Biol 106 the Science of Steak Health, Environmental, and Ethical
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Food and Science Laboratory – Biol 106 The science of steak Health, environmental, and ethical concerns aside, many people like to eat a good steak every once in awhile. The sustainability of steak (meat) eating is currently an area of concern. Clearly a good steak is something we probably should not take for granted. Chefs often refer to the need to respect the meat, i.e. don’t cook it poorly so that it is wasted. Beef steak flavor is distinctive and different than poultry, pork, and game. The ruminant digestive system of cows involves bacteria that break down cellulose, but the bacteria also convert unsaturated fatty acids from plant material into saturated fatty acids. Consequently, beef has a lot of saturated fat which is considered to be unhealthy. The saturated fat also contributes to the “cow-ey” “buttery” flavor of beef. Other compounds such as terpenes can come from eating grass and affect flavor (I personally do not prefer “grassy” beef). Ideally, the perfect steak should be flavorful, moist, and tender. The scientific method of cooking a steak attempts to maximize flavor, moisture, and tenderization. Moisture – A steak that is not dried out is more flavorful in part because soluble compounds that are rich in flavors can coat the tongue and are volatilized for aroma. Most cuts of meat have been processed in which the cut is perpendicular to the direction of the muscle fibers. This makes it easier to break the meat down by chewing, but since every muscle fiber is essentially open at the surface of the steak, the cytoplasmic contents which are the liquid in meat can leak out of the cut surface. This is exacerbated by the fact that the collagen sheath surrounding each muscle fiber will contract to some extent with heating, further forcing the cytoplasm out of the muscle cells. There is a popular myth that searing the steak on both sides using high temperature will “seal in the juices”. This is untrue because liquids and water vapor can both penetrate the carbonized surface of the seared steak. It is an unavoidable fact that a certain percentage of liquid will be lost during cooking. The actual purpose of searing is to create chemical reactions on the surface of the meat that are called browning or “Maillard” reactions. The caramelized sugars and amino acids facilitate the chemical alteration of other organic compounds of the meat giving rise to a complex mixture of flavorful and aromatic compounds. One way to maintain a high moisture content in cooking is to baste the steak with liquid, which evaporates instead of the meat juices, or by increasing the starting water content of the steak. If the starting water content is higher, and the same percentage of water is lost during cooking, the end result is a steak with higher moisture content. Brining to increase the moisture content of the steak – By soaking the steak for 48 hours in a 3-6% salt solution, sodium and chloride ions will diffuse into the steak due to the higher concentration outside compared with inside the steak. A 6% solution of sodium chloride (60 grams per liter) has an osmolarity of about 2000 milliosmoles per liter; steak has an internal osmolarity of about 300 millimoles of solute per liter. The ions will disrupt the interactions between actin and myosin, and at higher concentrations, will start breaking down actin and myosin directly. The brine treated steak has a greater ability to absorb water, so with sufficient time in the brine solution, the steak will take up more water. Flavor and tenderization – Meat becomes more tender during cooking due to the melting of fat layers and the breakdown of the muscle proteins (e.g., actin and myosin) as well as collagen connective tissue. Melting of fat layers is generally easily accomplished in cooking simply by raising the temperature. Cuts of meat that are from muscle that is not exercised, i.e., back muscle (tenderloin) are the most tender and have more fat between the muscle fibers (marbling). Exercised meats such as leg and shoulder have less fat between the muscle fibers, more connective tissue, and are less tender. Muscle proteins and collagen can be broken down over time, particularly if they are heated. When they break down, the meat is mechanically less tough. In addition, the breakdown of these molecules releases their component amino acids which can include flavorful compounds such as glutamate and glycine. Therefore, the longer the steak can be kept at a moderately high temperature, the greater the tenderness and the greater the flavor. However, the longer a steak is cooked, the more water will be lost. How then do you increase the breakdown of proteins? We will pre-warm our brined steaks by immersing them in warm water before cooking. This will raise the temperature of the meat so that the inside of the steak will rise to temperatures that promote protein breakdown more quickly and as a result, in theory, the steak will be more tender and flavorful. Lab Exercise – Scientific steak cooking 1. On the Tuesday before the Thursday cooking lab, prepare 2 roughly identical steaks as follows: a. Experimental steak – Weigh steak in ziplock bag. Label the bag. Be sure to put your name(s) and lab section on the bag and mark it as “Experimental”. Add about 500 ml of brine solution (240 grams per liter of drinking water) b. Control steak – Weigh steak in bag, then label bag. c. Place both steaks in basins marked “afternoon” or “evening” in the refrigerator 2. Before Thursday lab, instructors will remove experimental steaks and get rid of the brine and place the bags containing steak in a basin of warm tap water for 30-60 minutes. 3. Immediately before cooking, blot excess brine from the experimental and control steaks and weigh. Place a toothpick into the experimental steak to use for identification. Sprinkle salt onto both sides of the control steak. Weight of steak (g) Brining Cooking Tuesday Thursday After cooking % gain % lost Experimental Control 4. Place temperature probes into both steaks and place on the hot part of the grill 5. Record temperature at regular intervals. Sear each side of the steaks on hot part of the grill. 6. Once both sides are seared, move the experimental steak to the cooler part of the grill. Keep the control steak on the hot part of the grill. Cook each steak to an internal temperature of 55 degrees Celsius or higher (see guide for “doneness” below). 7. Let the steaks rest for several minutes after removing from the grill. Conduct blind taste tests to determine whether the experimental steak is more tender and flavorful. Temperature Doneness Meat qualities Actin/Myosin Collagen Protein bound Myoglobin Water 100 F/40 C raw soft to touch beginning intact begins to normal Slick smooth to unfold escape 120 F/50 C rare firmer begin to intact increase normal Opaque denature escape 130 F/55 C medium resilient coagulated intact Rare fibrous 140 F/60 C medium shrinking denaturing shrinking increased denaturing Exudes juice actin others squeezing flow Red to pink 150 F/65 C medium well shrinking Less juice Pink fades 160 F/70 C well more shrink dissolving ceasing coagulated Stiff Little juice Gray brown 170 F/75 C stiff Dry Gray brown Graph time vs. temperature of experimental and control steaks above. Fruit and Vegetable Classification Key Materials Various edible plant parts dissected for display Procedure Examine an available edible plant part and follow the key by deciding whether it DOES or DOES NOT each consecutive statement provided in the outline. If it doesn’t , move down the outline to the next statement of the same heading type. If it does meet the description, follow the more detailed notes in that heading to find a precise classification for the fruit. I. Fruit: a plant part specialized to produce and/or contain seeds 1. Simple Fruit – fruit formed from one ovary, and that ovary becomes fleshy or thick a. Dry Fruit – the pericarp becomes dry as the fruit matures/ripens i. Dehiscent Fruit – splits open at maturity by natural means, releasing their seeds ii. Indehiscent Fruit – does not split open when mature; most have only a single seed b. Fleshy Fruit – the pericarp, or at least part of the pericarp, becomes increasingly soft and fleshy as the fruit matures/ripens i. Drupe – a one-seeded fruit derived from a superior ovary; the endocarp becomes hard and “stony,” the exocarp is relatively thin, sometimes “hairy,” and the mesocarp is very fleshy or fibrous ii. Berry – typically a multi-seeded fruit in which the majority of the pericarp is fleshy 1. Hesperidium – a berry with a leathery rind and a nearly fluid-filled interior; several internal chambers may be distinguishable as divided by thin septa, or may all appear to blend together as a solid mass 2. Pepo – a berry with a more hard rind; some incomplete division of the interior space may be visible by incomplete septa, but often the inside of the pericarp is largely “hollow” iii. Pome – a multi-seeded fruit in which those seeds are encased in several separated, hollow chambers. Although these non-fleshy chambers are the pericarp, all are instead enclosed by an enlarged, fleshy receptacle 2. Accessory Fruit – may have smaller parts that can be individually keyed as simple fruits, but the fleshy/thick part is built out of some plant tissue other than the ovary 3. Aggregate Fruits – fruit formed from one flower that has multiple ovaries ; these ovaries fuse together, and result in a fruit that looks like many small fruits fused together 4.