Xiaolongbao Craft: Aspic, Pleats, and Why Thickness Is a Variable

The engineering problem

Xiaolongbao is an engineering challenge wearing a dumpling’s face. The goal is to have hot liquid broth inside a thin flour wrapper after steaming — but you can’t fill a raw dough wrapper with liquid and fold it closed. The liquid would break the seal. So the broth has to enter the wrapper as a solid and become liquid during cooking.

The solution is aspic: stock reduced and gelled with collagen until it sets solid at refrigerator temperature. You dice it, mix it into raw pork mince, fill the dumpling, and the cold solid holds through assembly. The steamer’s heat — 100°C sustained for 8 minutes — melts the aspic back into broth while simultaneously cooking the pork and setting the wrapper.

This is not a recipe trick. It is applied food chemistry, and understanding it changes how you approach every step of making xiaolongbao.

Making aspic that actually gels

The aspic is where most home attempts fail. Commercial operations use a standardized pork skin and trotter reduction; home cooks often try to shortcut with powdered gelatin. The results are different in texture and flavour.

A proper aspic for xiaolongbao starts with pork trotters or skin (ideally both), covered in cold water, brought to a boil, drained (to remove scum and excess fat), then simmered for 3–4 hours in fresh water with minimal seasoning — a few slices of ginger, some Shaoxing wine, a small amount of soy. The liquid should reduce to roughly a third of its starting volume. Strain, cool, and refrigerate overnight. The result should be firm enough to dice into 5mm cubes and hold its shape at room temperature for at least 15 minutes.

If you get aspic that sets soft (wobbles but doesn’t hold a dice), your reduction wasn’t far enough. If you get aspic that weeps liquid even cold, your collagen ratio was too low — use more trotters.

Powdered gelatin works as a substitute but produces a different mouthfeel: the broth will be thinner and less unctuous. If you use it, bloom 12g of gelatin per 500ml of good quality stock, heat gently until dissolved, pour into a shallow tray, and refrigerate overnight.

Fuchsia Dunlop’s Every Grain of Rice (2012) includes the clearest English-language ratio guidance for aspic reductions in Shanghainese cooking; it’s the reference to trust when your first batch doesn’t hold.

Wrapper hydration and thickness

The wrapper is the other variable cooks underestimate. Standard jiaozi wrappers from a Chinese supermarket are too thick — they’ll hold the filling but produce a chewy result. The wrapper for XLB needs to be thin enough to admit the broth on the bite and translucent enough to show the filling through.

The dough is hot-water (scalded) dough: approximately 200g plain flour to 90–100ml just-boiled water, mixed quickly and kneaded until smooth, rested 30 minutes covered. Hot water partially cooks the starch, producing a softer, more pliable dough that stretches without tearing.

Thickness is not uniform. A properly rolled XLB wrapper is thinner at the edges (where the pleats will be gathered) and slightly thicker at the centre base (where the weight of the filling will stress the seal). Most rolling pins make this difficult; a tapered Chinese rolling pin (available in most Chinese kitchenware shops) lets you thin the edges while leaving the centre intact.

Target thickness: 1mm at the edge, 1.5–2mm at the centre. Too thin at the centre and the base tears on lift; too thick at the edge and your pleats will be clumsy and bulky.

The best source for the tapered rolling pins and other XLB-specific tools is asian-food.store → rolling pins — the 35cm tapered model is what professional XLB makers use.

The 18-pleat standard and what it actually measures

The 18-pleat count associated with Din Tai Fung is not arbitrary tradition. It’s a functional measure of fold density.

Each pleat is a fold of wrapper brought up around the filling and pinched into the spiral gather at the top. More pleats = smaller, tighter folds = denser seal = lower probability of burst during steaming or on the lift from the basket.

18 pleats requires a wrapper with a diameter of roughly 8–9cm and a fold width of about 3mm. Home cooks producing 12–14 pleats on a 9cm wrapper are leaving wider folds that have more surface area to fail.

The technique: hold the filled wrapper in your non-dominant hand, cupped to shape it. With your dominant hand, pinch a small section of edge between thumb and forefinger, fold it toward the centre, and pleat it against the previous fold as you work around the circumference. The top gathers naturally into a twist. The speed comes from synchronizing the hand holding the dumpling (which rotates to bring fresh edge to the pleat) with the pleat hand.

Your hands’ heat is your enemy. Warm palms start melting the aspic in the filling, which makes the dumpling sag and is harder to seal. Work fast, or work in a cool room.

Bamboo, not metal, and why this matters

Metal steamers collect condensation on their lids and drip it back onto the dumplings. That condensate water softens the wrapper and causes breaks — structurally and aesthetically. Bamboo steamers absorb the steam and wick moisture away from the lid.

This is not preference. Dim sum kitchens use bamboo because it produces a consistent product. For equipment guidance, see our detailed piece on xiaolongbao origin and the regional tradition for context on why Shanghainese cooking standards evolved as they did.

Steam time: 8 minutes at a rolling boil. Check by gently pressing the side — taut and springy means done; slack means 90 more seconds.

The eating dimension

Craft without consumption context is incomplete. The ritual of eating XLB correctly — the bite, the sip, the dip — is covered in detail in xiaolongbao eating ritual and etiquette. But the short version: the broth you spent three hours engineering into a solid should be the first thing you taste, not something you accidentally spray on your neighbour.