# Natural Processing (/en/docs/foundation/phase-2/chapter-09)
## Phenomenon [#phenomenon]
In some origins, at harvest time, hillsides fill with mesh tables about a metre off the ground, each covered with a layer of red coffee cherries. A few weeks later they have turned dark brown and wrinkled, like raisins. Grab a handful and shake it, and you can hear the seeds rattling inside.
This is the natural process: the whole cherry dries intact. It is often described as intensely fruity, sweet, a little winey. That is how the coffee trade often describes specialty naturals.
But you may also meet a different kind of natural: muted, like fruit left out overnight, maybe slightly musty. And some naturals taste of nuts and chocolate, with hardly any fruit at all. Same name — why such different cups?
## Variables [#variables]
Natural processing looks like the simplest method: pick, spread, dry, hull. But every step involves a decision:
| Variable | What it is |
| -------------------- | ------------------------------------------------------------------------------ |
| Ripeness and sorting | Whether unripe, overripe or insect-damaged cherries were removed before drying |
| Layer thickness | A thin single layer, or a deep pile |
| Drying surface | Raised mesh beds, a concrete patio, tarps on the ground, or a mechanical dryer |
| Turning | How often, and how evenly |
| Weather | Sun, humidity, rain, overnight dew |
| Drying time | From a few weeks to longer, depending on all of the above |
Once fully dry, the dried cherries are usually rested for a while, then hulled by machine, removing the dried skin, pulp and parchment in one go (Chapter 12).
## Experiment [#experiment]
Thought experiment: split one day's batch of ripe cherries in half and dry both halves in the same weather.
* A: a thin layer on a raised mesh bed, turned several times a day;
* B: a thick pile on the ground, rarely turned.
Which half dries faster and more evenly? If you dig into both piles after a week, what do you expect to find at the bottom of B? Will the two halves end up tasting the same?
Second experiment: another batch, where a fifth of the cherries were picked green and never sorted out. Dry them using method A.
Once dry, the green cherries and the ripe ones are all dark brown and hard to tell apart. Will the unripe cherries disappear into the "natural fruitiness"? Or will they stay in the cup?
## Observation [#observation]
In the first experiment, A usually dries faster and more evenly. The bottom of B stays wet and stuffy; air cannot reach it, and when you dig in it is often warm, sour-smelling, even spotted with mold. Thin layers, frequent turning and raised, ventilated beds are the most common controls in natural processing.
Researchers who followed natural processing from start to finish found that bacteria were most numerous at the beginning, while the cherries were still very wet; yeasts became more common as the fruit fermented and dried; and among the molds, Aspergillus was the most abundant, alongside Penicillium, Fusarium and others. The acetic and lactic acids measured in the seeds may have come from microbial activity.
Mold is the thing to watch most carefully. Whole cherries hold enough water that, in humid tropical weather, the outer layers can grow mold and produce ochratoxin A (OTA) during the first three to five days of drying. Most of the mold and toxin ends up in the husk removed at hulling, but that is no substitute for good drying. This kind of contamination can be greatly reduced by good agricultural practice and proper drying, grading, transport and storage.
Second experiment: unripe cherries do not vanish. The green, astringent notes that unripe cherries bring often stay in the cup, and natural fruitiness does not cover them up. Worse, once dry they are harder to sort out than when they were fresh. That is why ripeness at harvest (Chapter 6) matters especially for naturals.
## Model [#model]
### A race between drying and microbes [#a-race-between-drying-and-microbes]
Once the whole cherries are spread out, two things happen at the same time:
1. Sun and wind are taking water away;
2. Microbes are eating the sugar in the pulp, and multiplying.
The less water there is, the harder it is for microbes to grow. So natural processing is a race: drying has to be fast enough to stop the microbes before they go too far — but not so fast that it overshoots (Chapter 12). The most dangerous stretch is the first few days, when the cherries are wettest and sweetest. Hit a run of rainy days, or pile them too thick, and the race is lost.
### The fruit stays with the seed the longest [#the-fruit-stays-with-the-seed-the-longest]
Compared with washed coffee, the seed in a natural spends the longest time with its fruit. During that time:
* microbes ferment the fruit, producing acids, alcohols and other compounds;
* the seed itself is still alive, and its germination-related metabolism peaks about a week into natural processing (Chapter 7);
* natural green coffee ends up higher in glucose and fructose than washed.
Where do the fruitiness and heavier body of naturals come from? A common explanation is that "the flavor of the fruit soaks into the seed". A more careful answer is that how much of what the microbes make gets into the seed, and how much of it survives roasting, is not yet clearly known. Changes in the seed's own metabolism may matter as much as anything coming in from outside.
### Natural is a condition, not a flavor [#natural-is-a-condition-not-a-flavor]
The natural process specifies just one thing: **the seed dries inside the whole fruit**. Under that condition:
* ripe picking, careful sorting and even drying often give a clean, sweet, fruity cup;
* mixed ripeness, slow drying or rain partway through can give an over-fermented, muted or moldy cup;
* many regions use natural processing as a traditional, low-water method for large volumes, not necessarily aiming for fruitiness, and those coffees often taste more of nuts and chocolate.
Naturals often have more ripe-fruit aroma and a heavier body than washed coffees from the same origin — still just a starting point.
## Transfer [#transfer]
In the [Processing Mill](/world/processing) scene you can choose the natural pathway and watch the fruit stay around the seed until it is fully dry. When reading a bag:
| On the bag | What you can reasonably infer | What you cannot infer |
| --------------------------------- | --------------------------------------------------- | ---------------------------------------------------------------------------- |
| Natural, dry process | The seed dried inside the whole cherry | That it will be fruity; that it is free of defects |
| Raised beds, African beds | It dried off the ground, with better airflow | How evenly or for how long it dried |
| Slow-dried, shade-dried | The producer slowed drying on purpose | How slow; that slower is better |
| Strawberry, boozy, tropical fruit | The roaster's impression of this lot | That your cup will taste like that; it may also be a heavily fermented style |
| Anaerobic natural | Some step happened with limited oxygen (Chapter 11) | Exactly how it was done |
Some people love the intensity and wineyness of naturals; others find them too much. That is preference, not right or wrong. But keep two things apart: whether you like a style, and whether a particular cup has a defect (Chapter 35).
## Misconceptions [#misconceptions]
**"Naturals are always fruity."** "Natural" only tells you the seed dried in its fruit. Ripeness, sorting, the speed and evenness of drying, variety and roast all change the result. Plenty of naturals taste of nuts and chocolate, and some taste muted because they were handled badly.
**"The stronger the boozy, fermented taste, the better the processing."** Strong booziness and ferment can be a deliberate style — or a sign of over-fermentation. Intense is not the same as good, and liking it is not the same as it being defect-free.
**"Natural is the simplest method, so it is the lowest quality."** It has fewer steps, but it is very demanding about weather, spreading and turning. A well-made natural can be a very clean, very refined coffee.
**"Natural fruitiness is just the fruit's flavor soaking into the seed."** It is a common intuition, but the actual pathway has not been worked out, and the seed's own metabolism is changing its composition too.
## Real Lab [#real-lab]
There is no registered lab card for this chapter. Here is a kitchen analogy for feeling the difference that layer thickness and airflow make.
**You need**: a bunch of grapes (or cherry tomatoes), washed and patted dry; two plates and a bowl.
1. Lay half the grapes on a plate in a single layer, not touching, by a bright, airy window.
2. Pile the other half in a bowl in the same room.
3. Check once a day for five to seven days. Note: which batch wrinkles more evenly? Which one first goes soft, leaks juice, smells sour or grows mold spots? Where does the mold appear — where grapes touch each other, or at the bottom of the bowl?
4. Write your predictions down first, then compare.
**Caution**: look, do not eat. Do not lean in to sniff anything moldy, and clean the plates and bowl thoroughly when you finish.
Then do a real tasting: if you can buy two naturals from different roasters, brew both with the same recipe (Chapter 24) and try to describe whether the fruit is "clean ripe fruit" or "muted, like fruit left out overnight", and whether the body feels heavy or light. You will find that a lot of difference hides under the single word "natural".
## Check Your Model [#check-your-model]
**Predict.** A farm is trying natural processing for the first time. They pile the cherries more than ten centimetres deep on a concrete patio and turn them every two days. A week of overcast, rainy weather arrives. What problems do you expect? What could they change first?
Piled too deep and turned too rarely, the cherries at the bottom cannot breathe; add rain, and they stay wet far too long. Expect over-fermentation, heating and possibly mold, raising the OTA risk, with a cup that is muted, sour and musty. What to change first: spread thinner, turn more often, move to raised, ventilated beds, cover the coffee when it rains, and sort out unripe and damaged cherries before drying.
**Diagnose.** A natural smells lovely when you open the bag, but the brewed cup tastes green and astringent, with no obvious musty or vinegary note. Which step is the most likely cause?
Green and astringent points toward unripe cherries mixed in at harvest and not sorted out before drying — once dry, they are hard to tell from ripe ones. Also consider a very light, underdeveloped roast, and underextraction during brewing (Chapter 23). Try the same beans with a different recipe first to rule out brewing.
**Explain.** In your own words, explain why the first few days of natural processing are the riskiest.
In the first few days, the cherries are at their wettest and their pulp holds the most sugar — ideal conditions for microbes — while drying has only just begun and the water has not come down yet. If it rains, or the layer is too thick, or turning is neglected, the microbes get ahead of the drying and the coffee over-ferments or molds. As water drops, microbes find it harder and harder to grow, and the risk gradually falls.