  We present a new calculation of the neutrino flux received at Earth from a
massive star in the $\sim 24$ hours of evolution prior to its explosion as a
supernova (presupernova). Using the stellar evolution code MESA, the neutrino
emissivity in each flavor is calculated at many radial zones and time steps. In
addition to thermal processes, neutrino production via beta processes is
modeled in detail, using a network of 204 isotopes. We find that the total
produced $\nu_{e}$ flux has a high energy spectrum tail, at $E \gtrsim 3 - 4$
MeV, which is mostly due to decay and electron capture on isotopes with $A = 50
- 60$. In a tentative window of observability of $E \gtrsim 0.5$ MeV and $t <
2$ hours pre-collapse, the contribution of beta processes to the $\nu_{e}$ flux
is at the level of $\sim90\%$ . For a star at $D=1$ kpc distance, a 17 kt
liquid scintillator detector would typically observe several tens of events
from a presupernova, of which up to $\sim 30\%$ due to beta processes. These
processes dominate the signal at a liquid argon detector, thus greatly
enhancing its sensitivity to a presupernova.
