Filtered coffee is the most common method of preparation in many places, including the US and Scandinavia.
Boiled coffee in this case refers to an alternative method of coffee preparation, in which coarse ground coffee is simply added directly to boiling water and left to brew for a few minutes.
In a recent study from the Chalmers University of Technology and elsewhere, researchers found that coffee can help reduce the risk of developing type 2 diabetes — but only filtered coffee, rather than boiled coffee.
They found that the choice of preparation method influences the health effects of coffee.
The study is published in the Journal of Internal Medicine. One author is Rikard Landberg.
Many previous studies have shown a connection between high coffee intake and a reduced risk of developing type 2 diabetes.
In the study, the team used data from a group of Swedish people and was collected in the early 1990s.
They used a novel method to help differentiate between the effects of filtered coffee and boiled coffee.
The researchers found specific molecules — ‘biomarkers’ — in the blood of those taking part in the study, which indicate the intake of different sorts of coffee.
They found that people who drank two to three cups of filtered coffee a day had a 60% lower risk of developing type 2 diabetes than people who drank less than one cup of filtered coffee a day.
Consumption of boiled coffee had no effect on diabetes risk in the study.
Many other types of coffee preparation were not specifically investigated in the study, such as instant, espresso, cafetière, and percolator coffee.
But given that espresso coffee, from classic espresso machines or the now popular coffee-pods, is also brewed without filters, the team believes the health effects could therefore be similar to boiled coffee, in terms of the risk of type 2 diabetes.
Coffee made in a cafetière, or French press, is prepared in a similar way to boiled coffee, so it may also not have the positive effect of reducing type 2 diabetes risk.
It is unclear whether instant coffee, the most popular type in the UK, would be more similar to filtered or boiled coffee in this respect.
The researchers also stress that the health impacts of coffee do not depend solely on if it is filtered or not. They also vary with how the coffee beans, and the drink in general, are managed.
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