TECHNIQUE GUIDE

Cooking technique guide

Check the core principles of cooking techniques and how to handle ingredients step by step.

COOKING TECHNIQUE

Zolgi

Reduction is a cooking method that boils down a cooking liquid or seasoning to evaporate moisture and concentrate flavors and thickness to the desired state. It is used to infuse the ingredients with seasoning while turning the liquid into a glossy sauce or rich broth. Initially, cook the ingredients in relatively abundant liquid, and as you go back, monitor the rate of reduction. Since moisture decreases, saltiness and sweetness intensify, so adjust by anticipating the seasoning after reduction rather than the final taste. Reduction is especially suited for ingredients that can absorb flavors and maintain shape, such as fish, meat, and root vegetables. Conversely, leafy vegetables or very delicate seafood can become soggy or tough if reduced for too long, so it is better to cook briefly or add them at the end.

Core principles

As the surface liquid evaporates, the seasoning components stay behind and the ingredient surface develops a richer flavor and gloss. If the liquid is thin and the ingredients are not fully cooked, open the lid to increase evaporation, and keep in mind that a wider surface area reduces the liquid more quickly.
If you start with a high heat to reduce quickly, sugars or proteins on the surface may scorch first. Keep the boil steady when there is plenty of liquid, and lower the heat to finish thickening as the amount decreases and the ingredients begin to emerge.
The size and firmness of the ingredients determine the rate of cooking. Hard ingredients like daikon or potato should be cut into similar sizes and submerged in broth, while already cooked or soft ingredients should be added later to preserve shape.
As the reduction cools, the sauce may feel somewhat thicker. If it seems too viscous on the heat, don't finish immediately—scoop a spoonful to cool briefly and observe the flow, and add water or stock if needed.

Well-matching ingredients

Suitable for reduction where strong-seasoned sauces like soy sauce, gochujang, or doenjang are used with water or stock. Because the seasoning reduces and the saltiness and sweetness intensify, it is better to reduce the amount and concentration of seasoning for delicate ingredients.
Fish such as mackerel, chicken or pork, tofu, mushrooms, and vegetables like radish, potato, and lotus root absorb flavors well during reduction. However, tofu and delicate fish can break if flipped many times, so it's advantageous to cook by ladling the broth over them in a wide pan.
Fatty cuts of meat or fish can layer in the developed flavors, but very fatty parts may cause the sauce to separate and feel heavy. In that case, skim off the rising fat early or consider adding a small amount of acidic ingredient.
Vegetables with high moisture like zucchini, leafy greens, or shrimp are not ideal as the main ingredient for long reductions. Add them toward the end or cut down on their cooking time to minimize moisture loss and texture damage.

Heat and time management

The reduction time is determined by both the time needed for the ingredients to become tender and the time for the sauce to reduce. If the sauce reduces first while the ingredients are still firm, add hot water or stock to compensate, and if the ingredients are done but the sauce is plentiful, uncover and raise the heat one notch to finish.
Start at medium heat to ensure even boiling, then once boiling begins, keep a gentle simmer so ingredients do not clash excessively.
Lids help retain moisture and heat in the early phase of cooking, but in the later phase when concentration is needed, the lid should be removed. If the sauce still doesn't reduce well after removing the lid, transfer to a wider pan for safety and better evaporation.
In the final stage, the sauce should coat the bottom of the pan thinly; scoop with a spoon and observe the flow so it does not pour out like water instantly. Sweetened sauces also thicken quickly in the last few minutes, so stay attentive and adjust as needed.

Success points

Using a wide pan so the liquid can spread in a single layer helps the sauce contact evenly and makes evaporation easier. If the pot is too deep and ingredients overlap, gently shake the pan or baste the broth over them.
Begin with seasoning slightly milder than the final desired taste to be safe. If during reduction it tastes too salty, add water or unsalted stock and then adjust the final seasoning.
When turning ingredients, avoid frequent stirring with chopsticks; tilt the pan by holding the handle and baste the liquid. Especially with fish and tofu, flip carefully once, or you can cook by basting the top with broth without flipping.
After completion, turn off the heat and let rest briefly so the seasoning adheres more evenly to the surface. However, sauces thickened with starch may set too firmly if left too long, so if needed, add a small amount of water right before serving to loosen.

Common mistakes

It is common for the sauce to become overly salty and sweet after tasting early because there is still a lot of sauce left. If so, adjust by adding water or unsalted stock and reduce again, next time starting with less seasoning.
Boiling on high heat from start to finish can cause the bottom to scorch and the ingredients to break. If you notice a sticky smell at the bottom or the sauce bubbling rapidly at the edges, reduce heat immediately and, if needed, transfer to another pan and avoid stirring the burnt parts.
If you reduce too little and extend time, the ingredients may break apart or the fish may dry out. If the ingredients are already cooked, uncover and reduce quickly in a wide pan to shorten cooking time.
Conversely, trying to cook hard ingredients when there is not enough sauce can cause the seasoning to scorch and the interior to be undercooked. If a piece like daikon or potato does not slide easily with chopsticks, add hot liquid so they are halfway submerged, and finish once they become tender.
Judging final thickness only on the stove can cause the sauce to become too thick once cooled. If the desired state is slightly runny, turn off the heat and check the viscosity of the cooled liquid, then reduce again only if needed.