Experienced cooks often share the secret of allowing braised dishes to cool down mid-way through cooking. This "resting fire" technique results in richer flavors, a subtle sweetness, and an appealing color. For example, the famed braised fish of Vu Dai village is not cooked continuously but is allowed to cool for several hours before resuming the braising process. Similarly, in Hue, braised meat and bamboo shoots are prepared with this "resting fire" method. This technique not only saves fuel (by utilizing the residual heat of clay pots or cast iron) but also enhances the overall flavor of the dish.

Northern-style braised fish with green banana. Photo: Bui Thuy

Food science explains that when ingredients are heated, proteins contract, expelling water and dissolved molecules like salt, sugar, and amino acids. Continuous heating evaporates these nutrients, resulting in dry, tough meat or fish. Turning off the heat and allowing the dish to cool reverses this process. The muscle tissues relax, and the change in osmotic pressure causes the braising liquid and seasonings to be reabsorbed, permeating the meat or fish.

When the heat is reapplied, this process repeats, building layers of flavor. The resting period also allows certain enzymes, active at moderate temperatures, to further break down connective tissues, tenderizing the meat without compromising its structure. Notably, at the initial cooling temperature (70-90°C), the Maillard reaction continues slowly, deepening the color and aroma.

Another often overlooked aspect is the stability of the braising liquid as an emulsion of fat and seasoned water. Vigorous boiling can cause the fat from the meat or fish skin to separate. However, during the cooling period, newly formed gelatin and peptides in fish sauce act as natural surfactants, improving emulsification and creating a smooth, glossy texture.

At this lower temperature, adding aromatics after the heat has been reduced allows the remaining active enzymes to further tenderize the surface tissues. The combined effect of these scientific principles – the cycle of pressure adjustment and diffusion, collagen tenderization, controlled evaporation to preserve aroma, and emulsion stabilization – results in a rich, glossy braise.

The "resting fire" rhythm varies depending on the ingredients and the dish. For braising fish, especially meaty varieties like carp, basa, or mackerel, simmer the fish with the seasoning liquid briefly before adding enough hot water to barely cover the surface and continue simmering for 15-20 minutes. Then, turn off the heat completely, cover tightly, and let the fish cook further in the residual heat. Once cooled, reheat gently, then let it rest again.

For braised meat, particularly pork belly, the alternating layers of fat and lean meat require time to meld. A common Northern Vietnamese method involves simmering the meat, turning off the heat for several tens of minutes, then reheating. Repeating this process several times yields a beautiful caramel color, a rich sauce, and a deep, savory flavor.

The resting period is crucial for Southern-style braised pork with eggs. Eggs become tough if boiled for too long, with the yolks turning dry and crumbly. Experienced cooks add the eggs after the meat has softened, simmer briefly, and then allow the dish to rest, ensuring the eggs absorb the flavor while remaining tender.

For drier braises like kho quet (a Southern Vietnamese dipping sauce), the "resting fire" method prevents the sugar and fish sauce from burning. Once the sauce thickens, remove it from the heat, let it cool, and then reheat. This prevents the formation of bitter compounds, preserving the sweet caramel flavor.

The ideal time to implement the "resting fire" technique is when the dish exhibits two signs: the ingredients are slightly firm and turning golden brown, and the braising liquid is beginning to thicken but has not yet reduced significantly. Resting too early prevents the flavors from melding, while resting too late can result in a breakdown of the ingredients' texture. The resting time depends on the specific dish and the thickness of the ingredients.

Whether using an induction cooker, gas stove, or electric pot, the "resting fire" technique remains applicable. Simply bring the dish to the desired simmer, turn off the heat completely, cover tightly, let it rest, and then reheat gently. With an electric pot, the "keep warm" setting can be used to maintain residual heat without boiling. Some professional chefs even employ a "double rest" or "triple rest" to mimic the rhythm of traditional charcoal stoves.

Bui Thuy