Context : Complex organic molecules have been detected in massive hot cores for over two decades , and only recently in three hot corinos ( the inner regions surrounding Sun-like protostars , where the dust temperature exceeds 100 K ) .
Since hot corinos have sizes of \sim 100 AU ( i.e. , of the order of the extent of the Solar System ) , it is particularly relevant to understand whether they are common and to identify the formation route ( s ) of complex organic molecules .
Much has yet to be learned on this topic , since even recent models predicted it was not possible to form these molecules in low-mass protostars .

Aims : We aim to enlarge the number of known hot corinos and carry out a first comparative study with hot cores .
The ultimate goal is to understand whether complex organic molecules form in the gas phase or on grain surfaces , and what the possible key parameters are .

Methods : We observed millimeter rotational transitions of HCOOH , { HCOOCH _ { 3 } } { CH _ { 3 } OCH _ { 3 } } { CH _ { 3 } CN } and { C _ { 2 } H _ { 5 } CN } in a sample of low-mass protostars with the IRAM-30m .
Using the rotational diagram method coupled with the information about the sources ’ structure , we calculate the abundances of the observed molecules .
To interpret these abundances , we review the proposed formation processes of the above molecules .

Results : We report the detection of { HCOOCH _ { 3 } } and/or { CH _ { 3 } CN } towards NGC1333-IRAS4B and NGC1333-IRAS2A .
We find that abundance ratios of O-bearing molecules to methanol or formaldehyde in hot corinos are comparable and about unity , and are relatively ( depending on how the ratios are determined ) higher than those in hot cores and in Galactic center clouds .

Conclusions : So far , complex organic molecules were detected in all the hot corinos where they were searched for , suggesting that it is a common phase for low-mass protostars .
While some evidence points to grain-surface synthesis ( either in the cold or warm-up phase ) of these molecules ( in particular for HCOOH and { HCOOCH _ { 3 } } ) , the present data do not allow us to disregard gas-phase formation .
More observational , laboratory , and theoretical studies are required to improve our understanding of hot corinos .