I play around with sun rendering certain items (Fat, Egg, BTO, etc) but I have never added anything to preserve them. If I have a large batch that will take me a few years to get through, should I be adding sodium benzoate to keep them from going rancid? Thanks.

Clean well handled sun rendered oils in general should not need any preservatives or mold retardants. Some lard condition type fats may develop mold or can sour somewhat depending upon how clean the fat was from any tissue or blood. Also if the container used for storage was relatively clean prior to its use.

Good clean rendered fat and grease type materials can last if kept at room temperature for many.... years. A spraying of the top of the material and the inside walls and lid of the container with a Methyl Paraben solution will stop any mold development. I always check storage materials periodically to make sure they don't need any attention.

Expanding containers, lids or discoloration that is noticed in glass or transparent containers should be examined for any changes in the material that could adversely affect product quality or possible material decline or decay.

Egg is prone to breakdown over time and mold development if nothing is added to preserve it and guard against mold growth. We culture our egg for use and hold many buckets on inventory for a few years between batches. Therefore preserving and guarding against mold growth is critical for long term storage. With our process we can hold egg indefinitely in pristine cultured condition.

These are all the precautions that we take in a commercial operation. When we work up large volumes of materials some may sit for years without immediate use. Therefore preventive measures need to be taken to ensure the quality of your ingredients or that a product will hold until it is needed for use.