Basting is a practice so ingrained in the fabric of cooking poultry that most of us do it without question. We assume all that basting will make the bird juicier and more flavourful. However, according to Cook's Illustrated, you could probably just skip it.
To determine whether or not the time-honored practice greatly affected cooking time and moistness, Cook's Illustrated cooked three turkey breasts three different ways. All were roasted in 180-degree ovens but one was left completely undisturbed, one was basted every twenty minutes, and one was left unbasted, but the door of the oven was opened every twenty minutes.
The turkeys reached the target temperature of 70 degrees Celsius at different times, with the undisturbed bird cooking the fastest (59 minutes), and the basted turkey taking ten minutes longer. This slower cooking time is supposed to result in a juicier bird, but it didn't make that much of a difference. When Cook's Illustrated weighed the breasts before and after cooking to check for moisture loss, they found that all three lost a "comparable amount" of moisture (22.4 to 24.0 per cent) whether they were basted or not.
The only real difference basting made was visual; the basted turkey browned a bit more evenly and had a darker, shinier appearance. If you're a huge fan of dark, glossy poultry skin, baste away, but considering how much other prep goes into a roast dinner, returning to the oven every half hour to baste may be a step worth skipping.
Is Basting Really Worth It? [Cook's Illustrated]