Quark has two very different meanings depending on whether you’re in a kitchen or a physics lab. In the dairy world, quark is a soft, creamy fresh cheese popular across Central Europe, packed with more protein than Greek yogurt. In particle physics, quarks are the fundamental building blocks inside protons and neutrons, the tiniest known components of matter. Both meanings come up frequently in searches, so here’s what you need to know about each.
Quark as a Dairy Product
Quark is a fresh, unaged cheese made from pasteurized milk. It has a smooth, spreadable texture somewhere between yogurt and cream cheese, with a mild, slightly tangy flavor. It’s a staple in German, Austrian, and Scandinavian cooking, used in everything from cheesecakes to savory dips to breakfast bowls.
To make quark, producers add specific bacterial cultures to milk, primarily strains of Lactococcus. These are different from the cultures used in yogurt. A small amount of rennet is also added to help the milk coagulate. After the milk thickens over many hours at a controlled temperature, the whey is drained off through cloth, sometimes for 16 to 22 hours, until you’re left with a thick, creamy curd. The result is softer and wetter than most cheeses but denser than yogurt.
Quark can be made from skim or full-fat milk, which is why you’ll see it sold in a range of fat levels. Low-fat and fat-free versions are especially popular among people looking for high-protein dairy options.
Quark Nutrition Compared to Greek Yogurt
Quark typically delivers 10 to 14 grams of protein per 100 grams, compared to 8 to 10 grams for Greek yogurt. It also tends to have slightly less sugar and a milder flavor. That protein density, combined with its thick texture, has made quark increasingly popular outside of Europe as a higher-protein alternative to yogurt.
Because quark is made with live bacterial cultures, some varieties may contain active probiotics at the time of purchase. However, whether those cultures survive processing depends on the brand and how it’s handled. If live cultures matter to you, check the label for confirmation, just as you would with yogurt.
How to Use Quark in Cooking
In Central European kitchens, quark is incredibly versatile. It’s the base for traditional German cheesecake (Käsekuchen), which has a lighter, less dense texture than American-style cheesecake. It works as a spread on bread with herbs or fruit, gets stirred into pasta sauces for creaminess, and serves as a filling for pastries and dumplings.
If you can’t find quark at your local grocery store, the closest substitute is strained Greek yogurt. Draining Greek yogurt through a clean kitchen towel in the refrigerator for a day or two thickens it to a quark-like consistency. Mascarpone works in some baking applications but is much higher in fat and lacks the tanginess. Buttermilk can also be used as a base to make a homemade version.
Quarks in Particle Physics
In physics, a quark is one of the most fundamental particles in the universe. Quarks combine to form protons and neutrons, which in turn make up every atomic nucleus. They are, as far as scientists can tell, indivisible. You cannot break a quark into anything smaller.
The name comes from physicist Murray Gell-Mann, who in 1964 proposed (along with George Zweig) that the hundreds of subatomic particles known at the time could be explained as combinations of just a few fundamental building blocks. Gell-Mann borrowed the word “quark” from a line in James Joyce’s novel Finnegans Wake: “Three quarks for Muster Mark!”
The Six Flavors of Quarks
There are six types of quarks, whimsically called “flavors”:
- Up and down are the lightest and most common. Every proton contains two up quarks and one down quark. Every neutron has two down quarks and one up. These two flavors account for essentially all ordinary matter.
- Charm and strange are heavier. The strange quark is about 30 times heavier than an up quark, and the charm quark is roughly 400 times heavier.
- Top and bottom are the heaviest. The top quark is the most massive of all, weighing about as much as an entire atom of gold. These heavy quarks existed in abundance right after the Big Bang but today only appear briefly in high-energy particle collisions.
Each quark carries a fractional electric charge, either +2/3 or -1/3 of the charge on a proton. Up, charm, and top quarks carry +2/3. Down, strange, and bottom quarks carry -1/3. This is unusual because most familiar particles have whole-number charges.
Why Quarks Are Never Found Alone
One of the strangest things about quarks is that you can never isolate one. Quarks carry something called “color charge,” which has nothing to do with visible color. It’s a property, like electric charge, that governs how quarks interact with each other. There are three types of color charge, and quarks must always group together in combinations where the color charges cancel out, producing a “color neutral” composite.
This requirement is called confinement. If you try to pull a quark away from its partners, the force between them doesn’t weaken with distance the way gravity or electromagnetism does. Instead, the energy stored in the field between the quarks keeps increasing. Eventually, there’s so much energy in that stretching field that it snaps, and that energy converts into a brand-new pair of quarks. You end up with more quarks rather than a free one. It’s a bit like trying to isolate one end of a magnet by cutting it in half: you just get two smaller magnets.
Quarks are the only fundamental particles that experience all four known forces of nature: gravity, electromagnetism, the strong force (which binds them together inside protons and neutrons), and the weak force (which allows them to change flavor, as happens in radioactive decay). That combination makes them unique in the Standard Model of particle physics.