A raw agave heart tastes of almost nothing sweet. Its sugars are locked away as long chains called inulins, and no yeast can ferment them as they are. So before there is any tequila, there has to be heat. How a house chooses to cook its agave is one of the quietest decisions in the whole process, and one of the most telling.
The oldest way is the horno, a masonry oven of stone or brick. The halved piñas are stacked inside, sealed in, and steamed slowly, often over a day or more, then left to rest as the oven cools. The fibres soften and darken, and the sugars turn simple and caramel-edged. Spirits from slow-oven agave tend to carry a cooked, honeyed depth, with notes of baked sweet potato, a little smoke-free earth and a rounded body.
The autoclave is the horno's modern relation: a steel pressure vessel that cooks the same piñas in a fraction of the time. Done with patience, it gives a clean, bright agave character, a little greener and more peppery than the oven's warmth. Many respected producers use autoclaves, and the method alone says nothing about quality. What matters is how gently the cook is run.
The diffuser is a different idea altogether. Instead of cooking whole piñas, it shreds raw agave and rinses the sugars out with hot water, sometimes helped by acid, before any slow cooking happens. It's efficient and consistent at scale. Its critics, and there are many among agave purists, find the result flatter, with less of the cooked-agave soul that defines the spirit.
None of this sits on most labels, which is why it's worth asking. When a bottle speaks of brick ovens or slow cooking, it's telling you something real about the hours behind it. A maison should know where its agave was cooked, and how long it was given.