There are several terms that are important when discussing cold-weather biodiesel. 

Cloud point, as the name suggests, is the temperature where the fuel becomes cloudy.  Microcrystals are beginning to form here.  The crystals are waxes.  In biodiesel fuel, it is biowax, in diesel it is paraffin wax.  When the crystals get large enough they settle to the bottom of the tank.

The fuel will become cloudier and thicker as the temperature is lowered, until the gel point is reached.  Filter clogging becomes a problem between the cloud and gel points.

Gel point is the temperature at which the fuel freezes solid and can no longer be pumped or poured.

As the fuel is warmed up, enough of it will melt so that it can be poured again- this is the ungel point.  However, many of the waxes will remain in solid form.  It can look like crystals, pellets, or amorphous goo.  Most of this wax will be loosely packed at the bottom of the barrel.  In order to completely remelt or redissolve the waxes, the fuel has to be warmed up to the remix temperature.  The other option is to only use the liquid fuel from the top of the barrel.  We have a winter buyback program for the wax-enriched bottom layer.

Below we have provided schematics of biodiesel made from virgin vegetable oil (top) and waste vegetable oil (our product- bottom).  Our product is shifted about 10 degrees warmer than the virgin product.  To combat this issue, we offer filter heaters that keep the fuel filters above the remix temperature and antigel additives that lower the gel  point (but not necessarily the cloud point).  For comparison, 100% diesel fuel has a cloud point around 20 F and a gel point around 0 F.