Dark roast isn't strong. Say what?

You want a coffee that actually wakes you up. So you buy the darkest bag on the shelf, and get a cup that's more bitter but leaves you no more awake.

A recent Reddit thread asked for something stronger than a blend sold as "Industrial Strength", and several replies made the same point.

Dark roast tastes stronger, but it isn't more caffeinated.

Roast changes the flavour, not the kick

Roasting longer brings more bitterness and body. It barely moves the caffeine. One lab study measured about 1.13% caffeine in a light roast, 1.17% in a medium and 1.08% in a dark. In your cup, that difference disappears.

The bean is what matters

Most specialty coffee is arabica. Robusta, the other main species, carries close to twice the caffeine: around 2.2% of its weight against about 1.2% for arabica, according to CoffeeGeek.

Will it taste burnt?

On its own, robusta tastes heavy and bitter. That's why it usually turns up as a small part of a blend, mostly espresso blends built for milk, where the extra body helps. If you drink your coffee black, look for a blend where robusta is a small share, or stay with arabica and use more of it (see below).

Why it's hard to find

Of the 15,000+ coffees we track, fewer than 10 mention robusta in their name or description. Some blends use it without saying so on the front of the bag, so check the list of origins. Darkstar's Zuri, for example, is Brazil and PNG with Indian robusta.

Not sure you'll like it?

Buy the smallest bag first. A kilo of coffee you don't enjoy is an expensive mistake, however good the discount.

What to look for

• A blend that names robusta in its origins.
• Espresso blends built for milk, where the extra body helps.
• More coffee per cup, if you'd rather stay with arabica. A stronger ratio does more than a darker roast.

Our picks below are three blends with robusta in them, with whatever offer each roaster is running right now.