When a reader recently shared that she experienced a whoosh of flame when opening her oven door while preparing a Milk Street recipe, we were more than curious. She was preparing Portuguese-Style Pot-Roasted Chicken, which calls for braising the meat uncovered in tomatoes and 1 cup of port or brandy at 400°F for 50 minutes. The flames occurred when she opened the oven door after 30 minutes.

This did not happen during our original recipe development, so we went back into the kitchen and made the recipe eight times. We were not able to replicate the reader’s experience when we used port. And as long as we allowed the dish to cook for the full 50 minutes, we couldn’t replicate it with brandy, either. We did test opening the oven door after 30 minutes on two separate occasions with brandy; one time we did get some flaming and the other time nothing happened. Our advice? Stick with port, which has about half the alcohol as brandy. Also, allow the dish to cook for the full 50 minutes so any vapors can dissipate.

To sort out why this happened, our science advisor offered the following explanation. Though lower-alcohol options such as wine and port are more difficult to set alight than higher-proof alcohols such as brandy (we have heard of wine igniting, too), technically any alcohol can ignite under the right conditions. For that to happen, three things are needed: a concentration of alcohol vapors between 3.3 percent and 19 percent by volume of air; a source of oxygen; and an ignition source (such as a hot coil in an oven).

When alcohol is heated in an oven, as in our recipe, the alcohol evaporates and forms combustable vapors. But most modern ovens are vented, which means those vapors typically don’t get a chance to concentrate to a point where they can ignite. Further complicating things, our reader said her pot had particularly high sides, bringing its rim within a few inches of the roof of the oven. This created a pocket where those vapors could concentrate. When the oven was opened early, oxygen rushed in, creating more favorable conditions for ignition. So a shallower pan is less likely to create these conditions than a taller one. Also, a covered pot would also concentrate alcohol vapors which, if the pot were opened in the oven, might indeed provide the conditions necessary for combustion.

Two years ago, we got an email from a reader who was roasting a leg of lamb in a full bottle of red wine. After two hours, the oven door exploded open with flames. That’s because alcohol boils at a lower temperature than water (173°F versus 212°F). As the alcohol simmered, the vapors slowly escaped the Dutch oven, rising to the top of the oven. Once the alcohol vapors reached a sufficient concentration, they ignited the next time the heating element came on.

So if you are baking or roasting with a significant amount of alcohol, even wine, we suggest using a shallow uncovered pan and not opening the oven door until the dish is fully cooked so that any vapors will have time to dissipate.

Have you had similar experiences? We’d love to hear.

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