Milk and orange juice are classic American breakfast staples, with fried eggs and bacon, of course.
Some believe, however, that flushing orange juice with milk is a recipe for throwing up. The idea behind this myth is that when you mix orange juice with milk, it curdles in your stomach, making you nauseous.
Ali Rezaie, a gastroenterologist at Cedars-Sinai Medical Center in Los Angeles, graciously refutes this belief.
Why does milk curdle in orange juice?
Milk and orange juice are on very different parts of the pH scale, which measures how acidic or alkaline (or basic) a substance is. Chemically, an acid is a substance that produces hydrogen ions when dissolved in water. An alkali produces hydroxide ions when dissolved in water. The pH scale goes from 0 to 14, with 7 being neutral, like water. Substances below 7 are acids and those above 7 are alkalis.
Orange juice, according to Rezaie, has a pH of 4. Cow’s milk hits just under 7, at 6.8 or 6.9, making it neutral for the most part.
Milk is made up of casein proteins, lactose, lipids and water. Casein proteins are quite fragile, so changes in milk acidity will cause them to clump together into curds. When milk is at its ideal pH level, the proteins are fully dissolved. The acidity of orange juice breaks down proteins into discrete coarse clumps.
What happens when I drink orange juice and then milk?
Rest assured, according to Rezaie, you’ll digest them both with no problem.
Stomach acid gives orange juice its money’s worth with a pH level between 1.5 and 3. This may not seem like a big difference, but the pH scale is logarithmic, which means changes are exponential; an acid at 3 is ten times more acidic than an acid at 4, and an acid at 2 is 100 times more acidic than one at 4. Thus, stomach acid at 1.5 is 250 times more acidic than juice orange.
“There’s a ton of acid in your stomach all the time,” says Rezaie Reverse. In a day, the stomach produces about half a gallon of acid.
Everything you consume is plunged into a vat of stomach acid which goes to work breaking down everything, including the protein curds. “It doesn’t matter whether you added orange juice or not right away,” says Rezaie. “It’s down.” Stomach acid is much stronger than orange juice, so your stomach can handle both together.
For those who get sick from dairy, the problem is usually lactose, a carbohydrate, which makes them lactose intolerant. This means they don’t have the enzyme lactase to break it down properly, which can cause a gnarly stomach upset.
What if I drink milk mixed with orange juice?
Probably not much. Many smoothies mix milk and orange juice or another acidic fruit, like pineapple. Many of us enjoyed the orange and vanilla ice cream bars with no problem. The worst that can happen is curds getting stuck in your teeth.
PLEASE CHECK is a Reverse series that uses biology, chemistry and physics to debunk the biggest food myths and hypotheses.
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