Where does all the milk go?
How one white liquid branches into 50+ commercial products
In late 2024 I was shopping for milk when I started wondering how many cows -- or how many days -- it would take to produce my 1.5L bottle. I looked it up and found that the most productive dairy cows can yield fifty litres per day at their peak. Which means my bottle took roughly 43 minutes to produce. 43 minutes!!
My first reaction was that milk must be absurdly overpriced. If one cow can produce fifty litres a day, how is supply ever a problem? But that question quickly got overtaken by a different one. I was standing in the dairy aisle looking at the yoghurt, the cheese, the butter, the cream, the condensed milk, the powder, the ghee.. and it hit me -- hold on. This is all from milk? ALL of it? The same white liquid? How?
So I spent a few weekends Googling, and the answer was way more complicated than I expected. This post is me documenting that rabbit hole.
Why don't we just drink it straight from the cow?
People drank raw milk for thousands of years. Why can't we just.. do that?
Short answer: raw milk can carry salmonella, E. coli, and listeria, among other things. Before pasteurisation was widespread, diseases spread through raw milk were a genuine public health crisis. So yeah, we process it. But the processing is where things get interesting.
The journey from cow to carton
Once milk comes out of the cow, it's cooled immediately to slow bacteria, tested for pathogens, then clarified -- basically filtered to get rid of dirt and debris. Clarified milk is technically the first product -- clean, raw milk ready for processing. Standard stuff so far.
Dairy Production Process
Tap any step for details
Hover any step for details
Then comes the first surprise. Milk isn't just one thing -- it's a complex mix of fats, proteins, vitamins, and minerals all suspended in water. The next step, separation, spins the milk in a centrifuge and splits it into two streams: skim milk and cream -- the first of many divergences in the dairy production process.
From there, standardisation adds cream back into the skim milk to hit a target fat percentage. 3-4% fat? Whole milk. 18-40%? Light cream. Low fat? Just less cream added back -- that's the light blue cap in NZ and Australia.
Dairy Production Process
Tap any step for details
↳ continues from Clarified Milk
├─ Skim Milk path
Produces
├─ Cream path
Hover any step for details
Now we need to make it safe for the trip to your fridge. Pasteurisation -- named after Louis Pasteur -- heats the milk enough to kill harmful bacteria, then cools it back down. The standard method is HTST. There's also UHT -- or long life milk as most people call it -- which can sit on a shelf for months without refrigeration, which is why in much of Europe, South America, and Asia, milk comes in shelf-stable cartons rather than refrigerated bottles.
Then homogenisation forces the milk through a narrow valve gap under extreme pressure, breaking the fat globules into tiny, evenly dispersed particles. Without this step, the cream would float to the top and separate in the bottle.
Package it, ship it, and that's your milk. I thought I was done. But then I looked at the rest of the dairy aisle.
Ok but what about cheese? And butter? And yoghurt? And...
This is where one liquid becomes dozens of products. Remember those two streams from separation -- skim milk and cream? Each one branches into its own tree, and it's.. a lot.
The cream tree is the simpler one. Pasteurise the cream, cool it, then churn it. Churning ruptures the fat globule membranes so the fat clumps together and separates from the liquid. The temperature matters (typically 10-18 degrees C depending on season and cream composition) -- too warm and you get greasy butter with poor texture.
Want buttermilk? Drain the liquid after churning -- that's traditional buttermilk. Want butter? Keep working the solid fat, add some salt, shape it. Want ghee? Heat that butter to remove all remaining moisture and milk solids -- pure clarified butterfat, massive in Indian cooking.
Back on the milk side, things fork again after pasteurisation:
1. Through evaporation; remove the water and you get condensed milk. Add sugar and you get sweetened condensed milk. Keep drying it further with spray drying and you get milk powder -- the stuff you can reconstitute back into liquid milk with just water.
2. Through cultures; add bacterial cultures to pasteurised milk, incubate it, let it ferment. That's yoghurt. Same basic principle gives you kefir (different cultures, tangier, drinkable) and sour cream (cultured cream instead of milk).
3. Through coagulation; this is the cheese path, and it's the most complex branch of all. Coagulation is the process of turning liquid milk into a semi-solid mass -- essentially forcing the proteins to clump together and trap the fat, forming a gel-like structure that can be cut and drained.
The cheese rabbit hole
Cheese starts with milk -- either raw or pasteurised, depending on the variety and local regulations. You add bacterial cultures to develop flavour, then add rennet (an enzyme) or acid to coagulate the milk. This separates it into curds (the solid bits -- mostly casein protein and fat) and whey (the liquid).
From here, the amount of heating, stirring, draining, salting, pressing, and ageing determines what kind of cheese you end up with:
- Soft unripened (cottage cheese, ricotta): minimal processing, barely aged, basically just fresh curds
- Soft ripened (brie, camembert): some draining, aged with surface moulds
- Semi-hard (cheddar, gouda): more heat, more pressing, aged months
- Very hard (parmigiano-reggiano, pecorino): heavy pressing, aged years
There are over 2,000 named cheese varieties worldwide -- some counts go as high as 4,000 depending on how you classify regional variants. All from the same white liquid, just processed differently. Same starting point, wildly different results.
And the whey -- the liquid leftover from cheesemaking? For most of history, smaller producers found uses for it. Ricotta is literally "recooked" whey. But when industrial cheesemaking scaled up in the 20th century, factories were generating far more whey than anyone could use, and a lot of it ended up in rivers (NO WHEY!! pun intended).
Then the sports nutrition industry happened. Today, whey protein is filtered and processed into the stuff in your protein shakes -- a market worth roughly US$10 billion and growing fast. A derivative called lactoferrin now sells for US$200-500 per kilogram -- it's a glycoprotein with antimicrobial properties and there's very little of it per litre of whey, so extracting it is expensive. From river pollution to premium ingredient. Quite the rebrand.
Here's the full picture -- every path from cow to end product.
Dairy Production Process
Tap any step for details
↳ continues from Clarified Milk
├─ Skim Milk path
Produces
├─ Cream path
↳ continues from Cream (from Separation)
├─ Buttermilk
├─ Butter path
↳ continues from Fluid Milks
├─ Drink it
├─ Dry it
├─ Culture it
↳ continues from Fluid Milks (to cheese vat)
├─ Whey (liquid)
├─ Curds (solid)
Cheese types (by aging)
I do this for the love of writing — each subscriber costs me money. But please subscribe anyway and spread the word.
Why is milk so versatile though?
Other ingredients have impressive product trees too. Soybeans give you tofu, tempeh, miso, soy sauce, soy milk, soy oil, lecithin, biodiesel. Corn gives you starch, syrup, ethanol, tortillas, bourbon. Both are versatile. But milk does something different.
Think of it like a skill tree in an RPG. Soy and corn are like ingredients where you pick one processing path and follow it to an end product. Milk is the one where each unlock opens three more unlocks, because you can pull it apart in multiple independent ways. Here's why.
Milk is three things at once:
- An emulsion: fat globules suspended in water
- A colloid: protein clusters floating around in suspension
- A solution: sugars and minerals dissolved in water
Most foods are one of these. Milk is all three simultaneously. And each one responds to a different separation method:
- Density: centrifuge it and the lighter fat separates from the heavier liquid (cream)
- pH: add acid and the proteins clump together (cheese curds, yoghurt)
- Enzyme: add rennet and it triggers coagulation differently than acid does (different cheeses)
- Evaporation: remove water and you concentrate everything that's left (condensed milk, powders)
Four independent methods, each producing intermediates that branch further. Soy and corn can be processed in many ways, but they don't separate into independent streams like this. That's what makes milk's product tree uniquely deep.
The numbers are ridiculous
The world produces nearly 1 billion tonnes of milk per year. From around 270 million dairy cows.
And here's where I get to rep the homeland. New Zealand -- population 5 million, roughly 10 million dairy cows -- is the world's largest dairy exporter, shipping roughly 95% of its milk overseas. Fonterra alone handles about 30% of the world's dairy exports. The entire country basically runs on cows. As a Kiwi, I find it genuinely hilarious that our biggest flex on the global stage is milk.
The conversion ratios are what got me though. 1 kg of cheese takes about 10 litres of milk (parmigiano-reggiano takes 16). 1 kg of butter takes about 21 litres. 1 kg of ghee takes about 30. That wheel of parmigiano at the deli? Around 36 kg, roughly 550 litres of milk, then aged 12 to 36 months.
Speaking of parmigiano -- Italian banks accept the wheels as collateral for loans. Credito Emiliano has been doing this since 1953. They hold around 440,000 wheels in temperature-controlled vaults. The cheese ages, increases in value, and the bank clips interest. Your parmesan is literally bankable.
The global dairy industry is worth roughly US$800-900 billion -- the second or third largest food industry on earth.
Wait, it's also in my buttons?
I assumed milk was just a food thing. Nope. Casein -- the protein that makes up about 80% of milk's protein content -- has been used industrially for over a century:
- Casein paint: used since antiquity, exceptionally durable -- the dried film becomes water-resistant over time. Still produced today.
- Casein glue: the standard wood adhesive for decades. The de Havilland Mosquito, WWII's "Wooden Wonder" fighter-bomber, was assembled with casein glue in its early production run. Milk protein holding together a combat aircraft.
- Galalith: literally "milk stone" in Greek. An early plastic made from casein, developed in the 1890s. Used for buttons, buckles, fountain pens, and jewellery through the mid-20th century. Some vintage "Bakelite" jewellery? Actually Galalith. Actually milk.
- Lactose filler: one of the most common filler substances in pharmaceutical tablets. Your last headache pill probably contained milk.
Cheese is older than lactose tolerance
Humans first started processing milk roughly 8,000-10,000 years ago in the Fertile Crescent. Cheese residues have been found in 7,000-year-old pottery. That's older than the wheel. Older than writing.
Here's the thing -- roughly 65% of the world's adults can't properly digest lactose after infancy. Being able to drink milk as an adult -- lactase persistence -- is the genetic adaptation, not the default. Which means early humans were almost certainly making cheese before they could comfortably drink milk. When you age cheese, bacterial cultures convert the lactose into lactic acid -- the longer the ageing, the less lactose remains. Hard aged cheeses like cheddar or parmigiano have virtually none.
We didn't wait for our biology to catch up. We just.. engineered around it. Thousands of years before anyone knew what an enzyme was.
I went into this thinking dairy was simple. Milk the cow, filter it, put it in a bottle, done. Turns out from that one output you can get fluid milk, cream, butter, buttermilk, ghee, yoghurt, kefir, sour cream, dozens of cheeses, condensed milk, milk powder, whey protein -- and apparently also paint, glue, plastic, and pharmaceuticals.
50+ distinct commercial products. One animal. One liquid. I don't know which freak first looked at a cow and thought "I wonder what happens if I squeeze that and then leave the results in a cave for six months," but I'm glad they did.
PS: If someone tells you they prefer raw milk because it's "more natural" or "less processed" -- send them this article. Specifically the bit about salmonella, E. coli, and listeria.
Disclaimer: Thoughts are my own and do not represent any other parties.
Newsletter
I do this for the love of writing.
Each subscriber costs me money, but please do it anyway and spread the word. Monthly at most.
You might also like
Where did the monuments go?
The Empire State Building took 410 days and came in under budget. Construction is now the only major industry that's gotten worse at its job over 50 years. What happened?
Bird brains
A kea parrot in New Zealand learned to drag traffic cones onto a highway so cars would stop and humans would feed it. That sent me down a rabbit hole on how we actually measure bird intelligence.
The Codification Treadmill
The person who replaces you probably won't be AI. It'll be someone from the next department over who learned to use it.