Because cannabinoids themselves have a high boiling point and would foul or degrade when exposed to high temperatures vacuum is applied to lower the boiling points. If you are not able to achieve a deep enough level of vacuum whether through leaks, poor vacuum pump performance, or other ways the temperature needed for distillation to take place is increased. As temperature is increased the degradation of cannabinoids becomes increasingly greater. Generally, temperatures above 245°C lead to increasing degradation and this should serve as the upper limit for recommended temperatures to distill.
Temperatures higher than 245°C leads to an increase in cannabinoid degradation products like CBN, and especially delta-8-THC. At temperatures above 260°C more than 50% of cannabinoids can be converted to these degraded cannabinoids and other unknown compounds. If, however a heavy vacuum leak is in your system and is exposed to these temperatures a much heavier degradation will take place. A complete loss of cannabinoids is possible as they polymerize at high temperatures and exposed to oxygen. They will turn into a solid that is very hard to remove from the flask. In general oxygen should be limited as it will degrade the oils. Back-filling flasks, containers, and the complete distillation system with inert gas wherever possible is recommended.
Exposure to acids, light, metals, heat, and oxygen or oxidizers will cause degradation. Use of activated absorbents can also cause degradation if combined with the oil and exposed to high temperatures. It should go without mentioning that adding absorbents to the boiling flask and distilling with them will lead to heavy degradation. Depending on the level of activation, amount of absorbent used, and temperatures the level of degradation can vary. The absorbents work best at lower temperatures and any reduction in color associated is likely caused by the breakdown of compounds. Those that have added adsorbents to the boiling flask and distilled have noted a heavy blue fraction and this is likely an indication of the breakdown of cannabinoids.
Also noted is a conversion of cannabinoids into CBC. Oil begins to rapidly break down when exposed to air after this initial heavy degradation. A color change from colorless or yellow to pink or red after exposure to air indicates that the sample is oxidizing and the rate of which indicates the level of initial degradation, or put another way, the more degraded the sample the quicker it will oxidize after exposed to air. Samples that are heavily degraded can change from colorless to pink in less than 24 hrs. Cannabinoids have antioxidant properties and are initially somewhat resistant to chemical breakdown, but eventually they will degrade and once that process has begun it will accelerate. In order to attain an acceptable shelf life, potency, and consistency one must always seek to find method to limit or reduce breakdown and oxidation.
It also must be noted that in order to make clean distillate without any issues you must first winterize (de-wax) your sample.