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Indonesian Wet Hulled Coffee: Your One-Stop Guide

Ever heard of wet hulling? If you have, did you wonder what on earth it actually means and what it has to do with coffee?

Would you be interested to hear how it enables coffee production in a country with 70-90% humidity all year round; typhoons; and, in some places, typically 2,000 mm of rainfall a year? Or what about how it creates a high risk of defects—but a rich and strong body?

If you answered yes to any of those questions, this article is for you. We’re going to cover everything you need to know about the Indonesian method of wet hulling, its pros and cons, and how it affects both roasters and baristas.

So What Actually Is Wet Hulling?

Before any coffee can be roasted and consumed, it goes through a processing method that converts it from a fruit to a dry green bean. There are many different ways to do this, but the main three are natural; washed, or wet processed; and honey. Don’t confuse wet hulling with wet processing, though!

Wet hulling, or giling basah, is the traditional method used in Indonesia. And although both the name and the method are very similar to wet processing, the cup characteristics are incredibly different.

How Does Wet Hulling Work?

Inside every coffee cherry is a bean, a layer of parchment, and a layer of mucilage (along with a few other layers). Hulling itself refers to the removal of the parchment from the bean—but to fully understand wet hulling, we should look at the whole process.

The first step is to remove, or pulp, the beans, which are still coated with that parchment and mucilage, You then ferment them in concrete water tanks or plastic rice bags overnight. This helps break down the pectin in the mucilage, which makes for easier removal.

We remove the mucilage by washing the beans. This usually happens the following day, but it depends on the water supply at the farm. If there’s an insufficient amount of water, then the coffee may be sold to a larger processing mill in the area where they will continue the process.

Once the mucilage is removed, you then have what’s known as a wet parchment coffee, i.e. the coffee bean is covered in a wet parchment layer. It’s then sun dried in its parchment for 2-3 days—no more! The moisture content will have reached about 20-24%, leaving the bean at the required hardness for hulling.

Up til now, there’s been very little difference between the wet and wet hulled methods. For wet processed coffees, the beans would continue to dry until around 11% moisture. This would leave the parchment layer brittle and, as of such, easy to remove during the hulling process.

Yet at 20-24%, the bean itself is soft to the touch and inflated with water, while the parchment is semi-dry. So to finish this wet hulled coffee we have to put the coffee through a huller that’s specially designed to handle semi-dried parchment. What’s the difference? Well, this kind of huller requires more power, since removing the parchment requires more friction.

Hulling this semi-dry parchment isn’t as clean a process as dry milling. The high moisture content means the parchment clings to the bean, making it harder to remove than with other processing methods. Normally pieces of parchment will still be left on the beans, whose pale-green colour shows that they’re still wet.

As of such, you need to be really careful at this point. The coffee is so wet and soft that if you were to poke it firmly with your finger it would be crushed. There’s a high risk that the machinery that hulls the coffee will also split it at the ends, due to the bean’s low density. This is called kuku kambing or goat’s nail, reflecting its shape.

Kuku kambing visible on wet hulled coffee

‘WetHulledKuku’, Kuku kambing visible on wet hulled coffee. You can see its similarities with a goat’s nail.

The hulled beans are then dried to 12-13%. They are left in the sun during the day, but stored in bags inside over night to continue fermentation. The sun drying will take a few days, but afterwards, the beans are ready for export. You can recognise ready-for-export wet hulled coffee by the bean’s dark green and patchy colour. Some even call it blue.

So Why Do Indonesian Farmers Wet Hull Their Coffee?

There are two reasons why wet hulling dominates in Indonesia: history and geography.

Coffee was first introduced to Indonesia by Dutch colonists in 1699, whose purpose was financial gain. From their profit-orientated perspective, every day the coffee remained on the farm was money lost. Since wet hulled coffee take several less days to dry, they were able to see returns quicker—and for less labour.

Yet even had the Dutch not taken this position, they would probably have resorted to wet hulling. Drying coffee beans in the intense humidity of the country can be a problem. In a warm climate, it takes at least 2-3 weeks to dry an average coffee. In most parts of Indonesia, where rainfall and humidity are high, it would take far longer. Bacteria would cause coffee defects long before the beans would be at a low enough moisture content to dry. Remember, coffee is usually dried in at least its parchment—which protects it from damage and promotes consistency while the bean is drying. Yet wet hulling removes the parchment so the sun and heat can directly penetrate the bean, therefore allowing it to dry 2-3 times quicker.

average rainfall diagram
average rainfall diagram

Graphs display the average rainfall in Bandar, Indonesia compared to Sidamo, Ethiopia. Highlighting the all year round wet climate of Indonesia. Credit:

What Profile Does Wet Hulled Coffee Have?

Wet hulled coffees are known for their extremely rich and strong, syrupy body, but devoid of sweetness and with a really low acidity. They may have a slight tobacco profile, but when I think of wet hulled coffee, I think of average, inconsistent flavours.

But why is wet hulled coffee like this?

For a start, the method is so quick and harsh that you can get defects. On top of that, quality equipment is so scarce, and beans are often dried on concrete patios, dirt tracks or even roads—certainly not the best conditions for drying coffee.

For some coffee-producing countries, increased demand for specialty coffee is driving a transformation of methods; not so in Indonesia. Most Indonesian coffee is used for blends, and is also sold to commercial coffee shops where middle-of-the-road coffee will suffice. As of such, there’s little financial reward for producing quality coffee.

Yet there are some exceptions. A slowly increasing number of farms, especially in Sulawesi and Sumatra, are beginning to take increased amounts of care of their coffee beans.

'WetHulledDefect' on coffee beans

‘WetHulledDefect’, a small collection of beans, but a large variety of defects.

Roasters: What Does Wet Hulled Processing Mean For You?

For roasters, the big question is why. Why should we roast a wet hulled coffee when it tends to be so unbalanced and so full of defects?

The answer: body. These coffees are highly sought after, since a small amount of them will seriously boost the body of a blend. Even as a mere 10% of a blend, it will have a big impact on the flavour. Be careful, though: too high a percentage of wet hulled coffee will create a muddy, even dirty, taste. Make sure you experiment with the proportions to find the perfect ratio.

Wet hulled coffees are slightly harder to roast, as well. One of the most important parts of roasting coffee is dehydrating the beans to ensure they can reach first crack at an appropriate time. Wet hulled beans tend to have a moisture content of around 10.7%-11%, if not more. This is about an extra 1% moisture than other coffee methods, so you’ll need to heat the the coffee a little bit more towards the start of the roast. If you don’t dehydrate your wet hulled coffee sufficiently, you’ll end up with a coffee that tastes inconsistent, astringent, unbalanced and sour—not exactly an ideal coffee profile.

This is particularly important to keep in mind for roasting blends. You’ll need to take the coffee about a degree or so darker to compensate for the moisture content of the wet hulled beans. For me, the easiest way around this is to roast all the different coffees individually as filter roasts. Then I make a filter from each of them at the same time, before blending them all together in a new cup. This is a great way to experiment with different proportions, as well.

Baristas: What Does Wet Hulled Processing Mean For You?

Baristas, keep in mind that wet hulled coffees are going to have a heavy body but only a little acidity or sweetness. Keep your temperature lower so you don’t burn the already heavy body. Don’t run your shots too long. And do your best to keep your flavours balanced, so as to highlight the strengths of the coffee.

Knowledge is power. It helps you to create that perfect coffee, and also, it helps you to get loyal customers. Most customers love to learn. If they’re the kind that ask questions, and you can explain all about the wet hulled coffee they’re drinking to them, they’ll come back more often—guaranteed!

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