This is your best bet for a smoked beef brisket mop. The mixture of oil, vinegar, and beer will keep the meat tender and flavorful during the smoking process. It is applied every two hours. Brisket gets its layers of flavor from building up the bark. The dry rub is a big part of developing the savory bark, and some cooks simply leave it at that, but some also use mops. Mops were originally used for open-pit barbecue where the meat was more likely to dry out during the long hours of smoking. A mop is a thin sauce that has a bit of acid and oil, like a marinade. It is applied lightly so as not to wash off any of the dry rub. While the use of mop sauce is hotly debated, it can add extra layers of flavor to the brisket. If you were cooking in a large open-pit barbecue, you might use an actual clean kitchen mop to apply the mop sauce. But for home use, look for a barbecue mop tool in the kitchen aisle. These look like miniature kitchen mops. Or, use a spritz bottle, which is even less likely to disturb the rub.
