Coffee is one of the most popular drinks in the world and is made using the seeds of a vigorous shrub or small tree. These produce small, red-purple, cherry-like fruits, each of which usually contains two seeds – the coffee beans. Around one in ten contain a single seed, which is smaller and rounder, and known as a peaberry.

There are two main species of coffee: arabica and robusta, which cannot cross-breed as they contain a different number of chromosomes.

• Arabica coffee beans account for three-quarters of those grown, and are elliptical shaped, with at least twice as many oils and sugars as robusta; this makes them more aromatic, nutty and sweet.
• Robusta coffee beans are smaller, rounder than arabica beans, and have a stronger more bitter flavour. Sometimes described as tasting burnt or rubbery, they are preferred for making the classic, Italian espresso blends.

After harvesting, the coffee ‘cherries’ are either sun-dried and then hulled to remove the seeds, or the fruit pulp is removed first (using water and enzymes) before drying the seeds in the sun. The resulting, lightly coloured green coffee beans are then roasted, at between 180 and 240 degrees C for 2 to 20 minutes, to enhance their flavour. The higher the temperature and the longer the roast, the darker and more intense the taste.

Caffeine and polyphenols

Coffee beans contain over 1000 biologically active compounds, of which caffeine and a type of polyphenol known as chlorogenic acids (CGA) are the most studied for their health benefits.

Green coffee beans have the highest content of both caffeine and CGA. Green robusta beans contain almost twice as much caffeine as arabica beans (2.7% versus 1.5%) and chlorogenic acids – typically around 10% of their dry weight compared with 5% to 8% for Arabica coffee.

Once the beans are roasted, their level of CGA falls by half within 12 minutes, and virtually disappears after 20 minutes. The amount present in filter coffee therefore varies from 87 to 212 mg/100ml, depending on the coffee variety.

This still leaves the caffeine, of course, which only falls a little with roasting (to around 1.3%). And, while the highest level of CGAs is found in green coffee beans, roasting converts some of these into chemicals called quinides that reduce blood glucose levels and appear to reduce the risk of type 2 diabetes.

Coffee is good for your health

Most of us love coffee for its taste – the wellness benefits are an added bonus. To connoisseurs, the nuances of flavour in different coffee blends is akin to the complexities found in wine. These flavours and aromas depend on where the coffee beans are grown, how they were harvested, the roasting process and even the water used to prepare your brew. Some prefer the strong, tangy robusta blends, while others always opt for aromatic arabica blends.

The World Atlas of Coffee by champion barista and coffee roaster, James Hoffmann, explores the different origins of coffee country by country, from Bolivia and Burundi to the Yemen and Zambia. If you want to know the difference between Arabica and Robusta, how to tell if your beans are fresh or stale, the best way to grind them, and exactly how to use a French Press, Filter or Espresso Machine, this is the book for you. I’ve given it to several people as a present – the illustrations are fabulous. Available from Amazon.co.uk and Amazon.com

Coffee and weight loss

The caffeine and CGAs in green coffee extracts have several actions that suppress appetite and boost your metabolic rate so you burn more fat and generate more heat. These effect can raise your metabolic rate by as much as 10% for two to three hours.

In one study, regular ingestion of caffeine caused lean individuals to burn an additional 150 kcals energy over a 12 hour period, while obese volunteers burned an additional 79 kcals.

The CGAs in coffee also slow glucose absorption, and regulate the release of gut hormones which reduce hunger. If you have difficulty losing weight, drinking coffee and/or taking green coffee extracts may help.  

Click here to read my post on green coffee extracts and weight loss

Coffee and health

Large, population-based studies involving over 400,000 people suggest that drinking coffee is associated with reduced mortality from all medical causes, including heart attack, heart failure, stroke and some cancers (oestrogen-receptor negative breast cancer, endometrial, prostate, liver and bowel cancers). Regular coffee intake is also associated with lower risks for diabetes, heart failure, fatty liver disease. The greatest benefits come from drinking 2 to 4 cups per day.

A study involving over 90,300 US adults who were followed for around ten years compared mortality rates in coffee drinkers with those who drank coffee rarely, if at all. After adjusting for smoking and other confounding factors, those who drank 1 cup coffee per day were 6% less likely to die during the course of the study than non-drinkers. Having 2 to 3 cups per day was associated with an 18% reduction in mortality, while 4 to 5 cups coffee per day was associated with a 21% reduction in mortality. Those who drank 6 cups per day were 16% more likely to survive during follow-up than non-coffee drinkers. Findings were similar for decaffeinated coffee, suggesting that other coffee components, such as the polyphenols, were providing the main benefits. The greatest reduction in deaths was seen for heart disease, chronic respiratory diseases, diabetes, pneumonia and influenza, self harm, but not cancer. The researchers suggested that coffee may reduce mortality through beneficial effects on inflammation, lung function, insulin sensitivity, and depression.

Coffee and diabetes

In a study involving over 13,500 Japanese adults, men and women who drank one cup coffee per day, or more, were around 30% less likely to develop diabetes than those who drank little or no coffee, suggesting that regular coffee consumption protects against diabetes.

Coffee and your circulation

A study involving over 25,100 adults found that higher coffee consumption was associated with a lower rate of hardening and furring of the arteries, and reduced arterial stiffness. Those who drink from one to five cups of coffee per day had significantly lower levels of calcium build-up in their coronary arteries, after taking other confounding factors into account such as age, smoking status, alcohol intake, body mass index, blood pressure, diabetes and cholesterol levels.

While caffeine can produce a short-term increase in blood pressure, this effect tends to reduce with regular intakes. The chlorogenic acid in green coffee appears to reduce blood pressure by improving arterial elasticity.

The best coffee machines

To enjoy coffee at its best, and to obtain the highest levels of beneficial polyphenols, grind your own from whole beans as and when you want them, and aim to use them within 3 weeks of roasting, if you can. That means buying your beans ‘little and often.’ We have ours delivered by post every 2 weeks. A wide range of Arabica (aromatic) and Robusta (robust espresso) blends are available on Amazon.co.uk and Amazon.com which makes this easy.

The Bodum Electric Coffee Grinder lets you prepare up to 60g coffee beans to use as freshly as possible in a cafetière or French press.  as you need them. Available in black, red, lime green or off white, the transparent lid lets you select the right degree of coarseness. Available from Amazon.co.uk and Amazon.com

For making a single mug of quality coffee, the AeroPress is difficult to beat. Using gentle air pressure it creates a smooth, rich coffee every time, and has many rave reviews. Available from Amazon.co.uk and Amazon.com

The Sage Barista Express Coffee Machine, by Heston Blumenthal, is the best home machine I’ve ever bought. We even take ours with us on holiday to Cornwall, as it is part of the family! With a built-in grinder, it produces great bean-to-cup coffee. Ours is still working perfectly after 4 years of making a minimum of 10 cups of coffee per day. The little black tool on the left of the machine is the pull-down, detachable tamper with which you compress the beans manually. Available from Amazon.co.uk and Amazon.com

I borrowed the Sage Oracle Coffee Machine and Grinder by Heston Blumenthal to write this review, and Wow! It was every bit as good as I expected. It automatically grinds, doses and tamps your fresh coffee beans for you. It then delivers water at a precise temperature for optimum flavour extraction, while limiting the maximum pressure to prevent bitterness entering your espresso. If you prefer an Americano/Long Black or cappuccino, it correctly textures your milk via a separate steam boiler for simultaneous and instant steam. This automates the two most intricate parts of making an excellent coffee – and is easy to use when still half asleep in the morning. When you add up how much you and your family spend on buying cups of coffee per day, multiplied by the number of days per year, this amazing machine could become a perfect investment – despite costing three times more than its little brother, the Sage Barista!Perfect for coffee connoisseurs.Available from Amazon.co.uk and Amazon.com

Monitoring your caffeine intake

European guidelines suggests that a total of 400mg caffeine a day from all sources should have no health consequences for healthy adults (limited to 200mg for women whoa re pregnant or breast-feeding). To put that into context:

• 60ml espresso contains around 80mg of caffeine
• 125ml instant coffee provides 65mg caffeine
• 125ml filtered coffee contains 85mg caffeine.
• 150ml tea provides 32mg caffeine
• 250ml standard can of energy drink provides around 80mg of caffeine (check labels)
• 330ml cola provides around 40mg (check labels).
• A 50 gram bar of dark chocolate provides around 25mg caffeine, while a 50g bark of milk chocolate contains around 10mg caffeine.

Click here to find out how to assess the effects of coffee on your blood pressure

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