Cooking & Milling the Agave Heads

 

Once the piņas have been harvested, they are usually split into halves or even quarters, depending on their size. These are carefully stuffed by hand into the ovens for cooking.

 

The top (corta) of the head is cut out before loading  - this is the place where the quiote emerges and producers say it makes the tequila bitter if left intact.

 

Before the late 19th century, piņas were cooked in rock-lined pits in the ground, like agave for mezcal is still cooked today. However, increasing demand for tequila meant increased demand for wood, and Jalisco's forests were soon denuded. Distillers turned to above-ground ovens and coal- or gas-fired heating.

 

In 1864, Manuel Payno published his work Memoria sobre el maguey mexicano y sus diversos productos. In it he described a transitional stage horno as: "similar to the kilns for baking bricks or limestone." He then described the cooking process:

 

When the oven is full, a fire is lit in the lower part, and once it is burning brightly, the opening is blocked with agave leaves and earth, so as to avoid any heat loss. This system is highly economical with respect to fuel, for as soon as the logs catch fire, the workers begin blocking the upper part with agave leaves, and when the heat reaches that part, they promptly shovel earth over the whole thing, so the mezcal remains insulated for as long as it takes to bake through and through.

 

Cooking the agave is a required step for tequila because the heat gently and slowly transforms the agave's natural carbohydrates and starches into fermentable sugars.

 

All cooking ovens today are steam-heated, above-ground ovens that use pressurized steam to cook the agave. Older ovens are stone or brick-lined, newer ovens are stainless steel autoclaves.

 

Farmers who sell piņas by weight may leave on more of the penca, or leaf, while those paid daily wages by the producer are more likely to cut them off closer to the piņa.

 

It takes about 7 kilograms of piņa to produce 1 litre of 100% agave tequila - which means the average piņa can make 2-5 litres. It has also been said that small distillers may simply purchase agave syrup to ferment, without any of the intervening processes, but this author has yet to see this happen. Given the glut of agave at present, this would seem unnecessary.

Some distillers will 'pre-cook' the piņas to rid them of external waxes and solids that may be retained in the leaf (penca) at its base. These can make a bitter or unpleasant juice. These distillers will let this 'bitter honey' collect for a couple of hours in the oven, then drain it off.

 

The steam-injected autoclaves used in modern distilleries also wash away any external materials from the piņas.

 

The traditional stone or brick oven is called a horno - hence the name of Sauza's Hornitos. Traditional distillers (tequilleros) let the piņas soften in the steam ovens or for 50-72 hours at moderate heat. This bakes the agave to process its natural juices at around 140-185 degrees F (60-85C - others may be lower: 135-145F; 57-62C). A few will cook them at higher temperatures: 175-200 F( 80-95C).

 

This slow-bake process softens the fibres and helps keep the agave from caramelizing, which can add darker and bitter flavours to the juice and reduces the agave sugars. Baking in sealed ovens also helps retain more of the natural agave flavours.

 

The moderate heat in the oven breaks apart the long starch molecules into shorter, fermentable sugar molecules. Too high and the sugars caramelize. Too low and the molecules don't break apart.

 

As the agave heads cook, they release moisture and change colour, from white to dark yellow to brown and rusty orange.

 

The juices released from the head collect at the bottom of the oven. Most ovens have a valve system that allows producers to drain away the first couple of hours of liquid - called the bitter honey because it is full of impurities and waxes from the plant - and again at the end of the distillation, when the sweet liquid is added to the fermenting tank.

 

Here's where mezcal and tequila part ways: mezcal piņas are baked slowly in underground pits, rather than steamed. Mezcal agave take on the aromas and flavours imparted by the burning wood and the earth cover. Tequila agave have no such influences.

 

Many large distillers prefer to cook their piņas faster in efficient steam autoclaves and pressure cookers in as little as a single day (12-18 hours). These big pressure cookers can cook the agave at much higher temperatures than the traditional oven.

 

No matter which method is used ,the baking process turns the complex carbohydrates into fermentable sugars and softens the piņa so they can easily release their juice.

 

Fresh from the oven, the piņas taste a bit like a sweet potato or yam, sometimes a little like burnt honey, with a mild tequila aftertaste.

 

In traditional distilleries, the piņas are allowed to cool for another 24-36 hours after steaming, then they are mashed to separate the pulp (bagazo or bagasse) from the juice (although some traditional distillers keep them together during the fermenting).

 

The cooked agave will have 14-17 Brix of sugar.

 

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Crushing the baked agave to extract the juices

 

Originally, the manufacturers beat the piņas with large wooden mallets to break them up once they were soft and cool, then stomping on them like grapes to get the juices out..

 

Manuel Payno's work of 1864 describes the process:

 

After this the cooked hearts are taken to the crusher where they are broken up, mashed and squeezed by a variety of imperfect methods. The most common approach is to beat the material with huge wooden clubs, before trampling it to release the juice.

 

Producers soon moved to the tahona, a giant grinding wheel that can weigh up to two tons, operated by mules, oxen or horses (nowadays more likely by a tractor) and pulled in a circle in a cobble-stone-lined pit. Some distillers still use a tahona, but few use it exclusively.

 

As the tahona crushes the agave, the fibres are separated from the juices. Eventually the workers have to get into the pit and use pitchforks to remove the fibres, before the juices are drained off. The waste fibre is called bagaso, and may be used for compost, or fuel, and rarely for paper or textiles.

 

Some producers will take some of the crushed fibre from the tahona pit and add it back to the fermentation tank, to give the wort more agave flavour.

 

Modern distilleries use a mechanical crusher, or shredder, like a giant wood-chipping machine to process out the waste bagazo (the agave fibres, usually given away as animal food or used as fertilizer on the fields). This machine was first introduced to mill sugar cane for rum and aguardiente production.

 

Using one of these methods, the piņas are minced, washed with water and strained to remove the juices (called aquamiel, or honey water), them mixed with water in large vats. Many of these crushers process the fibres four times in a single line, separating all available juice from the fibres.

 

Some of these shredding and crushing machines are smaller - the crusher at Partida is a one-step machine. Each step presses and washes the agave, adding more water to the juice and diluting it.

 

Some distillers have experimented with other technology, including a grape-crushing machine, imported from France, at Tequilana. To date, no technology has proven superior to that already used to crush and shred the cooked agave, but the search is not over.

 

United States Patent 20020119217 shows a system to try and get sugars from the leaves of the agave for further fermentation into tequila:

 

The leaves of the blue agave plant, heretofore considered as waste, are processed to produce additional tequila by a process comprising reducing the size of the leaves, mixing with water, macerating the tissue by physical force to release sugars from the leaves, and subjecting the leaves to alcohol fermentation, either alone or in combination with tequila production from the piņa of the blue agave plant.

 

However, this does not seem to require cooking to covert the starches (inulin) in order to convert them to fermentable sugars, but suggests this can be done by enzymatic conversion (using inulinase to break down inulin to fermentable sugars). However, one study suggests, "fructans from A. tequilana Weber var. azul are not an inulin type as previously thought."

 

 

Sources:

• Molecular structures of Fructans from Agave tequilana Weber var. azul
• Visit to an old distillery

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