He said farmers got about 60 cents per litre of milk sold.
A Foodstuffs spokesperson said retail prices took into account the wholesale cost from suppliers, which could change according to the price they could achieve on the global market.
"Then we add our own costs which include but are not limited to wages, salaries, transport, refrigeration, taxes etc," she said. "We aim to be competitive and try to ensure this fridge staple is as affordable as possible for New Zealand households."
Dr Lang referred to a recent trip to Europe and the shocking price comparisons on dairy products there.
In Germany for instance, he discovered that a litre of fresh milk was selling for the equivalent of $1.51, compared to $2.37 in New Zealand.
When the Herald looked at prices on Monday of a 2 litre bottle of milk at the big supermarket chains, the range was between $3.45 and $6.79.
Foodstuffs said economies of scale, population size, subsidies, different production methods, welfare standards, tariffs, wage rates and employment conditions, exchange rates and GST equivalents needed to be taken into account when looking at prices overseas.
The majority of shoppers told the Herald as they left Pak'nSave in Mt Albert, that milk was far too expensive.
Daniella Vega said it was becoming harder to afford.
"And I'm a Mum as well so I need to consume a lot of milk. I spend about $30 to $50 per week on milk."
Diana Strom said she bought the cheapest milk on offer, the Fonterra-owned Dairy Dale brand.
Others like Holly Mills, have made switches between types of milk purely on price.
"Trim is probably the cheapest I think. I used to buy Calci-trim for more calcium but it's really expensive. It's about $5 I think."
Some other shoppers thought the price "is what it is", didn't buy milk or preferred plant milk alternatives.
Angela Doran said the issue wasn't just about milk at all.
"I've just been overseas and their milk is much cheaper, as are all of their groceries."
Helen Paddon however reminisced about the "good old days".
"I'd like to go back to how it used to be when I was a kid, and they would drink the milk straight out of a cow."