Frozen french fries process unit operation and machines

A preparation process of frozen French fries is introduced, including potato peeling, trimming, cutting into fries, blanching, dehydrating, par-frying, defatting, cooling and individually quick freezing (IQF).

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brief introduction

Frozen French Fries

Almost all of the French fries we eat at our favorite restaurants are frozen. The market for frozen French fries made from fresh potatoes is large and growing.

The global frozen potato market size is expected to reach USD 74,403 million by 2025, growing at a CAGR of 3.8% from 2018 to 2025. By product, French fries are the largest contributor to the global market, accounting for approximately 40% of the total global frozen potato market share. [Frozen Potato Market Outlook – 2025]

Here, a process for preparing frozen French fries is described, where potatoes are peeled, trimmed, cut into fries, blanched until translucent, dehydrated to remove surface moisture, partially fried, individually quick frozen (IQF) and then packaged and stored accordingly.

Raw potatoes

The characteristics of potatoes are very important in producing good quality French fries.

Raw potatoes for french fries
Size and shape Long tubers larger than 50 mm or oblong tubers are ideal
moisture Dry matter content 20-24%
Reduce sugar Not more than 0.5%
proportion 1.08 g/cm 3 or above, 1.1 is preferred

Frozen French Fries Processing Unit Operations

Potato size grading

If the raw potatoes do not come from a specialist supplier, they should be graded by size before being put into the production programme.

It is very important to use potatoes of uniform size in a process so that they are fried in a uniform size and cook evenly.

Small potatoes are not ideal for making French fries because they result in a lot of short pieces and scraps.

Potato grader

Potato grader

Potato graders are generally designed to grade potatoes of different diameters by varying the gaps between the rollers. The smallest potatoes are selected first and the largest potatoes are discharged last.

The grading size of level 3 and 4 is determined according to the scale of processing.

Peel the potatoes

The potatoes of uniform size are fed into the hopper of the lifting conveyor and then transported to the potato peeling machine.

Brushing and grinding are common methods of peeling potatoes. The time the potatoes stay in the peeler is a critical operation. Too long will grind away a lot of the usable components, resulting in low yields.

Potato peeler

Potato peeler

The brush roller with moderate hardness and softness makes potato peeling smoother, and the independent spraying has good cleaning effect, less damage and more thorough cleaning.

Pruning and sorting

The peeled potatoes are conveyed for further processing. Unpeeled parts are removed by trimming and severely defective parts are removed from the processing line.

Sorting and trimming stations

French fry sorting and trimming station

It is designed to manually sort out substandard potatoes and trim them before slicing.

According to the processing scale, personnel workstations, collection pipelines and trimming conveyors are set up.

French fries slices

The larger the cross-sectional area of ​​the fry, the lower the fat content of the fry, and the rough surface increases the surface area, which increases fat absorption. Ideally, all fries need to be cut to the same size, with a fairly uniform cross-section and roughly uniform length to allow for even cooking (Blumentahl, 1991).

French fries slicer

French fry cutter

French fry slicers are capable of cutting potatoes along the long axis or as close to the long axis as possible to achieve the maximum long cut yield. The size of the French fry can be varied by a variety of blade holders, with 3/8 or 1/2 inch cross-sectional areas being the most popular.

Remove French fry debris

After cutting into French fries, the broken pieces and short pieces must be separated from the product. Otherwise, these unqualified French fries will cause defects such as burning and darkening in color during the par-frying process.

French fry deveining machine

French fry deveining machine

For this purpose, a soft roller with spaced grooves is used to eliminate debris.

Slice washing  

Surface starch that comes out of cut potato slices cause to stick together and colour unevenly. They should be removed by washing immediately.

Potato fries rinsing machine

French fries washing machine

Rich bubbles from strong flow turbine fan make a flexible washing process.

High pressure spray shower which uses fresh water will wash again to have a final cleaning efficiency. The nozzle Angle is adjustable.


Blanching is a processing step whereby potatoes are heated in steam or water for 2 to 3 min. This inactivates enzymes and prolongs the storage life of frozen fries. Moreover, blanching reduces the subsequent cooking time. Blanching also makes the color more uniform after frying and it forms a layer of gelatinized starch that limits oil absorption and improves texture (Moreira, 1999).

The operation standard is that the potato fries are blanched until have a generally translucent throughout.

Potato fries blancher

French fries blanching

Steam is recommended as heating source, it is economic and heating up quickly, the heat is uniform and the temperature difference is small. Thermal oil or electric heating is option.

Blanching temperature and time is set up easily and the mesh conveyor speed is adjustable to meet continuous blanching process.

Cover with water seal device to avoid steam leak, all body shell is filling with insulations, energy saves.


Blanching care must be exercised for both under blanched which will turn off color due to enzymes not inactivated and over blanched which may slough the surfaces. Cooling process is the best way to stop blanching immediately in order to avoid over blanching.

Two stage cooling machine

French fries cooling machine

Fresh water is used as the medium, 1st is pre-cooling and 2nd is deep cooling process.

Fresh water overflow from pre-cooling tank is collected and reused after cooling tower if necessary, while, flow over from 2nd cooling tank will be the back flow to 1st by water pump after filling. Air bubbles are supplied both for 1st and 2nd tank to solve the problem of water temperature stratification, ensure a quick cool with few fresh water consumption.


Surface moisture should be removed from the strips to reduce the load on the fryer and to minimize the rate of hydrolytic breakdown of the fat. The less water quantity evaporated, the short time frying takes. and consequently the lower the oil content of the French fries.

Vibrating dehydrator

French fries dehydrator

It is a preliminary dehydration machine, removal the surface moisture quickly by means of shaking.

Overturn air dryer

French fries air drying machine

Potato fries turn over continuously on the mesh during transport and touch the high pressure blowing air, special blowing blade design to remove or evaporate the extra water by means of air-drying from potato fries in a very short time.

Room temperature air drying with fan is sued in the first stage and hot air drying with fan is in the last stage mesh to ensure fully removing all the surface water. Hot air is heated by fin coil with electric heating.


By means of immersed in a deep fat fryer for a short period of time, around 15 to 60 seconds at a fat temperature of 300 F. to 375 F, The blanched potato strips are converted into the ready to cook French fries. Evaporation of water gives French fries crispy texture exterior while the inside of French fries is cooked.

The fat content of frozen French fries packed for retail trade is usually about 5 to 7 % and that of the par-fried product around 4 %.

Batch operation Deep fat fryer

Fry Pan

Oil (Fat)-water mixture frying technology

Fried food residues are deposited into water throughout a mesh filter. Thus,

Frying oil pollution will be much reducer to result as long service lives and more clean.

Frying fat consumption is unexpected less as the fat in residues will be return to the frying oil before discharge.

Continuous deep fat fryer

Potato chips french fries fryer

A standard continuous deep fat frying fryer includes:

1. an frying tank where the food is submerged in hot oil for frying process, equipped moving mesh belt conveyors and insulation shell ;

2. a gas fire or thermo-conductivity oil external heating unit if electric heating is not possible

3. an oil recirculation system, which pumps the oil through filters or/and external heaters if used and replenishes it from a bulk supply to maintain a steady volume in the frying tank.

4. an cover with exhaust system to remove the vapors emerging contains droplets of oil from the oil tank.

De-fating and Cooling

After deep fat frying, removing superficial fat should be done immediately while the oil temperature remains a high temperature, means of a low viscosity.

And then the par-fired potato fries should be cooled to be ready for the final step, a blast freezing

Vibrating De-fating machine

French fries degreasing machine

Shaking removing the surface oil quickly by means of vibrating motor and damping spring.

Air-cooling machine

French fries cooling machine

Fried fries on the flat mesh are cooled by means of blowing air to remove the surface oil, and cool down to room temperature to meet the quick freezer feeding request in a short time.

IQF (Individual Quick Frozen)

Freezing is the one food process unit operation in which the temperature is reduced until its thermal center reaches −18 ℃, accompanied by the consequent crystallization of water. This results lowering the water activity (aw) of the food, inhibiting the spoilage by microorganisms and/or chemical reactions. [food science].

Blast freezing is a method that fluidized freezes the French Fries at -40 ℃ within 20 min in order to retain texture and to avoid damage as a result of ice crystal formation.


Fluidized bed air blast freezer

Air flow fluidized net freezer

a modified Rapid Freezer, named as fluidized bed freezer, in which cold air is blown up through a wire mesh belt that conveys the particulate products such as peas, beans or shrimp. fluidization occurs. Each food comes in contact with air individually. Resulting an IQF (individually quick frozen) form. Freezing times commonly are as short as 8 to 14 minutes.


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