  We study Beltrami flows in the setting of weak solution to the stationary
Euler equations in $\Bbb R^3$. For this weak Beltrami flow we prove the
regularity and the Liouville property. In particular, we show that if
tangential part of the velocity has certain decay property at infinity, then
the solution becomes trivial. This decay condition of of the velocity is weaker
than the previously known sufficient conditions for the Liouville property of
the Betrami flows. For the proof we establish a mean value formula and other
various formula for the tangential and the normal components of the weak
solutions to the stationary Euler equations.
