For SARS-CoV-2 and SARS-CoV1 this study published in NEJM by a NIAID team was done at a temperature of 21-23°C (see the Methods section in their supplemental material).

What's known about virus stability in general and for these two viruses specifically at much lower temperatures? (e.g. 4 °C, fridge temperature).

  • $\begingroup$ SE Biology is concerned with the mechanisms of biological processes. General information about the coronavirus is available from a variety of reputable sources, some of which are listed here. You are advised to consult them. $\endgroup$ – David Mar 27 '20 at 11:47