Milk is a valuable resource that is gained along with Achievements.
It is used along with some upgrades to increase cookie output and is gained at the rate of 4% per Achievement, excluding Shadow Achievements. As of version 1.0465, the total number of Achievements that count towards milk is 157 and the maximum attainable Milk amount is 628%.
Kitten Upgrades (Kitten helpers, Kitten workers, Kitten engineers, Kitten overseers, and Kitten managers) increase cookie production based on the Milk percentage. As the Milk percentage increases it gains different names, although this does not change its effects on cookie production.
The cookie can also be dunked in the milk by zooming your browser in to roughly 200%, or resizing your browser window, earning you the Cookie-dunker achievement.
Below 100%, the Milk is plain white. When the Milk reaches 100%, it turns into chocolate Milk, with the color turning brown. As it reaches 200%, it becomes Raspberry Milk, giving the Milk a pink color. At 300%, it is orange juice and is colored orange. As it reaches 400%, it becomes Caramel Milk.
Below are five images the game uses to overlay the lower background.
TIP: The more milk you have, the more CpS the Kitten upgrades from the shop will get you.
At 52% Milk, you may unlock the Kitten helpers upgrade for 9,000,000 cookies. At 100% Milk, you may unlock the Kitten workers upgrade for 9,000,000,000 cookies. At 200% Milk, you may unlock the Kitten engineers upgrade for 90,000,000,000,000 cookies. At 300% Milk, you may unlock the Kitten overseers upgrade for 90,000,000,000,000,000 cookies. At 400% Milk, you may unlock the Kitten managers upgrade for 900,000,000,000,000,000,000 cookies.
With Kitten helpers, you gain 5% of your Milk percentage as more cookies, stacked multiplicatively with cookie upgrades. If you had 100% Milk, Kitten helpers, and 2 cookie upgrades 5% each, your multiplier would be 115.5%
With Kitten workers, another 10% of your Milk is added to your multiplier. This is stacked multiplicatively with Kitten helpers as well as cookie upgrades.
Kitten engineers adds another 20% of your Milk into your multiplier. This is stacked multiplicatively with cookie upgrades as well as previous Kitten upgrades.
Kitten overseers adds yet another 20% of your Milk into your multiplier. Same rules as before.
Finally, Kitten managers adds yet another 20% of your Milk into your multiplier. Same rules as before. See CpS for details of the calculation.
Let's add several cookie upgrades 150% total, 300% milk and all five kittens: (665%+150%)*(100%+300%*5%) *(100%+300%*10%)*(100%+300%*20%)*(100%+300%*20%)=(665%+150%)*1.15*1.30*1.60*1.60*1.60=3743.0016%
Santa's Milk and CookiesEdit
The Santa's Milk and Cookies upgrade makes "Milk 5% more powerful". This is a final (additional) 5% bonus. It does NOT affect the individual kitten multipliers.