Process for preparing frozen par-fried potatoes

A process for preparing frozen par fried potatoes which, when finish fried, have a crisp surface texture and a mealy internal core, and remain crisp and rigid for extended periods of time after finish frying. Potatoes which have been peeled, trimmed, cut into strips and blanched, are subjected to a two stage drying procedure, in which the strips are first exposed to high velocity ambient air for a period of time sufficient to reduce their weight by about 8%-15%, and are then dried in circulating heated air to further reduce the weight of the strips by an additional 8%-15%. After drying, the potato strips are maintained in a quiescent state for a short period of time to permit equialization of moisture distribution in the strips, and are then par-fried, frozen and packaged.

BACKGROUND OF THE INVENTION 
This invention relates to the production of partially fried, frozen potato 
strips, which when finish fried provide french fries having improved 
textural characteristics. More particularly, the invention relates to a 
process for producing frozen par-fried potatoes which remain crisp and 
rigid for extended periods of time after finish frying. 
A sizeable market has developed in recent years in the institutional food 
trade such as restaurants, fast food stores and the like, for frozen, 
partially fried potato strips which require only a brief period of further 
cooking before serving. Such potato products, which are generally referred 
to as par-fries, are produced by peeling, cutting and trimming raw 
potatoes into strips of a suitable size, which are blanched in steam or 
hot water to partially cook the potatoes. The blanched strips are then 
partially fried (par-fried) in hot fat or oil and are frozen. Such frozen 
par-fries are prepared for consumption by finish frying in deep fat or oil 
for a short period of time, usually about 1-3 minutes. The use of such 
frozen par fry potato strips offers convenience and savings in labor 
costs, since they need only be removed from the package and finish fried 
for a short time, thereby eliminating the necessity for washing the 
potato, peeling, cutting it into strips and frying for extended periods of 
time, as is required when french fries are prepared from raw potatoes. 
However, par fried potato strips available heretofor commonly suffer from 
the disadvantage that when prepared for consumption they are unstable as 
to texture. Thus, immediately after finish frying, the potato strips have 
a desirable crisp texture, but become limp and soggy within a few minutes 
after preparation. Such limpness of the french fries results in 
objectionable appearance, taste and texture and is a primary feature by 
which consumers identify a poor product. 
A number of solutions have been proposed in order to improve the crispness 
and rigidity of par-fried potatoes after finish frying. For example, the 
surface treatment of potato strips with firming agents such as modified 
starches, gums, alginates, calcium salts, and the like has been suggested 
to improve the crispness of the strips after finish frying. The results 
obtained by such surface treatment procedures, however, have been 
successful to only a limited degree and vary with the condition of the raw 
potatoes used. As a result, control of surface crispness and rigidity of 
the finished fries is largely dependent upon the quality of the raw 
potato, which varies throughout the year, and may be seriously affected 
during the production of the par-fried potato strips. U.S. Pat. No. 
3,397,993 discloses a process for producing frozen par fried potato strips 
in which the strips are first blanched to a translucent condition and are 
then dried in hot air (150.degree.-350.degree. F.) to remove between 
20%-30% moisture prior to par frying and freezing. U.S. Pat. No. 3,649,305 
discloses a process in which potato strips are dried in hot air 
(150.degree.-350.degree. F.) to remove between 10%-30% moisture, after 
which the strips are blanched, par fried and frozen. 
The present invention provides a process for the production of par-fried 
potato strips which have a crisp surface layer and a mealy inner core 
after finish frying and which retain their surface crispness and rigidity 
for an extended period of time after finish frying. In addition the 
present process provides a significant savings in the amount of energy 
required to produce the product, as compared to prior art procedures which 
involve drying of the potato strips in hot air prior to par frying. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, raw potatoes are washed, peeled, 
trimmed, and cut into french fry sized strips in the usual manner. The raw 
potato strips are then blanched, to inactivate enzymes and partially cook 
the potato strips, by conventional procedures, such as by using hot water 
or steam. Upon completion of blanching, the strips are dehydrated in a two 
stage drying procedure. In the first step of this drying procedure, the 
blanched strips are exposed to a stream of high velocity ambient air for a 
period of time, typically 5-30 minutes, to remove sufficient moisture to 
reduce the weight of the strips by about 8%-15%. Both surface moisture and 
internal moisture are removed from the strips during such contact of the 
strips with high velocity ambient air. The strips are then subjected to 
drying in heated air to further reduce the moisture content of the strips 
by about 8%-15% by weight, with the total moisture loss in both drying 
steps being about 18%-26% by weight. 
After hot air drying, the strips are allowed to remain in a quiescent 
state, subjected to minimal air movement, for a short period of time, to 
equalize the distribution of moisture in the strips. During this period 
moisture from the core of the strips diffuses into the outer surfaces, to 
provide substantially uniform distribution of moisture in the strips. 
Thereafter the strips are immersed in a deep fat fryer to further reduce 
their moisture content and to partially fry the strips. The par-fried 
strips are then frozen and packaged. 
The frozen par-fried potato strips thus produced are prepared for 
consumption by finish frying in a deep fat or oil bath for a short period 
of time, for example 1.5 to 3.5 minutes, at a temperature of about 
300.degree. F.-375.degree. F. The resulting french fried potato strips 
have a superior texture, crispness, taste and color, having a crisp, rigid 
surface layer and a mealy inner core. In addition, the french fries thus 
prepared retain their crispness and rigidity for extended periods of time 
after finish frying, without becoming limp and soggy. 
DETAILED DESCRIPTION OF THE INVENTION 
In the practice of this invention, raw potatoes are first subjected to the 
usual preliminary steps of washing, peeling and trimming. In order to 
achieve the desired end product, that is, par-fried potato strips which 
retain surface crispness and rigidity for an extended period of time after 
finish frying, it is generally preferred that the raw potatoes have a 
relatively high solids content, that is, about 20% or higher. However, 
potatoes having a lower solids content, for example between about 18% and 
20%, may also be used in the present invention. After trimming, the 
potatoes are cut into strips which may be from about 1/4 to 1/2 inch 
square in cross-section, or into larger cuts such as 1/2 inch by 3/4 inch 
in size. 
The strips thus obtained are blanched according to conventional procedures 
in order to inactivate enzymes which cause discoloration in potato solids, 
to leach sugars from the strips and to partially cook the potato strips. 
While the time and temperature of blanching may be adjusted to variations 
in the raw potatoes, typically the strips are blanched by immersion in hot 
water, at about 160.degree. F.-210.degree. F., for 2-15 minutes, with a 
temperature of 170.degree. F.-190.degree. F., for 4-9 minutes being 
preferred. Alternatively, the potato strips may be blanched in steam, at 
atmospheric pressure, for about 2-10 minutes. If desired, the sugar 
content of the potato strips may be adjusted for color control by 
well-known procedures at this point in the process. 
After blanching, the potato strips are dehydrated in a two stage drying 
procedure to remove sufficient moisture to reduce the weight of the potato 
strips by about 18%-26%. Thus, the blanched potato strips are carried, 
such as on an endless screen conveyor belt, through a two stage drying 
unit in which the strips are first carried through an ambient air drying 
section and then through a hot air drying section. In the first or ambient 
air drying section, the strips are contacted with high velocity, 
circulating ambient air for a period of time sufficient to remove from the 
strips about 8% to 15% by weight moisture, preferably between about 9% and 
12%. As used herein, the term "ambient air" means air having a temperature 
of approximately the same as the air in the production facility 
surrounding the drying unit. Generally this air will be at a temperature 
of about 70.degree. F. to 75.degree. F., but may be slightly higher, for 
example up to about 90.degree. F., at times, such as during summer months, 
if the production facility for the product of this invention is located in 
an area in which high outside temperatures are encountered. Ambient air is 
used in this initial drying step in order to effect slow removal of 
moisture from the potato strips. Such inital slow removal of moisture from 
the strips is essential in the process of the present invention. 
In accordance with a preferred embodiment of the invention, the blanched 
strips are deposited as a continuous stream on an endless screen conveyor 
belt and form on the belt a loosely laid bed of potato strips having a 
thickness of about 2-8 inches, preferably about 4-5 inches. As the bed of 
potato strips is carried through the ambient air drying section, ambient 
air is blown downwardly through the bed at a rate of about 200-400 feet 
per minute face velocity, preferably between about 250-300 feet per minute 
face velocity, to facilitate removal of moisture from the strips, with 
substantially all of the surfaces of the strips being contacted by the 
high velocity ambient air. Ambient air drying of the strips is continued 
until sufficient moisture has been removed from the potato strips to 
reduce the weight of the strips by about 8% to 15%. Of the moisture loss 
effected during this ambient air drying of the strips, about 3%-5% is 
surface moisture with the remainder being internal moisture loss. 
The period of time the strips are in contact with the high velocity ambient 
air in order to effect the desired moisture loss in the initial drying 
step will of course depend on a number of factors, such as the initial 
moisture content of the potatoes, the temperature of the air, the velocity 
of the air flow, the degree of saturation of the air and the like, and can 
be readily established. Typically the potato strips are contacted with 
70.degree. F. air for 5-30 minutes in order to effect the desired moisture 
loss. 
Upon completion of the ambient air drying step, the potato strips are then 
further dehydrated in a second drying step by subjecting them to high 
velocity heated air to further reduce their moisture content. In this 
second drying step the strips are contacted with hot air having a 
temperature of between about 170.degree. F. to 230.degree. F., for 4-20 
minutes, preferably 190.degree. F.-210.degree. F., for 8-10 minutes, to 
further reduce the weight of the potato strips by moisture loss by an 
additional 8%-15%, preferably 12%-14%. Thus the bed of strips is carried 
on the conveyor belt from the ambient air drying section into the hot air 
drying section where hot air having a flow velocity about the same as in 
the ambient air drying section, is blown downwardly through the bed so 
that all surfaces of the strips are contacted by the heated air. If lesser 
amounts of moisture are removed or substantially lower air temperatures 
are used in this step, the strips, when finish fried, will not develop the 
desired crispness and rigidity characteristics. The removal of more than 
about 15% moisture in this second drying step is to be avoided since it 
results in the strips being over dried which promotes blistering of the 
surfaces of the strips during the par fry step and the production of 
french fries having an extremely leathery surface layer. 
Upon completion of the hot air drying step, the potato strips are 
maintained in a quiescent state for a short period of time, usually about 
4 to 6 minutes, to facilitate equalization of moisture distribution in the 
strips. During this period, the strips are subjected to minimal air 
movement, with moisture from the interior of the strips migrating to the 
outer surfaces. In this manner the distribution of moisture between the 
core and the outer surfaces of the strips becomes more uniform to 
facilitate additional moisture removal during frying and to prevent 
expansion of the core and blistering of the outer surfaces of the potato 
strips during deep fat frying. Preferably, the bed of potato strips is 
maintained in a quiescent state in an enclosed space in which there is 
little, if any, air movement. While no attempt is made to heat the air in 
this enclosed space, this temperature may rise to about 140.degree. F., or 
higher due to the sensible heat of the potato strips being processed 
therein. According to one embodiment, the bed of potato strips is carried 
on the endless conveyor from the hot air drying unit through an enclosed 
unheated unit in which the strips are kept for about 4 to 6 minutes to 
permit such uniform moisture distribution in the strips. 
Thereafter, the potato strips are par-fried by immersing them in a deep fat 
fryer for a short period of time, for example 20 to 90 seconds at a fat 
temperature of about 325.degree. F.-390.degree. F. During par-frying, 
additional moisture is removed from the strips, so that upon completion of 
par-frying, the potato strips have a solids content of between about 
30%-40%, preferably 33%-38%. 
After par-frying, the strips are frozen by cooling them to a temperature of 
about 0.degree. F. to 25.degree. F., by conventional procedures such as on 
a continuous belt freezer in a freezing tunnel. 
When the par-fried strips are prepared for consumption they are finish 
fried, from the frozen state, in deep fat for about 11/2 to 31/2 minutes 
at a temperature of about 300.degree. F., to 375.degree. F., to develop 
color and crispness. 
The potato strips, after finish frying, have a crisp, rigid surface which 
is golden brown in color and a mealy internal texture with improved 
mealiness, without excessive separation between the core and the outer 
surfaces. French fries prepared from the par-fried strips of this 
invention retain these internal and external texture characteristics for 
extended periods of time after finish frying, without becoming limp and 
soggy. This enables the restaurant or fast food outlet to finish fry the 
par fries in advance and hold them for extended periods of time until 
needed, without any significant adverse effect on the texture of the 
french fries served to its customers. 
The two stage drying procedure of the present invention, in addition to 
providing a product having superior internal and external texture 
characteristics for extended periods of time after finish frying, also 
enables frozen par fries to be produced with considerably less energy 
consumption than is required in the production of frozen par fries in 
which only a single hot air drying step is used. Thus, the removal of a 
total of 18%-26% moisture, when carried out in a two stage drying 
procedure in which the strips are first contacted with high velocity 
ambient air to remove about 8%-15% moisture and are then contacted with 
hot air (190.degree. F.-210.degree. F.) to remove an additional 8%-15% 
moisture, requires about 25%-30% less energy than is required to remove an 
equivalent amount of moisture in a single stage, hot air dryer. This 
reduction in energy consumption provides the process of the present 
invention with a distinct economic advantage over the procedures used 
heretofor.

The invention is further demonstrated by the following examples. 
EXAMPLE I 
A random sample of Russet Burbank variety potatoes, having an average 
specific gravity of 1.075, was washed, peeled, trimmed and cut into strips 
approximately 11/32" square in cross-section. The resulting raw potato 
strips were then blanched by immersion in hot water (181.degree. F.) for a 
period of 7-8 minutes. After blanching, the strips were drained and placed 
on a screen as a loosly laid bed of strips. High velocity ambient air 
(72.degree. F.) was blown downwardly through the strips for a period of 12 
minutes, with the resultant weight loss of the potatoes being 10.4%. The 
potato strips were then contacted with a stream of hot air (200.degree. 
F.) for a period of 15 minutes to further reduce the weight of the 
potatoes by 14%, for a total moisture loss of 24.4%. Upon completion of 
hot air drying, the strips were maintained in a quiescent state for about 
4 minutes during which time the strips were subjected to minimal air 
movement. Thereafter the potato strips were par fried in hot oil 
(360.degree. F.) for 45 seconds and were then frozen. The par fried strips 
thus produced had a solids content of 37.6%. Thereafter the frozen strips 
were placed in a frying basket and immersed in a deep fat frying bath and 
were finish fried at 360.degree. F. for 23/4 minutes. The resulting french 
fried potato strips had a crisp outer surface and a mealy internal core. 
As the product cooled, these characteristics were maintained, with the 
strips remaining crisp and rigid, and exhibited no evidence of limpness or 
sogginess. 
In order to provide a basis for comparison, a second batch of french fried 
potatoes was prepared according to conventional procedures. That is, the 
raw potato strips were blanched, par fried, frozen and finish fried using 
the same procedure and conditions as was used in processing the first 
batch of strips. However, the strips were not subjected to drying prior to 
the par-fry step. The resulting finish fried strips were crisp when 
removed from the fryer, but after 3 minutes began to exhibit undesirable 
limp and soggy units. 
EXAMPLE II 
A quantity of Russet Burbank variety potatoes, having an average specific 
gravity of 1.078, was washed, peeled, trimmed and cut into strips about 
1/4 inch square inch cross-section, using conventional procedures. The 
potato strips were then blanched at 176.degree. F. for seven minutes by 
immersion in hot water. The blanched strips were drained and subjected to 
a two stage drying procedure in which a loose bed of the strips was first 
contacted with a stream of ambient air (73.degree. F.) for eight minutes, 
which reduced the weight of the strips by about 9%, and the bed of strips 
was then subjected to a stream of hot air (200.degree. F.) for eleven 
minutes to further reduce the weight of the strips by an additional 13%. 
After hot air drying, the strips were allowed to remain in a quiescent 
state for 5 minutes after which they were par fried in hot oil 
(360.degree. F.) for 30 seconds and then frozen. The par fried strips had 
a solids content of 36.1%. The frozen strips were subsequently finish 
fried in hot oil (340.degree. F.) for 21/4 minutes. The resulting french 
fried potato strips exhibited a crisp but tender shell, free of a 
leathery, tough character. This characteristic shell remained as the 
strips cooled.