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All About Deep Frying

Are soggy french fries are really oily french fires? Check out why temperatures or crispiness will tell us only lies!

What is Deep Frying?

In the process of deep frying, two primary objectives are achieved.

  • Dehydration
    As soon as the food makes contact with the hot oil, a reaction ensues, leading to the formation of bubbles. These bubbles represent water pockets that swiftly transition into vapor, rising from the food, ascending through the oil, and ultimately escaping into the surrounding environment. The higher the frying temperature, the more vigorously these bubbles emerge.
  • Simultaneously, the Maillard reaction takes place.
    During this reaction, proteins and carbohydrates undergo degradation and recombination, resulting in the development of the brown hues and flavors that are commonly associated with well-fried foods.

How to deep fry?

To prevent foods from acquiring a tough and fibrous texture during the frying process, they are frequently coated with a protective insulating layer of batter or breading. This results in a harmonious combination: tender, steamed interiors and an outer layer that is crisp, brown.

Interestingly, the popular belief that lower oil temperatures lead to increased oil absorption by foods is unfounded. In reality, the extent to which a piece of fried food absorbs oil is directly linked to the quantity of moisture that is expelled, which, in turn, is influenced by the cooking temperature and the final cooking temperature.

Yet, the perception of greasiness intensifies when frying temperatures are lower. Soggy fried foods, which retain a mixture of oil and residual water in their coating, yield a sensation of softness and oiliness on the palate, even though their actual oil content is lower than that of properly fried food.

Why is the sogginess?

The primary distinction between frying in oil and cooking in water revolves around temperature. Under atmospheric conditions, water can only be heated to 212 °F / 100°C, whereas deep-frying in oil typically occurs within the range of 330-380°F / 165-193°C.

The food’s surface and interior become quickly dried out by the high temperature of the oil, resulting in the crispy texture. This dehydration process contributes to the food’s crispiness.

It’s not merely about water vapor transferring out of the food; some of the frying oil also gets absorbed by it.

Nevertheless, the oil doesn’t penetrate deeply into the fried food. It primarily remains on the surface of the fried product and isn’t absorbed significantly during deep-frying, but rather during the subsequent cooling phase.

Oil absorbtion rate

The rapid release of water vapor while deep-frying creates a barrier that restricts oil from migrating into the food. Once the food is removed from the fryer, the system stabilizes as no further water evaporates, allowing excess oil on the surfaces to be absorbed by the food.

During the immersion of tortilla chips in oil, only 20% of the total oil content is absorbed. However, a substantial 64% of the total oil content is absorbed during the subsequent cooling phase after frying.

Therefore, for a healthier deep-frying process, allowing the food to properly drain after frying is more crucial than controlling the oil temperature. Allowing the food to rest briefly on a paper towel after frying helps maintain its crispiness without absorbing excess surface oil.

Moisture Content

An elevated initial moisture content in food results in greater oil absorption. This might appear contradictory to the notion that evaporating water prevents excessive oil absorption during frying. However, the oil tends to occupy the space left behind by the evaporated water.

The higher the initial water content in the food, the greater the potential oil absorption. Scientific experiments have demonstrated that pre-dried food absorbs less oil during deep-frying. However, the primary reason for this appears to be the structural alterations occurring on the food’s surface during drying, which diminish oil permeability.

Microstructure of the crust

The less porous a food’s surface, the lower its capacity for oil absorption during deep-frying.

Coating foods with breadcrumbs or flour can enhance crispiness but significantly increases oil absorption. These coatings create highly porous surfaces, thereby expanding the overall surface area of the food.

Surface area

Generally, the greater a food’s surface area, the more oil it will absorb. For instance, chips absorb more oil than French fries, while French fries absorb more oil than a doughnut.

Therefore, if aiming for “healthier” French fries, cutting them into thicker pieces can be beneficial. This principle applies to chicken as well. Wings possess a considerably higher surface-to-meat ratio compared to leg quarters or breast meat. While they offer a flavorful crust, it unfortunately contains a high amount of oil saturation.


Surprisingly, there isn’t a direct link between oil temperature and oil absorption.

Chips and French fries are the most commonly studied fried foods, revealing no disparity in oil absorption when fried at 280 °F or 365°F / 140° or 185°C. They absorb an equal amount of oil at both temperatures.

Furthermore, certain studies suggest that foods fried for an extended period at a higher temperature might contain more oil. For instance, if French fries are fried for at least 3 minutes, they absorb more oil at 340 °F compared to 310 °F.

Scientists attribute this to lower moisture loss in fries at 310 °F, resulting in reduced space for oil penetration into the surface.

Ultimately, the temperature at which we fry doesn’t significantly impact the oil content of our food. The essential takeaway is to ensure proper draining of the food, either on a wire rack or preferably on a paper towel to minimizes oil absorption.

Does oil freshness matter?

The degree of freshness in oil significantly influences its hydrophobic properties. As it’s widely known, oil and water exhibit an aversion to mingling, and this phenomenon is pivotal in the effectiveness of deep frying. Placing a food item into a vessel of hot oil results in minimal oil absorption, at least until a sufficient amount of moisture has been expelled from the food.

The progressive deterioration of oil leads to a reduction in its hydrophobic character. Initially, this can be advantageous. Oil with fewer hydrophobic molecules can have closer contact with foods, facilitating a slightly more efficient frying process. This is where the wisdom of those experienced tempura chefs becomes relevant—adding a small portion of aged, degraded fry oil to a new batch can enhance its performance.

However, as this degradation persists, the oil gradually loses its hydrophobic qualities, eventually infiltrating the food at an accelerated rate. This intrusion leads to an unwanted greasiness and the loss of the food’s crisp texture.

At this point, the oil requires replacement. Several telltale indications of aged oil include the presence of foam on the oil’s surface, an incapacity to attain frying temperatures without generating smoke, and a dark, unclean appearance accompanied by a musty, fishy scent.

How many times frying oil can be used?

When frying at home, the oil is more prone to degradation compared to frying in a restaurant setting. The reason behind this lies in the heating setup. In a professional restaurant-grade deep fryer, the heating components are elevated above the bottom of the oil reservoir. This design creates a zone of relatively cooler oil at the very bottom, positioned below the heating elements. Consequently, any tiny food remnants that detach during the frying process settle at the base of the chamber, beneath these heating elements.

Conversely, with a home arrangement, we typically employ a pot or a wok situated over a stovetop burner. Food particles descend to the bottom of the pan, making direct contact with the heat source, where they burn and infuse their flavor into the oil, expediting its deterioration.

How to Prolong the Oil’s Lifespan?

  1. Utilize a Thermometer! Overheating the oil represents a swift and straightforward technique for inducing its breakdown into an unsuitable state. Conversely, insufficiently heating the oil before adding food to it will extend the duration during which the food remains immersed. This, in turn, increases the likelihood of particles dislodging from the food, potentially shortening the oil’s lifespan.
  2. Maintain Cleanliness! Maintain a fine mesh strainer near your pot while frying food, and use it periodically to cleanse the oil by capturing and disposing of any fragments of batter or breading that may have separated from your food.
  3. Opt for Battered Foods or Uncoated Vegetables. Battered foods will introduce considerably fewer impurities to the oil compared to breaded or flour-coated foods. Uncoated items like French fries or sweet potato fries introduce even fewer impurities.

How to Clean Oil


  1. Employ a skimmer to eliminate any floating particles and large debris that may be lurking within the pot.
  2. Strain the oil through a fine mesh strainer into a clean, dry pot. Dispose the layer of soiled, flour-laden oil at the pot’s bottom, if any.
  3. Cover the pot containing the strained oil to shield it from dust and allow it to cool entirely.
  4. Pour the oil into a storage container then seal the container securely and store the oil in a cool, dry location.


  1. Employ a skimmer to eliminate any floating particles and large debris that may be lurking within the pot.
  2. Strain the oil through a kitchen towel lined mesh strainer into a clean, dry pot. This will take time and requires the oil to be hot which carries the risk of burn injuries. Dispose the layer of soiled, flour-laden oil at the pot’s bottom, if any.
  3. Cover the pot containing the strained oil to shield it from dust and allow it to cool entirely.
  4. Pour the oil into a storage container then seal the container securely and store the oil in a cool, dry location.


  1. After deep-frying, let the cooking fat reach room temperature or slightly warmer.
  2. In a small pot, measure half a cup of water for every quart of used oil. Sprinkle one teaspoon of powdered gelatin per half cup of water and allow the gelatin to hydrate for a few minutes.
  3. Heat the water until it simmers (this can be done on the stovetop or in the microwave), stirring until the gelatin dissolves. Stir vigorously and constantly, then pour the gelatin/water mixture into the soiled oil. The mixture should appear quite cloudy and reasonably uniform at this stage.
  4. Cover the pot and place it in the refrigerator (or transfer the mixture to a separate container before refrigeration) and allow it to rest overnight.
  5. The following day, pour the oil from the top of the pot or container into a separate clean, dry pot.
  6. Discard the gelatin disc that remains. The clarified oil is now ready for use.

When the clarified oil is used again it may start to produce slight bubbling. This is perfectly normal. Gently swirl the pan as it bubbles to aid in releasing any residual water droplets. It will eventually settle down and become suitable for frying.


  • Deep frying is cooking technique used to remove moisture from food.
  • The more moisture is removed the more oil is absorbed by the prepared food.
  • The amount of oil absorbed depends on the porousness of the food.
  • Frying temperature isn’t directly related to the amount of oil absorbed.
  • Despite common perception, sogginess is not the sign of oily food but the opposite.

Check out: All About Cooking Oil for more!

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