Pickles & ferment bases
Aaruul
Ааруул · A traditional Mongolian preserved-dairy preparation in which naturally soured milk curds are strained, pressed into a slab, cut into pieces, and sun-dried to yield a hard, chewy, tangy, shelf-stable curd. Functions as both a standalone travel snack and a reusable dairy building-block for soups, stews, and teas in nomadic cuisine.
The formula
Fresh pressed curds : dried aaruul ≈ 4:1 by weight (variable with milk type and drying)
No fixed ratio; yield depends on curd moisture, milk source, ambient humidity, and target firmness.
Identity
- Traditional Mongolian preserved dairy
- Sun-dried lactic-fermented curd
- Nomadic travel provision (paired with borts)
- Member of tsagaan idee ('white foods') tradition
- Foundational dairy base for soups, stews, and tea
- Shelf-stable curd without added salt or vinegar
Ingredients
| Base | Milk curds (cow, yak, camel, sheep, or goat) | Whole milk is soured until it separates; the solid curds form the body of the preparation. |
| Culture | Tarag or naturally occurring lactic ferment | Inoculum of lactic acid bacteria — provided by traditional tarag starter, by raw-milk microbes, or in modern shortcuts by plain yogurt. |
| Seasoning | Salt (optional) | Used only in some modern simplified recipes (e.g., yogurt-based versions); traditional sun-dried aaruul is typically unsalted. |
Method
- 1Sour fresh milk (cow, yak, camel, sheep, or goat) until it curdles naturally — traditionally by adding a portion of tarag or by leaving raw milk to ferment.Lactic acid fermentation drops the pH, causing casein to coagulate and whey to separate; this is the foundation of the curd and imparts the characteristic tang.
- 2Lift the curds with a fine cloth and let the whey drip off; gather the solid mass.Removing whey concentrates the curd and shortens drying time, while the fine cloth retains the soft curds intact.
- 3Press the drained curd between two wooden boards weighted with stones to form a compact cake a few centimetres thick.Pressure expels residual whey and fuses the curds into a uniform, shapeable slab that dries evenly and resists crumbling.
- 4Cut the pressed cake into pieces roughly 10 cm long.Standardised sizing gives consistent drying rates and produces the portable pieces that fit in a saddlebag or pocket.
- 5Arrange the pieces on a wooden board and sun-dry on the yurt roof (or another open, breezy surface), shielded with a fine white cloth to deter birds.Strong sunlight, dry air, and gentle heat drive off remaining moisture; the cloth cover keeps flies and birds off while still allowing airflow.
- 6Continue drying until the pieces are firm, hard, and cheese-like — typically several days up to about two weeks depending on weather.Sufficient water activity loss is what makes aaruul shelf-stable almost indefinitely without refrigeration.
Techniques that matter
Natural lactic fermentation (souring)
Produces both the curdling and the characteristic sweet-sour flavour profile without commercial starters.
Cloth straining of whey
Concentrates the curd and prepares it for pressing.
Weighted-board pressing
Forms a dense, uniform cake that can be cleanly portioned and that dries without collapsing.
Sun-and-air drying
Provides the low-humidity heat needed for shelf stability and the gentle Maillard-like browning that builds depth of flavour.
Variations & derivatives
Yak-milk aaruulMongolian highlands, Altai/Tuva borderlands
Made from rich yak milk; yields a particularly dense curd with a stronger tang.
Camel-milk aaruulTrans-Altai Gobi and southern Mongolia
Subtly different flavour, slightly higher natural sweetness; well-adapted to arid southern regions.
Cow-milk aaruulNorthern and central Mongolia
The most common everyday version; milder and more uniform in taste.
Yogurt-salt shortcutModern urban Mongolian kitchens
Plain unsweetened yogurt + a small amount of salt is strained/dried directly, bypassing the multi-day tarag souring step.
Used in these dishes
Substitutions
- Cow milk → Yak, camel, sheep, or goat milk — All listed milks are authentic; regional availability dictates choice and shifts the flavour profile.
- Traditional tarag inoculum → Plain unsweetened yogurt — Yogurt provides the same lactic acid bacteria and is an acceptable modern shortcut for souring the milk.
- Sun-drying on roof/platform → Oven drying on low heat or dehydrator — Lower temperature or desiccation is needed indoors; finish will be less sun-browned but still shelf-stable.
Troubleshooting
Drying pieces develop surface cracks or crumble
Drying too fast or pieces too thin → Move to a less direct sun position and use slightly thicker cuts (close to 10 cm) to slow moisture loss.
Birds or insects take pieces during drying
Open-air drying on roof without protection → Cover the drying board with a fine white cloth — traditional solution that keeps pests off while preserving airflow.
Pieces become so hard they cannot be bitten
Over-drying in dry, hot conditions → This is normal; suck rather than chew the pieces, or rehydrate briefly in warm water/milk before adding to dishes.
Aaruul tastes flat or only sour, with no sweetness
Insufficient souring time or low-quality milk solids → Extend tarag fermentation for fuller acid development, or use a richer milk (yak/sheep) to recover body and sweetness.