Infusing A Liquid Depends On What Dissolves In What

Steeping garlic in oil and simmering it in stock give two different results from the same clove. The liquid determines which compounds leave the ingredient and which stay behind.

Two families of flavour compounds

Some flavour molecules dissolve readily in water, including many acids, sugars and the compounds behind savoury depth in dried mushrooms and seaweed.

Others dissolve only in fat, including most of what gives chilli its heat, turmeric its colour and many of the aromatic compounds in spices and herbs.

An infusion made in the wrong medium therefore extracts a partial version of the ingredient, which is why the same spice can taste thin in a broth and vivid in oil.

Blooming spices is an oil extraction

Frying ground spices briefly in fat at the start of a dish dissolves their fat-soluble compounds into the oil, which then carries them through everything else.

Because the oil coats the other ingredients, the flavour is distributed rather than concentrated in undissolved specks of powder.

The window is short, since the same heat that extracts also destroys, and spices in fat pass from fragrant to burnt in under a minute.

Temperature sets the speed and the ceiling

Higher temperatures extract faster because molecules move more and solubility generally increases, which is why hot infusions are quick.

But heat also drives off volatile aromatics and can extract bitter compounds that a cool infusion leaves alone, which is why delicate leaves are steeped briefly.

Cold infusion is slow and selective, taking hours to produce a result that is often cleaner and less bitter than the hot equivalent of the same ingredients.

Surface area and time do the rest

A whole spice infuses slowly because only its outer surface is in contact with the liquid, while a ground one exposes everything at once.

That makes whole spices right for long cooking, where they release gradually, and ground ones right for short cooking, where there is no time to wait.

Bruising, cracking or slicing sits between the two and is often the useful compromise, giving faster release while still allowing the pieces to be removed.

Alcohol and acid extract differently again

Alcohol dissolves both water-soluble and fat-soluble compounds to a degree, which is why it extracts more completely than either water or oil alone.

Acidic liquids extract colour and some compounds particularly well, and also change how ingredients behave, softening some and firming others.

Infusions in oil are also the ones needing most care in storage, since a low-acid, oxygen-poor mixture containing fresh ingredients is not a safe thing to keep at room temperature.