A Quick Starch Primer

• Starches consist of thousands of smaller sugar molecules, bound tightly together into chains. There are two basic types, and both are found in your flour. Amylose forms into long strands, while amylopectin molecules are shorter and bushier. Amylose is the starch that dissolves into liquids and thickens your gravy, while amylopectin is the starch that absorbs water and makes your pasta tender. In baked pastries, both contribute to the final texture of the crumb.

Hydration

• The first step in transforming the flour's starches from dusty grit to tender pastry occurs when it's moistened. The granules of starch are naturally dry and porous, so they absorb enough water to increase their weight by about 30 percent. This takes several minutes, which is why a cake or muffin batter tends to thicken and become stiffer after resting for several minutes. Bread dough such as brioche, and unleavened dough such as puff pastry, gain a smoother and more elastic texture as the moisture travels between starch granules like melted wax flowing through a candle's wick. The moisture also hydrates the flour's proteins, creating gluten chains that give structure to the finished product.

Gelation

• Hydration is just a preliminary to the main change in the starches' structure, which happens when you slide your pastries into the oven. As the starches reach temperatures between 120 and 140 degrees Fahrenheit, the molecular bonds holding the starch granules together abruptly weaken. The molecules swell up, increasing their ability to absorb moisture, and this in turn weakens their molecular bonds further. The long strands of amylose are freed to thicken liquids in the dough or batter, while the amylopectin absorbs moisture like a sponge. The combined effect of the two starches is to immobilize most of the moisture, a process called gelation.

Cooling

• Gelled starches are much larger than the original granules, and as they cool they slowly become firm. Like the proteins from flour and eggs, they contribute to the physical structure of your pastry's crumb and help it hold its shape. It's important to let the starches cool to below their gelation point before slicing any moist pastry or yeast dough. If they're still in their softened gel form, they'll become dense and doughy even if they're properly baked. It's the same as slicing into fresh-baked bread before it cools: It has its own appeal, but the texture will never be right.

Browning

• Starches serve one other purpose: They to contribute to the flavor of your pastry. Starches are composed largely of sugars, and those sugars caramelize in the oven's intense heat. The caramelization, and a secondary browning process called Maillard reactions, breaks up the flavor molecules in the starches and forces them to recombine into smaller fragments. These processes create a range of complex sweet, nutty and toasty flavors, contributing to both the visual and the culinary appeal of your pastries.