You very much can use it to pasteurize! This is the least effective way with the most unpredictable results to try to 'sterilize.' In order to sterilize a substrate, you need temperatures higher than 250°F (121°C) (varies by altitude) for a minimum of 2 hours. Increasing the heat does not increase the temperature of boiling water (212° F) any further. You'll need to add pressure to raise the temperature to 250°F (121°C) or above to kill off bacteria and fungal spores. Most mushroom growers will need 15 PSI of pressure to increase the temperature of the steam to 250°F (121°C). An autoclave or pressure cooker are commonly used to achieve sterilization.