To quantify if the INS concentrations were higher in the presence of 1% v/v OptiPrep™, we calculated the percentage of ice nucleation activity from the unprocessed suspension that was "recovered" after the addition of 1% v/v OptiPrep™ using the following equation: For K-feldspar, the average recovery of ice nucleation activity in suspensions with 1% v/v OptiPrep™ added was 94% (median = 87%, 25 th -75 th percentile = 51% to 116%) (Figure ), further suggesting that the freezing properties of K-feldspar were not impacted by the addition of 1% v/v OptiPrep™. For Snomax, the average recovery of ice nucleation activity in suspensions with OptiPrep™ was 409% (median = 294%, 25 th -75 th percentile = 206% to 520%). The recoveries suggest that the OptiPrep™ enhances the ice nucleation efficiency of Snomax by a factor of approximately 2 to 5 (Figure ). However, this increase in INS concentration corresponds to just a 0.3 °C difference in median freezing temperatures between Snomax suspensions with and without OptiPrep™, which is close to the uncertainty of our cold stage measurements (±0.25 °C). In addition, the 1% v/v is an upper limit to the OptiPrep™ concentrations likely to be present in the experimental isolates. As such, the observed enhancement of ice nucleation by Snomax in the presence of 1% v/v OptiPrep™ is an upper limit to the effect of OptiPrep™ on Snomax ice nucleation in our experiments.