  How and when in the star formation sequence do dust grains start to grow into
pebbles is a cornerstone question to both star and planet formation. We compute
the polarized radiative transfer from a model solar-type protostellar core,
using the POLARIS code, aligning the dust grains with the local magnetic field,
following the radiative torques (RATs) theory. We test the dependency of the
resulting dust polarized emission with the maximum grain size of the dust size
distribution at the envelope scale, from amax = 1 micron to 50 micron. Our work
shows that, in the framework of RAT alignment, large dust grains are required
to produce polarized dust emission at levels similar to those currently
observed in solar-type protostellar envelopes at millimeter wavelengths.
Considering the current theoretical dificulties to align a large fraction of
small ISM-like grains in the conditions typical of protostellar envelopes, our
results suggest that grain growth (typically > 10 micron) might have already
significantly progressed at scales 100-1000 au in the youngest objects,
observed less than 10^5 years after the onset of collapse. Observations of dust
polarized emission might open a new avenue to explore dust pristine properties
and describe, for example, the initial conditions for the formation of
planetesimals.
