The big benefit is clearly to the elimination of packaging waste going to garbage and recycling. Hopefully the end user is either self-composting or using a municipal collection program for the spent grounds. Grounds make a great soil additive, and does not need composting for this purpose.
-lack of a suitable labeling method, both for consumer product labeling, branding, and adding changing product data, for example as the coffee beans change.
-although there is no solid waste, the jars must be washed and sterilized prior to re-use. This requires detergent, heat and water consumption and the resulting effluent.
-coffee in jars is both bulkier and heavier than in flexible packaging (bags), needing more space in the delivery truck and more fuel use (CO2 production). The jars must be returned for re-use, generating more CO2. Also, if the jars are not returned, we have to assume they are becoming part of the waste stream in one way or another.
-consumers do not take up coffee purchases in jars as readily as bagged coffee. The reasons for this are not clear to me.
We are currently packaging retail coffee in 400g, 3 ply bags. These bags are light in weight, ship to us flat packed, and have a one way valve and a zip lock seal to protect the coffee from oxidation and loss of aroma as much as practical. It provides a nice area for labeling. I wish the bags were recyclable, but I am told by our local recycling authority that the technology does not yet exist to deal with plastic bags. Compostable bags do not provide adequate oxygen barrier for shelf life, at this time.
If you have any comments or suggestions for more sustainable coffee packaging, I would love to hear them.