Deep frying
Frying or baking is the roast related cooking method in which food in hot fat baked swimming. In contrast to roasting, when deep-frying the food is heated up over the entire surface , primarily through thermal conduction . This is comparable to cooking , but the significantly higher temperatures of 140 to 190 ° C result in a dry crust and aromatic roasting substances ( Maillard reaction ).
| product | Smoke point ° C |
|---|---|
| refined peanut oil | 230 |
| Palm kernel fat | 220 |
| Sunflower oil | 210-225 |
| Clarified butter | 205 |
| refined oils | > 200 |
| cold-pressed olive oil | 190 |
| cold-pressed rapeseed oil | 130-190 |
For deep-frying, suitable fat with a high smoke point , vegetable oil , lard or clarified butter is heated to just about the smoke point in a saucepan or a special deep fryer and the food is added. If the fat is not hot enough or cools down too much due to the addition of too large quantities of food, the pieces will be soaked up with fat before a crust can form. The rapid transfer of the highest possible temperature to the surface of the food to be cooked largely prevents it from penetrating, because the water vapor from the food, which develops due to the high temperature, then flows against the penetrating fat. This effect is even more pronounced in industrial vacuum fryers .
The water vapor on the surface of the fat level prevents oxygen from reaching the hot fat, which is why fat that is constantly used for the preparation of deep-fried food oxidizes more slowly than fat that is heated or kept warm without deep-fried food. On the other hand, water-rich foods ( French fries , meat dishes, etc.) lead to faster fat deterioration than less watery foods ( e.g. donuts ).
The temperature should not be too high, since at over 175 ° C the potentially harmful acrylamide can be increased. In the event of extreme overheating (> 200 ° C), the highly toxic acrolein can also be formed. Bioluminescent and histological studies on a mouse model of late-stage breast cancer showed that feeding thermally abused deep-frying oil (TMF) resulted in a significant increase in metastatic lung tumor formation compared to feeding fresh soybean oil. In addition, metastatic tumors in the lungs in animals consuming the TMF treatment diet showed a 1.4-fold increase in the Ki-67 marker for cell proliferation, and RNA sequencing analysis of liver tissue revealed a diet-induced modulation of gene expression in the liver . The thermally abused oil used in this study contained approximately 15 percent polar material (TPM VALUE); H. chemically modified triglycerides and fatty acids that are used as chemical markers for the breakdown of oils. Fresh oil contains 2-4 percent or less polar material. The maximum polar content determined by regulations in the countries of the EU is in the range between 16 and 27 (Germany 24) percent. This can be achieved in two to three days in a restaurant. When fats are heated, numerous decomposition products such as conjugated fatty acids , polymerized triglycerides and their breakdown products (free short-chain fatty acids , mono- and diglycerides , aldehydes , ketones , polymers, cyclic and aromatic compounds) are produced, which lower the smoke point, make the fat more viscous and can result in a soapy or scratchy taste. Strong overheating also increases the risk of a grease fire , which can cause severe scalding and cannot be extinguished with water. Spoiled deep-frying fat and the food prepared with it are harmful to health and not marketable. Placing such food on the market is a criminal offense.
From a chemical point of view, when fat spoils, the reactive double bonds of the long-chain unsaturated fatty acids oxidize and the long molecular chains break or polymerize.
Frying fat that is not overheated can be used several times as long as it is filtered to remove impurities that lower the smoke point and develop bitter substances. It should be noted, however, that the fat often takes on the taste of the food prepared in the first deep-frying process and this can be transferred to the food cooked in the second deep-frying process.
For frying are particularly suitable starch-rich foods such as potatoes and other solid vegetables , pastries too, but meat or fish , which to often breaded or batter is wrapped, as they themselves hardly contain carbohydrates. The pieces shouldn't be too big or as flat as possible so that they'll be cooked inside when the surface is browned. The surface should (apart from the batter) be as dry as possible so that the fat does not splash and cool down too much.
Web links
- Acrylamide: the known - and ignored risk . LifeGen.de
- Christian Gertz, Bertrand Matthäus: Optimal frying . (PDF) German Society for Fat Science
Individual evidence
- ^ A b Christian Gertz, Bertrand Matthäus: Optimal Frittieren . (PDF) German Society for Fat Science; accessed in June 2012.
- Jump up ↑ Anthony Cam et al .: Thermally Abused Frying Oil Potentiates Metastasis to Lung in a Murine Model of Late-Stage Breast Cancer. In: http://cancerpreventionresearch.aacrjournals.org . February 2019, accessed on March 23, 2019 .
- ↑ ROY, Glenn, M., Oakdale, PA 15071, US: EXTENDING THE LIFE OF EDIBLE OIL WITH ACTIVATED CARBONS. PatentDE, 1998, accessed in March 2019 : "The maximum polar content set by these regulations in the range between 16 and 27 percent can be achieved in two to three days of restaurant use."
- ↑ Hohenheim University: DETERMINATION OF THE POLAR COMPONENTS (TPM-W ERT). (PDF) uni-Hohenheim, 2009, p. 5 , accessed in March 2019 : “The content of polar substances is a reliable parameter to characterize the extent of fat spoilage during deep-frying. In Germany, a fat is considered spoiled if the limit value of 24% polar components (TPM value, total polar materials) is exceeded. In some other countries such as B. Austria or Switzerland values up to 27% are tolerated. "
- ↑ Gerhard Billek: we asked experts . ( Memento of the original from August 13, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Margarine Institute for Healthy Eating V.
