Pre-Columbian technique adapted and documented by Diana Kennedy, Rick Bayless, and the Mexican culinary tradition.
After toasting, dried chiles must be rehydrated before blending into sauces, moles, and adobos. The soaking technique directly affects the flavour of the resulting sauce: over-soaking produces a bitter, leached sauce; under-soaking produces a grainy, under-integrated purée. Technique: place toasted chiles in a bowl or saucepan and cover with just-boiled water. The ratio matters — use only enough water to barely cover the chiles, as excess water dilutes the soaking liquid (chile water) which often has valuable flavour. Soak for 20–30 minutes until the chiles are completely pliable and the flesh has softened. Drain, reserving the soaking liquid. Blend the chiles with a small amount of the reserved soaking liquid (not the entire quantity — taste the soaking liquid first; if very bitter, use fresh water or chicken stock instead). Blend to a completely smooth purée, at least 2–3 minutes in a high-speed blender. Pass through a medium-mesh sieve to remove skin fragments and seeds.
The soaking liquid carries dissolved sugars, carotenoids, and capsaicin from the chile. Its bitterness level varies significantly by variety — guajillo soaking liquid is reliably usable; pasilla soaking liquid should be tasted before use.
Just-boiled water, not simmering water — the temperature difference matters: water at a full boil loses temperature too fast; a covered soak in just-boiled water maintains warmth throughout Reserve the soaking liquid — it contains dissolved flavour compounds; use cautiously as it can be bitter, especially from guajillo and chile de árbol Blend for at least 2 minutes — a properly blended chile sauce is silky; insufficient blending produces a gritty texture Strain through a sieve — the skin fragments that escape even a high-speed blender will ruin the sauces texture in fine applications
For moles requiring multiple chile varieties, soak each variety separately — different chiles rehydrate at different rates For salsa borracha (drunken salsa), replace the soaking water with beer or pulque — this technique is literally in the name A small amount of oil added to the blender with soaked chiles acts as an emulsifier and produces a silkier, more integrated sauce
Soaking in cold water — adequate rehydration takes significantly longer and produces inferior flavour extraction Using all the soaking liquid in the blend without tasting it first — bitter soaking liquid is one of the most common causes of an overly harsh sauce Not straining — skin fragments create a rough texture and visual speckling
Rick Bayless, Authentic Mexican; Diana Kennedy, The Art of Mexican Cooking