My wife is in the habit of making ice cream easier to serve up by defrosting it in the microwave for 20 seconds or so to soften it. After serving, the ice cream goes back in the freezer until the next time.
I estimate that a 2 litre tub of ice cream may well be microwaved and then re-frozen 6-8 times.
Is it safe to do this? Is it safer, or less safe, than just letting the ice cream defrost at room temperature for half an hour?