A nut paste is ground until the oil becomes the liquid

Nuts are a solid that contains its own liquid

Almonds, hazelnuts and pistachios are roughly half fat by weight, but that fat sits locked inside cell structures rather than sloshing about freely. Grinding is the process of rupturing those cells so the oil is released, and the point at which a nut flour turns into a paste is the point at which enough oil has escaped to form a continuous phase. Beyond that, the ground solids are suspended in their own fat rather than sitting as dry powder.

This is why nut pastes cannot be made in a hurry. Early in grinding the material heats, clumps and looks as if it will never come together; keeping going takes it through a gluey stage and then, quite suddenly, to something that flows. Machines built for the job use stone rollers precisely because the process needs sustained shear rather than impact, and domestic food processors manage it only with patience and periodic rests.

Praline is caramel and nuts ground into one material

The classical praline paste begins with nuts cooked into a caramel, cooled to a brittle sheet, then broken and ground. Two solids are being reduced simultaneously, and they behave differently: the caramel is a sugar glass that shatters into hard fragments, while the nuts release oil. The oil ends up coating the sugar particles, which is what turns what should be an unworkable grit into a smooth, pourable paste with no added fat at all.

The terminology is genuinely inconsistent across countries, which trips people up constantly. In much of Europe praline denotes this caramelised nut paste or the filled chocolates made with it; in parts of the United States the word names a soft sugar and pecan confection that is a different thing entirely. Neither usage is wrong, they simply developed separately, and a recipe is worth reading through before assuming which tradition it belongs to.

Gianduja is what happens when chocolate meets that paste

Combining nut paste with chocolate produces a material noticeably softer than chocolate alone, and the reason is the oil. Hazelnut oil is liquid at room temperature, unlike cocoa butter, so introducing it dilutes the crystalline fat structure and lowers the melting behaviour of the mixture. Gianduja sets, but softly, and it cannot achieve the snap of a plain bar because a substantial fraction of its fat never crystallises in the first place.

That softness is the appeal rather than a defect, and it also explains the historical origin: nut paste was extended into chocolate at a time when cocoa was scarce and expensive in northern Italy, and the resulting material proved popular enough to outlive the shortage. The modern nut spreads on supermarket shelves are distant descendants of the same idea, generally with added vegetable fat and considerably more sugar than the confectioner’s version carries.

Marzipan solves the same problem with sugar instead of heat

Marzipan is ground almonds and sugar, sometimes bound with a little syrup or egg white, and it holds together for a different reason. Here the sugar is present in enough quantity to form a dense continuous phase of its own, with almond oil and solids distributed through it. The result is firm, mouldable and stable at room temperature, which is why it works as a modelling material in a way that a pure nut paste never could.

The ratio decides the character completely. A high almond proportion gives a rich, oily paste that is prized for eating but difficult to roll thin; a high sugar proportion gives a firmer paste that handles well and tastes mostly of sugar. Persipan, made from apricot or peach kernels rather than almonds, exists chiefly because those kernels were cheaper, and it is labelled separately for good reason rather than sold as the same product.

The failures are all about oil and heat

Nut pastes separate. Left standing, the oil rises and pools on top, exactly as it does in a jar of unstabilised peanut butter, and the answer is to stir it back rather than to pour it off. Anything made with a nut paste is also more prone to bloom, because the liquid oil migrates slowly through a chocolate shell and disrupts the crystal structure from within. Filled sweets containing praline have a shorter honest shelf life than plain ones for this reason.

Heat is the other constraint. Grinding generates it, and nut oils are relatively unsaturated, so they oxidise and turn rancid faster than cocoa butter does. Roasting the nuts before grinding improves flavour substantially and is nearly universal practice, but it also starts the clock. Nut pastes are best kept cool, sealed and used within months rather than years, which is a genuine limitation and not a manufacturer being cautious.