Bean-to-cup coffee machines take a lot of the effort out of brewing a good-tasting espresso. The best espresso machines can often provide help with tamping, time how long it takes to extract a double shot, and even help you steam milk for the optimal texture and temperature.
However, when it comes to choosing how to grind the beans, even the best coffee makers usually leave you to your own devices, offering a numbered dial on the bean hopper, and the most basic instructions. That isn't great, because picking the correct grind size (known as "dialling in" the grinder) is one of the trickiest parts of making a well-balanced espresso. Getting it right can often be a case of much trial and error, and potentially waste a lot of coffee beans.
Well, not anymore, with Ninja's latest coffee maker, the Ninja Luxe Café, which I got to check out at a recent event in London. It's an all-in-one machine that can brew filter and cold brew coffee, and what impressed me most was its espresso function. Unlike almost all other bean-to-cup coffee machines, it handles the hard work of dialling in for you, and even adjusts grind settings on-the-fly throughout the day. As a trained barista, let me tell you, that's a big deal.
So why does grind size matter?
At its heart, making coffee is pretty simple: dissolving some of the chemical compounds from roasted coffee beans in water. However, some of those compounds dissolve more readily than others, and getting a good-tasting drink relies on extracting just the right ones. That's where it gets complicated.
Sour-tasting compounds (those that make your mouth water, sometimes in an unpleasant way) dissolve fastest. You want some of those, but if your coffee is only in contact with water for a short time, that's all you'll taste. In addition, your coffee will feel "thin" in your mouth, without much flavour.
Next, you have the chemicals that give your coffee a sweet flavor. You want plenty of these, so your coffee needs to be exposed to water for long enough to extract these – but not much longer.
That's because, finally, the coffee beans release bitter compounds. If the water is in contact with the coffee grounds for a long time, you'll end up with too many of these, and you'll end up with a drink that tastes nasty and leaves your mouth feeling dry.
To achieve the sweet spot and achieve a well-rounded flavor, pulling a double shot of espresso should take around 28 seconds. So how do you achieve that?
You do it by adjusting the grind size. If your coffee beans are ground coarsely, water will pass through them relatively quickly, reducing the contact time and extracting fewer flavor compounds. Grind them more finely, and it will take longer for water to find its way out. Plus, there will also be a larger surface area with which water will make contact, dissolving more flavor compounds from the beans.
That sounds simple in principle, but there are a lot of factors that can throw a spanner in the works, and there isn't one ideal grind size that will work for everything.
For example, how long it takes to pull a shot varies on the bean type (robusta or arabica) and variety, how it's roasted, and how old it is. For example, coffee beans lose carbon dioxide over time, which leads to faster extraction. So, the longer you've had them, the finer you'll need to grind them.
To make matters even more complicated, environmental factors such as temperature and humidity can affect how your beans behave, and if you've been using your coffee grinder a lot, it will start to heat up, which will also impact the results. Good luck if you're working by an open window, or under an AC unit.
To cut a long story short, it's complicated, so having a machine that can do it for you is an enormous time-saver.
How the Ninja Luxe Café does it
When you're dialling in a coffee machine yourself, you'll start by picking a grind size close to what you think will be correct, then seeing how long it takes to pull an espresso – and that's pretty much what the Ninja Luxe Café does.
It begins with a moderate grind size, then extracts a double shot and times how long it takes. If it happens to be the ideal time, then it recommends you go ahead and stick with it. If it takes too long, the machine moves the grinder burrs a little further apart to make the grind size coarser, then timing another shot. If the water runs through too fast, it will move the grinder burrs closer together for a finer grind.
Of course, this is great; but what impressed me the most is that the machine will also carry out adjustments throughout the day to make sure your coffee tastes consistently good, no matter when you have a cup.
Consistency is the gold standard in coffee-making, but as your beans age, their properties will change and the grind size will need adjusting to compensate. The Ninja Luxe Café will do that for you.
That means you can brew your morning cup of coffee, have another at lunch, then make espresso martinis for friends in the evening using the same beans without worrying about your brew starting to taste off. I'll certainly drink to that.
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