“Gravy Day” is a recently established event in Australia. It is inspired by Paul Kelly’s song “How to Make Gravy,” which tells the story of a prisoner named Joe who writes to his brother on December 21. Joe expresses his sadness about missing the family Christmas celebrations and wonders who will make the gravy for the roast lunch in his absence.
Although a roast may not be everyone’s preferred Christmas meal, “Gravy Day” provides an opportunity to explore the chemistry behind making gravy. Gravy is a thickened sauce made from the drippings collected from roasted meats.
When meat is roasted, it undergoes various chemical reactions that produce numerous new flavor compounds. Over 1,000 flavor compounds have been identified in roasted meats. Each chemical contributes unique characteristics to the taste and smell of the finished roast. For example, the chemical 12-methyltridecanal gives roast beef its distinct “beefy” flavor, while the sulfur-containing compound 2-methyl-3-furanthiol is often found in roast chicken.
There are three main types of chemical reactions that occur when roasting meats, resulting in the production of flavor compounds. The Maillard reaction, which involves amino acids from the protein reacting with sugars and simple carbohydrates in the meat, is responsible for both color and flavor. This reaction is also responsible for the flavors of roasted coffee, chocolate, steak, toast, and more.
Another reaction that takes place in a hot oven is the breakdown of fats through “lipid degradation.” This process creates hundreds of different chemical compounds, many of which have “fatty” or fried food-like aromas. The specific fat profiles found in different animals contribute to the profile of flavor chemicals that form during roasting.
The third type of reaction occurs when products of Maillard reactions and lipid degradation combine, resulting in additional flavor compounds. One such compound, known as 3-mercapto-2-methylpentan-1-ol, contributes a “gravy aroma” and comes from roasted vegetables. Including vegetables in the roasting pan adds depth to the flavor of the gravy.
During the roasting process, the fats separate from the meat and collect in the tray with the flavorful meat juices. While both the fat and water carry flavor compounds, too much fat can give the gravy an unpleasant texture or cause it to separate into layers when served. To control the amount of fat added to the gravy, it is recommended to pour off the pan juices into a jug and allow the fat to separate from the liquid. The excess fat should be disposed of responsibly and not poured down the drain.
The secret ingredient for a good gravy is flour or starch. Starches are complex chemicals made up of sugars joined together. When starch granules absorb water, they swell and form a gel-like network that thickens the gravy by trapping water and oil. Wheat flour is commonly used as the starch source, but corn and arrowroot starch can also be used. These alternatives have a higher percentage of starch and a more neutral flavor.
Salt is often used when preparing roast meats to draw out moisture and enhance flavor. The pan juices are concentrated during the gravy-making process, so it is important to taste the gravy before seasoning it with salt, as heating intensifies its flavor. Additional flavor components can be added to the gravy through ingredients like red wine, sherry, stock, or tomato sauce. These ingredients contribute sweetness, acidity, and umami flavors.
For those who prefer convenience or have made a mistake with their homemade gravy, instant gravy powder can be used. These powders typically contain maltodextrin or another corn-derived starch as the main ingredient. They also contain powdered fats, salt, colors, and various flavor additives. Instant gravy offers speed and uniformity due to controlled commercial production.
Unlike Joe’s concerns about his family’s gravy, instant gravy is more likely to taste the same regardless of who prepares it.