One of the group, who wanted to remain anonymous, believed the butter was dumped after Fonterra this week recalled two of its butter products, which were found to have metal objects in them.
Fonterra Brands managing director Peter McClure said the recall was a precaution, but products should not be consumed.
Customers were asked to return the product to where it was bought, with the appropriate packaging, for a full refund.
But, rather than let the butter be wasted the dumpster divers distributed it to anyone who wanted it, with a warning about the risk of eating the product.
"We have a very inefficient food production system that creates a lot of waste," the spokeswoman said.
"It's the sort of waste that would have horrified the [World War 2] generation, and which now horrifies my generation - an environmentally conscious generation."
Dunedin resident Joan McDonald (75) was delighted when she found one of the dumpster divers had put six packets of the product in her mailbox.
She said there was nothing wrong with it and she had already used about 500g to bake a batch of biscuits, a cake, some muffins and some pineapple tarts.
"It costs $6 a pound [453g]. Throwing it away is waste of the worst kind," she said.
"I had to stop baking because butter cost so much."
She was far from worried the butter had been retrieved from a supermarket skip, because it was being used solely for baking: "200degC will kill anything it catches in a dumpster".
"I think we should be given a choice about having access to it. If you let us buy it, people will buy it," she said.
The recall
Mainland Salted Butter 500g with a best-before date of January 10, 2013 (Batch CV12).
Anchor Salted Butter 500g with a best-before date of January 26, 2013 (Batch CV28).
