The beta conformer is the second of the two "chair conformers" that exist in water. The population of beta is much larger than that of alpha. The important difference in these two sugars is that the methoxy group is equatorial to the ring. It is often assumed that steric interference is the determining factor in the ratio of alpha/beta anomers. Highlight the equatorial group and notice where it is in relation to the other groups.

Wire Frame: Ring O red; Anomeric O (C1) green

Oxygen in Green

Dot surface and Wireframe