Understanding Oil AbsorptionDuring Deep-Fat Frying

Prepared by:Ms. Erica G. Penera

Introduction

Frying is considered to be one of the oldest methods of food preparation due to high cooking rates and desirable product characteristics. It is a unit operation which mainly used to alter the eating quality of food. Deep-fat frying involves immersion of food in hot edible oil at a temperature above the boiling point of water for a given period of time.

What are the Common Deep Fried Foods?

MEATSeafood, Poultry, Fish

VEGETABLESCassava, Potatoes- fries/chips

BREAD AND DOUGHEmpanada, dumplings, egg roll, bread stick, fried noodles

How is Food Heated in Deep-fat Frying?

CORE

CRUST

Steam and Volatile Compounds

WATER EVAPORATION

SURFACE

OILABSORPTION

What are the Process Involved in Deep Frying?

Process Involves in Deep Frying

Mass Transfer

Heat Transfer

Simultaneous Heat Transfer and Mass Transfer

CORE

CRUST

CONVECTION:

CONDUCTION:

WATER:WATER VAPOR:

OIL:

HEAT TRANSFER MASS TRANSFER

What are the Equipments and Utensils Used for Deep-fat

Frying?

Deep-Fat Fryers

Two Broad Categories :

1. Batch frying equipment

2. Continuous fryers

Batch Fryers

• Static and smaller (whose capacity can range from 8L-28L of oil).

• This are normally used in catering restaurant and small plants.

Continuous Fryers

• This are used on industrial scale to process large amount of foods (having a throughput that varies from 250kg product to 25,000kg product).

Utensils For Deep-fat Frying

1. Steel Kettle

2. Frying Basket

3. Deep-frying thermometer

What are the Characteristics of Frying Oil?

Frying Oil Characteristics

During deep-frying, fats and oil are repeatedly used at elevated temperatures in presence of atmospheric oxygen and receive maximum oxidative and thermal abuse.

Chemical and physical changes in the oil can prolong the process time, increase the total amount of oil in the product, induce toxicity, and lower food nutritional value.

Good Frying Fat

Stable at high temperaturesSmoke point above 200C and flash point

above 315C Good clean bland flavourEnhance the flavours of the fried product

 

Stability of Fat

More unsaturated fat leading to less stability.

Polyunsaturated oils are less suitable for frying e.g. sunflower, safflower oils.

A frying fat will have greater frying if it is low in linolenic acid, high in oleic acid and higher in saturated fats. 

Temperature Ranges for Deep Fat Frying

Type of Product Temperature of Fat Approximate Time

Doughnuts, Fritters, Oysters, Scallop, Soft-shelled crabs

350-375 F (177-190C)

60 seconds

Croqueetes, Eggplant, Onions, cauliflowers

375-385 F (190-196C)

40 seconds

French fried potatoes 385-395 F (196-201C)

20 seconds

Types of Deep Frying Fats

Tallow Palm Hydrogenated fats Canola Cottonseed Unsaturated Oil: Olive oil, Peanut Oil,

Soybean Oil, Hydrogenated Peanut Oil High Oleic Modified Oils: Sunflower

Product Changes During Deep Fat Frying

Fried products absorb oil during frying and as they cool which contributes to a high fat and high calorie products. Oil content in fried food has been related to initial moisture content, pre-frying treatment, and cooling time.

Shrinkage, Porosity, and Texture Changes

• Fried products will shrink during frying, becoming more porous and crispy after frying.

• Bulk density decreases, and porosity and oil uptake increase with frying time during frying of Tortilla chips.

• The structure of food formed during frying also plays an important role in mechanism of oil absorption.

What are the Factors that Affects Oil Absorption?

Factors Affecting Oil Absorption

Oil Temperature Effect Specific Gravity Pre-frying Treatment Degree of starch Gelatinized Oil Quality

Oil Temperature Effect

• Higher temperature leads to a faster crust formation thus favoring the conditions for oil absorption.

• As the moisture is reduced with frying time, the ratio of oil content to the amount of water removed becomes independent of the oil temperature.

Specific Gravity

• Potatoes with high specific gravity (˃1.10%) and dry matter (>24.0%) produce chips with lower oil content.

• The thicker the potato slice, and thus the smaller surface are relative to the chip volume, the lower will be the chips volume oil content

Pre-frying Treatment

• Blanching makes the fries’ color more uniform, reduces oil uptake by gelatinizing the surface starch, shortens frying time, and improves the fries’ texture.

• Removing of some of the water prior to frying can reduce oil uptake after frying

Degree of Starch Gelatinized

• The higher the degree starch gelatinized the more the oil will be at the surface of the food than at the core.

Oil Quality

• Used or poor quality frying oil will make the product look oilier although the total oil content will be the same as those fried in fresh oil.

• Most of the oil absorbed by chips fried in degraded oil is concentrated on the surface.

• The higher viscosity of the degraded oil could cause the oil to adhere to the products surfaces

Conclusion

In conclusion, we can say that deep fat frying is a complex process that involves heat and mass transfer mechanisms and a variety of physical and chemical changes in both food and frying oil. Understanding the mechanism of oil uptake is crucial to product quality control since oil is one of the most important quality factors of fried foods in deep-fat frying process.

THANK YOU. . .