Spice is a vast and complex subject that touches every aspect of the Dune universe. With the film imminent, why not take the opportunity to talk about it? Frank Herbert's works have inspired other great franchises, one of them Star Wars, and their modernity even after some time makes them still noteworthy today. The parts full of spoilers for those unfamiliar with the saga will be marked as such and absolutely avoidable.

La Spezia

The spice, also called Melange, is a drug of biological origin, with the taste and smell of cinnamon, which is part of the life cycle of the Sandworm. It is undoubtedly the most important and expensive substance (nootropic) in the whole universe, capable of bending empires and necessary for the normal performance of many daily activities.
Frank Herbert has never been very precise on the description of the spice, whose color should be between orange, brown and sand, but we know from the mouth of one of the protagonists of the novels that, when illuminated with artificial light sources, it shines of blue light.
Spice is also the most expensive substance in the universe. At the beginning of the story of the first book of the Dune cycle, the melange is sold for 620 thousand solar (the currency of the empire) per decagram.

ArtStation - DUNE Spice Crawler, Benjamin Last

Method of recruitment 

In the Dune universe, spice can be taken in many ways, the most common of which is by mixing it with food. By inserting a small amount in every food or drink, you can take it practically without noticing it at all. Some people use it more heavily, as it remains a full-fledged drug, and as such it has profound consequences on the body.
The immediate consequences are an increase in awareness of the surrounding space, with the senses that are heightened and health that improves. In some genetically predisposed individuals, the spice unlocks foreknowledge capabilities, during which it is possible to glimpse the future.

Long-term consequences

Taking a small amount of the spice per day, even mixed with meals, potentially extends human life by centuries. Those who use it particularly and intensively will notice first the iris and then the rest of the eye take on a pigmentation close to dark blue, forcing them to reveal the truth with a single glance or to use contact lenses.
However, these benefits do not take into account the enormous price to pay. As a drug, the spice is highly addictive that can kill you with excruciating pain if you don't take Melange for a long time. The choice is therefore simple: approach the divine with the spice or die in excruciating suffering.


Spice extraction

The spice can only be extracted on the planet Arrakis since only on that planet the Sandworm has an ecosystem suitable for its survival. If transferred to other planets, the creature does not survive and produce no spice. Throughout history, several attempts have been made to break Arrakis' monopoly on the spice but, unfortunately, all have failed.
Once a spice field has been found, a gigantic aerial vehicle called a "wing" transports a "harvester" to the site. The harvester sifts the sand and retrieves the melange present in the area. The rhythmic noise of the ladybug-shaped machine attracts the Sandworms and forces them to flee. Around each harvester are a ready-to-go wing and three reconnaissance ornithopterans to spot the arrival of the Sand Worm.
The Fremen, the indigenous people of the planet Arrakis, walk on the sand and have learned to hand-pick the spice, avoiding the wrath of Shai-Hulud.

The Space Guild

In addition to "personal" reasons, the melange is also used by the navigators of the Space Guild to allow a safe journey through the dangers of the cosmos. In order to allow the existence of navigators, these individuals must be kept in constant contact with the spice without ever separating from it. Unfortunately, this slow and inexorable process transforms their bodies and minds into something very far from the human being.
Since the Space Guild is the only one, with its ocean liners, to allow movement between the systems of the universe, the spice is fundamental and whoever controls the spice controls the universe.

Spoiler: Origin of the spice

In reality, the process of making the spice is a bit more complicated than one might think. The Sand Trout, which are the main desertificers of the Dune universe, collect the water present in the subsoil and accumulate it together with a fungal secretion. This process, combined with pressure and carbon dioxide, cause a violent explosive eruption which, when dried by the Arrakis sun, creates the spice.

Spoiler: Access to genetic memory

The Bene Gesserit sisterhood over the centuries has devised a test, called the agony of the spezzia, to allow a novice to access the memories contained in her own DNA and make her become a reverend mother. Although it bears the name "essence of the spice", the substance involved has nothing to do with it.