Method to Revolutionize Frying Technology
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Method to Revolutionize Frying Technology Proposed by: David Barron (907) 301‐6983 [email protected] Mechanical Engineering – The University of Texas at Austin This paper is submitted in response to the design challenge posted on MindSumo. It details the heat transfer process of frying foods and an alternative method to achieve the same heat transfer characteristics in order to cook foods from frozen which will have the classic fried food attributes (crispy, flaky, crunchy, etc.) after cooking. Additionally, a brief commercialization summary for the alternative method is outlined, as well as a comparison of the proposed alternative method to deep frying in terms of energy efficiency and safety. As a college student with a full load of classes and little to no cooking skills, frozen foods are not only a category of my diet, they are my diet. I have been through that jumble of brands and products in the freezer section, not just once but what seems like a thousand times; there really are no good options when I want a classic fried food in a short amount of time. In order to replicate the organoleptic properties fried foods, we really need to understand the mechanism which creates these different attributes. Interestingly, the oil in a deep fryer does not interact with the interior water molecules which keep the food moist; deep frying is therefore considered a dry cooking technique (Chan, 2007). The heat from the oil is transferred to the interior of the food via convection from the oil to the outer layer and conduction from the outer layer to the interior. The convection from the oil to the outer layer of food achieves an outrageously large convection heat transfer coefficient on the order of 800 ⁄^2∗ due to boiling the water in a thin layer on the exterior of the food and the high heat capacity of the oil (Farinu & Baik, 2007). Essentially, when the food is submersed in the hot oil, the water in a thin layer of the food is superheated and rapidly boils on the surface of the food. This outer layer is now devoid of water and at the temperature of the hot oil (450 to 465K), which leads to the crispy exterior of fried foods. The high convection heat transfer coefficient implies a large heat flux to the exterior of the food, which is then conducted to the interior of the food. The water in the interior of the food is trapped by the submersion in oil and due to the rapid cooking does not have time to migrate to the exterior where it would be superheated. Therefore, the high convection heat transfer coefficient yields a high heat flux into the food resulting in fast cooking, a moist interior, and the classic crispy and flaky exterior. Unfortunately, it is very hard to replicate this heat transfer using any other process. A microwave oven operating at the standard 2.45 GHz penetrates all sides of the food up to about 0.65”, such that any piece of food less than 1.3” thick will be fully penetrated by the radiation (Golio, 2003). The microwave frequency has been tuned to essentially create high frequency oscillations in the polar water molecules contained in the food. This process has the unfortunate effect of vaporizing some of the water in the food; the vaporized water then diffuses from the interior of the food, which has been pressurized due to the vaporization, to the outside of the food which is at a lower pressure. In this way, the microwave not only decreases the interior moisture content, but brings that water to the outside of the food leaving a soggy exterior. The only key advantage of the microwave is that the cooking time is extremely short since the radiation is penetrating the full volume of the food. Adjusting the power setting of the microwave essentially modulates the pulse width of how long the microwave is cycled on and off. Decreasing the power setting leads to slightly vaporizing the interior water molecules, but then letting them re‐condense as they transfer heat to the surrounding food molecules. Therefore, decreasing the power setting can help keep food moist, but increases the cooking time and still makes the exterior layer of the food soggy and moist. A standard conventional oven has different challenges in replicating the heat transfer process of frying. A conventional oven relies upon free convection to transfer the heat from the oven heating elements to the food; the convection heat transfer coefficient for this process is on the order of 5 to 25 ⁄^2∗ , an insignificant value compared to the deep fryer. The oven does not tend to remove a significant amount of moisture from the interior of the food and even creates a crispy exterior layer under the correct circumstances; unfortunately, a conventional oven can take exponentially more time to cook due to the paltry convection heat transfer coefficient. While convection ovens decrease cooking time by up to 25% by using forced convection, cooking times are still significantly longer than frying. In order to revolutionize frying technology, I propose to leverage the best aspects of both the microwave and the conventional oven by combining these processes and tweaking each process’s parameters. Several companies have introduced microwave ovens with a convection oven unit built in. While some of the end products are lacking in convection oven component, more and more of these types of products have a legitimate claim as both a microwave and convection oven, and the abundance of these products seems to be rapidly increasing due to high customer Figure 1: GE Convection/Microwave Oven appeal. For the purpose of this discussion the “Convection Over‐the‐Range Microwave Oven” (Figure 1) will be used as an example of good quality convection/microwave combination oven; this appliance combines 1000 watts of microwave power and 1550 watts of convection oven power in a single unit. Additionally, GE has already proven the ability to use both the convection oven and microwave simultaneously with their “FastBake” cooking feature. The user manual tends to describe the FastBake feature as a method to decrease cooking time, but only for foods which are intended for the oven, but do not call for the oven to be preheated (GE profile convection/microwave, 2011). I propose to use this combination of microwave and convection oven more like a microwave to cook frozen foods in order to replicate the heat transfer process of frying which will impart organoleptic properties to the food. The process would go as follows; after placing the frozen food into the convection microwave oven, the oven would immediately begin its somewhat slow heating cycle up to its maximum temperature while the microwave would begin to cook the food on a medium to low power setting. Keeping the microwave power setting fairly low will first thaw the frozen food, and then begin to heat the interior of the food in a fairly uniform manner. The power setting would be tuned such that as little moisture as possible is allowed to escape from the food. The oven temperature would help to cook the food without drying out the inside and beginning to develop a crispy exterior. Once the entire volume of the food is cooked, the microwave would be shutoff while the convection oven would remain on at its maximum temperature (450°F) for just enough to time to evaporate the moisture in the outer layer, drying that thin exterior layer to a crispy, flaky consistency while keeping the interior moist and cooking time low. This method could be easily implemented commercially through a partnership with GE (or any of the other manufacturers of this type of product) to help modify their appliance for frozen food to be cooked. The hardware necessary has already been developed and commercialized; an extra program for the appliance could be written with little cost in order to implement the heating procedure previously outlined. The appliance would be outputting tasty, crunchy, crispy, and flaky food without the cost of expensive hardware development making this technology easy to implement in both a consumer and commercial setting. Initial implementation could occur in a restaurant setting where health conscious restaurants can advertise and promote the healthy alternative to fried foods, while still delivering crunchy comfort foods to their customers. Widespread implementation would occur as these appliances became more widespread (which appears to be the current market trend). A food supplier could work closely with a microwave/convection oven manufacturer to create a specific brand of food and branded button on the appliance; in this way, once the consumer has purchased the appliance with branding they are constantly reminded that with the touch of a single button they could enjoy a delicious “fried” food if they buy the branded food in the freezer isle. The branded button would implement the aforementioned heating process while also serving as constant source of advertising in the kitchen. Clever brand management such as appealing to health oriented consumers as well as college students like me could increase sales even more. Another key advantage of this technology is that there are no associated safety hazards. Hot oil has the tendency to pop and sputter causing burns to the operator. In the microwave/convection oven with the new setting for crispy food from frozen, the food is entirely and safely confined in the appliance. The appliance would be safe enough for the average consumer to make crispy foods from frozen at home. Finally, as compared to a deep fryer, the microwave/convection oven with the new setting for crispy food from frozen would be more energy efficient.