It’s typical for brewing applications to use about 33-50% glycol to water. While 33% will technically work, it's right on the cusp of what will or won't work.  If your measuring is a little off or if condensation collects overtime (watering the glycol down) you could end up with a mix that still freezes. It's our recommendation to use a 50/50 mix, this provides plenty of buffer and is simple to measure accurately.