of
- which is not essential, so lon~ as it is high enough
SG that the desired temperature in the heart of the
pieces of potato will be obtained and the starch in
the cells will be gelatinized. It takes about 15 minutes
for the desired te~perature bO be oDtained when deali~g
with pieces having a thickness of 15 mm, and about
22 minutes with pieces having a thickness of 25 mm,
when water is used having the temperature to be reached
i~ the pieces.
Cooling the preheated pieces of potato until
the hearts of the pieces have acquired a temperature
below 25C may be achieved by immersion in, or spraying
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with cold water. Air may also be allowed to flow along
the pieces, in combination with coGling with cold ~ater,
if desired.
; Then the cooled piecPs of potato are heated in
hot water or steam having a temperature of ~5-1~,0C
To determina whether the heat treatment was sufficient,
the course of the te~perature ~ in C. is tak.en in the
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heart of the pieces of potato and plotted on a graph
against the heating time t in minutes. There is thus
a curve obtained which includes, with the abscissa of
time, the ordinate of temperature and a line drawn
through a given point on the abscissa of time parallel
with the ordinate of temperature, an area which is
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measursd in C~ minutes by the definite integral
indicated in step (e). ~his area should be 300-900C.
minutes ~he best results are obtained with an area
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of 450~750C minutes. For slices having a thickness
; 5 of 15 mm and being heated in steam of 100C an area
was determined of 532C. minutes after 8 minutes,
and for slices having a thickness of 25 mm an area
of 550C minutes after 10 minutes. It is to be
understood that these calculations need not be
repeated at each heating process. When, after a
; number of measurements during the heating process of
pieces or slices having a given thicknes in a given
heating apparatus, the shape of the heating curve is
sufficiently accurately known, it may be determined
from the plotted graph how long the heating process
should be continued in future runs for pieces with
that predetermined thickness to obtain a desired value
of the area included.
Measuring the temperature in the heart of the
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- 20 pieces of potato during preheating, cooling and further
heating is suitably carried out with a thermocouple.
After this heating treatment the pieces o~ potato
may be cooled. ~he advantage of cooling is that the
heated material may be s~ored for some time, and it is
also easier to handle during the subsequent comminuting
step,
Comminuting may be effectively carried out with
the aid of a grate or a similar apparatus. Suitable si3es
for the cuttings are a length of 20-60 mm, a width of
4-6 mm, and a thickness of 1-3 mm
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The cuttings obtained may be further treated in several
ways.
The most simple treatment is freezing the cuttings in
a deep-freeze either directly or after cooling. During freezing
the moist cuttings have to be kept in continuous movement to
prevent them from freezing together. It is also possible to mix
the cuttings with a fat, e.g., lard, margarine or butter, and
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optionally also with cooking salt and/or pieces of cheese,
bacon or onion before freezing.
Furthermore, the cuttings mixed with fat and optionally
-; other additives may be slightly braised for 2-lO minutes on a
heated surface, preferably in the apparatus described in Dutch
~ patent 141,079. This braising, also called "browning" in
practice, may also take place in a rotating drum, the wall of
which is externally heated, or in a mixing trough, a ribbon mixer,
a conveyor oven or a conveyor chute. The longer the braising
process, the shorter the heating process in step (e) should be.
In other words, a lower value of the area included by the
temperature-time curve within the given limits should be kept on,
and vice versa, when braising is carried out shorter or is
completely omitted a higher value of this area should be kept on.
, After the cuttings have been braised, they are cooled
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while being kept in continuous movement to prevent them from
~ cohering by the fat present on the cuttings. The most efficient
;~ method of cooling is blowing or sucking cold air upwardly
through a layer of braised cuttings in such
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~; a way that they attain a fluidized state, In thls
^ way the heat is carried off quickly and due to the
movement the cuttings do not cohere but form a loose
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mass,
After the cooling process, the pieces are deep-
frozen,
Finally, the cuttings optionally mixed with fat
and other additives may be formed into a round cake,
without braising, The cake is formed by slightly pressing
a quantity of cuttings, Suitably, the diameter of the
cake is about 25 cm. for the cake to be easily transferred
to a frying pan, The thickness may be about 3 cm, ~he
cake is froze~ in a deep-freeze,
~he surface of the loose cuttings or of the
cake may not dry out, and this may be prevented by
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'` sealing the cuttings or the cake from the air in a
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known manner, Preferably, the cuttings are packaged
in bags of plastic foil or of aluminum foil, and the
~ cake is wrapped in plastic foil or aluminum foil,
': 20 Preferably~ the cake is formed during packaging and
~l before the optional cooling step and before freezing,
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because then packaging and forming the cake can take
place simultaneously, ~he packaged frozen product may
~! be s~ored for quite a time in the deep-freeze compart-
ment for frozen foodstuffs.
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In order to make the product prepared according
to the invention ready for consumption it need only
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to be thawed and slightly fried, In so far as the
product consists of loose cuttings, it is made into
- 30 a cake by slightly pressing after slightly frying,
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In household this fryin may take place in a frying pan. After
being fried on one side, the cake is turned and fried on the other
side. The time of fr~ing is somewhat dependent on the thickness
of the cake and from the fact whether step (j) has been carried
out. When the thickness is about 3 cm, the first side should be
fried during about 8 minutes and the second side during about
6 minutes. If the cake before freezing is fried on one side or
on both sides, it is sufficient to heat it up. This may be done
; in a high frequency oven during 2-2.5 minutes, in a hot air oven
at 150C during 10-15 minutes, or in an electrical or gas-heated
household oven at 250C during 40 minutes.
The following examples illustrate the invention.
EXAMPLES 1 to 16
Potatoes of the Bintje variety (specific gravity 1.084)
were peeled in a steam peeler, then the eyes and the unsound parts
were removed. The potatoes were then cut to slices having a
thickness of 20 mm.
; The slices were heated in water of 75C for 15 minutes,
at which time the heart of the slices had acquired a temperature
20 of 70C. The preheated slices were then cooled in flowing cold
water until theheartof the slices had acquired a temperature of
19C. This was the case after 19 minutes. Subsequently, the
slices were heated in steam of 100C for 10 minutes, the area of
~ the definite integral Ov~ Tdt being 690C minutes,
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The heated slices were divided into portions
and each of the portions was processed further as
- indicated in the Table. Cutting accordin~ to step(g) as indicated hereinbefore was accomplished in
the cutting cylinder of an Alexander-Werk apparatus
for kitchen use. This cylinder has a stationary wall
with cutting openings, like those of a kitc~.en ~rate,
across which openings the p-:tato slices to be cut
are guided by a rotor. The cuttings had a crescent-
shaped cross section perpendicularly to the longitudinal
direction. The width of the cuttings was 4-6 mm, the
thickness 1-3 mm, and the length 20-60 mm.
In the head of the Table the letters in parentheses
correspond with the steps of the process according to
; 15 the invention indicated hereinbefore by the sane lettersa
...;
In the Table has been indicated whether, and eventually
in -~lhich manner a certain step was carried out. The
indication "+" means that the step mentioned in the
head of the Table wa! carried out; "-" means that it
; 20 was not carried out.
Freezing was carried out in a fluidized bed at
-40C., except in the Examples 7, 8, 15 and 16, where n
a cake was formed.
In the Examples 3-8 and 11-16, wherein in step
(h) the c-~ttings were mixed with fat, 0.1% by weight of
antioxidant, calculated on the fat, was additionally
added. The antioxidant was a mixture of butylhydroxy-
anisole, n-propyl gallate and citric acid, which was
dissolved before in a portion Or the quantity of fat
i 30 to be mixed with the cuttings~
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After two months storage at -20C a Rosti was prepared
from each of the products obtained according to the Examples 1
to 6 and 9 to 14 by melting a small pat of margarine in a frying
pan, putting 500 g of frozen cuttings in the pan and heating for
3 minutes on a large flame while turning the cuttings. Then a
cake was formed by slightly pressing the heated cuttin~s. The
cake was fried on both sides on a moderate flame for 3 minutes
to give a golden brown crust.
~ rom each of the products obtained according to the
; lQ Examples 7 and lS a Rosti was prepared by frying the cake in a
~rying pan, with the addition of a small pat of margarine, on
,i~ one side for 8 minutes and on the other side for 6 minutes.
Each of the products obtained according to the Examples
8 and 16, which is already a Rosti, was heated. This was done
in a high frequency oven for 2.5 minutes, or in a hot air oven
at 150C for 14 minutes respectively.
In all these cases a palatable Rosti having the desired
texture was obtained. The individual potato cuttings were well:"
perceptible both visually and on the tongue.
It will be understood that the claims are intended
to cover all changes and modifications of the preferred embodiment
of the invention, herein chosen for the purpose of illustration,
which do not constitute departures from the spirit and scope
of the invention.
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