Mum Taryn Ibell, who started the Facebook page, said she discovered the change after opening a new packet last week.
"It tasted disgusting. Like all malt and nothing else."
She said she used Milo as a way to encourage her daughter, who was born premature and was fed through a tube for two years, to drink milk.
"Now she won't touch the stuff," she said.
"Not many people understand this struggle and it's easy to say there are other ways of getting her to drink milk ... but if you haven't been in this situation you don't see how hard it can be.
"We stick to what we know works without the hassle of terrifying our kids backwards into non eating/drinking again. It's a daily struggle."
Many others also commented that their families weren't happy with the new taste.
Rachel Lee wrote: "With 3 teenage boys in the house we go through ALOT of Milo each week. My boys are not happy and I agree, the new recipe tastes awful! if it doesnt get changed back, I wont be buying it again!"
Another commenter said that her mother, who had been buying Milo since 1965, "had to go throw up in the toilet after tasting it".
One fan posted that packages with a best before date of August 2016 and later contained the new flavour, and some were buying up all the stocks of the old recipe they could find.
Darrell Sveistrup posted a photograph of 10 tins and six bags of Milo, saying: "Well that's all the milo in 3 stores around our house with old recipe. I think I have enough for about 1-2 weeks. Looked for one that says 6 vitamins and minerals. New one says 8 vitamins and minerals. I think one of two new minerals was dirt."
On the Milo Australia and New Zealand Facebook page, the company was also fielding angry complaints about the change.
In response to one complaint, the company said: "We've made a small change to our NZ recipe in order to focus on the four primary ingredients that make up MILO which are Milk Powder, Malt Barley, Sugar & Cocoa."
In response to another complaint, it explained: "We've just recently adjusted the vitamins and minerals in MILO so now it is delivering a balance of vitamins to really support energy production to help active kids, and adults, perform at their best. We've added vitamin D, B3, B6, B12 and taken out vitamin A, B1 and magnesium. Magnesium is naturally found in milk though so you'll still be getting some with every glass of Milo and Milk."
Nestle spokeswoman Margaret Stuart said there were no plans to change the formula despite the protest.
While she admitted there had been a slight shift in flavour, the drink's four main components remained the same.
"We understand that many people don't like changes being made to favourite products, so this change was not made lightly."
The changes were part of a global change to Milo, Ms Stuart said.
"[The changes] reflect our research into the nutritional needs of children.
"The key component is Vitamin D - recent research shows that kids nowadays are deficient in this vitamin, despite all the milk they drink. For this reason, we will not be changing the recipe."
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