The bean that could change the taste of coffee

The seedlings, he says, will simply die in the heat.

"We have an extended drought season," he explains. "We are used to two rainy seasons, the short rains and the long rains. Right now, you cannot say when the short rains are coming."

Mr Kinyua, a member of the Mutira Farmers Cooperative in Kenya's Kirinyaga County, adds that higher temperatures attract more pests and diseases, raising the cost of protecting his produce.

Asked if he has ever felt at risk of not making enough money to get by, he says unequivocally: "Yes, I've felt it many times."

What's happening on Martin's farm is an insight into the danger the coffee industry is in.

Arabica, the species Martin grows, accounts for the majority of coffee beans traded globally, some 70%. But it is highly sensitive to changes in both temperature and humidity. For the last two years, production has failed to meet demand.

BBC World Service - Business Daily, Coffee- Time for a new bean

The industry is now pinning hopes on another coffee species to sustain production - liberica. Native to western and central Africa, commercial cultivation is centred on the Philippines and currently accounts for only 2% of the global coffee bean harvest.

With a tougher bean that's tricky to process, and perceived as producing a less desirable flavour, liberica is now gaining renewed interest for its hardiness in changing climates.

In a hot and humidified greenhouse, Dr Aaron Davis parts the branches on a lanky plant to reveal a cluster of dark red berries.

This is Palm House at Royal Botanic Gardens, Kew, in London, which simulates a tropical climate. The red berries, known as coffee cherries, are what's processed and roasted to create the drink that's loved the world over.

Dr Davis' work has been carried out with increasing urgency in recent years.

Findings from a recent study suggest that if global temperatures rise 2°C, countries supplying a quarter of the world's arabica will suffer major declines in yield. A rise of 2.5°C will have this impact on 75% of supply.

"We need additional coffee crop species that are able to grow under altered conditions," he says. "And what we're seeing is that liberica coffee is more climate resilient than arabica."

On the question of what happens if the coffee market doesn't adapt, Dr Davis says soberly: "We're going to have less coffee and prices will go up, but the real hit and the real jeopardy is for farmers."

The outcome of all this could be that the product in our coffee cups is transformed.

Romulo, a Filipino café in west London, serves barako coffee - made from a blend of liberica and arabica beans. It's traditional in the Philippines.

"When we were growing up in the Philippines it was prestigious to have Nescafe, and the common man, we drank barako coffee," says owner Chris Joseph.

In front of him, Mr Joseph has scattered a mix of arabica and liberica beans onto a plate. The liberica are almost twice the size, about a centimetre long, and aesthetically more uniform than the arabica.

"For me, liberica is sweet-ish. And maybe nutty as well," says Mr Joseph.

Liberica has in the past been considered an inferior crop to arabica. Its large beans are harder to harvest and process due to their thick skin and pulp, and the taste is widely regarded as more bitter.

Like the world's second-most traded coffee bean, robusta, it is considered more of a supplementary species than the main act.

However, Dr Davis, and colleagues in Uganda and South Sudan, are focusing on a type of liberica with a smaller bean - called excelsa - which they believe has an improved flavour profile.

Regardless, the spread of liberica may not be a matter of popularity, but necessity.

Coffee traders, middlemen connecting farms to retailers, are under immense pressure to meet rising demand. Volcafe is one of the world's biggest traders, handling roughly 600 million kilograms of coffee a year.

"We've seen global coffee consumption generally in the last decade increasing at a rate of 2% per year," says Hannah Rizki, global head of research.

At the same time, Volcafe's projection for the coming year is "an unprecedented third consecutive deficit" in production. Ms Rizki explains: "Supply has been below demand, and when that tends to happen, global stocks are drawn down. We're expecting those stocks to continue to fall."

On the prospect of liberica making up the shortfall, she believes there is "huge potential".

"It's a case for governments to get involved and promote different varieties, and also for the farmers to understand the varieties that they're growing."

Typically, it takes four years for a coffee plant to grow from seed to first crop. This represents a considerable time investment for farmers new to the species, and risk - fruitfulness is not guaranteed.

But liberica is already being embraced by the International Coffee Organisation - the main intergovernmental body for coffee - as part of its mission to strengthen the industry.

Its executive director Vanúsia Nogueira, who grew up on a small coffee farm in Brazil, says the flavour of coffee will probably change with the addition of liberica so that the industry can meet demand.

Her primary worry is the livelihoods of farmers, because economic insecurity is "a continuing problem".

"There are many players in this game. Buyers try to manage the market as they think that will be good for them. But there is no chain if you don't have the producers."

Asked about how Volcafe pays farmers, Hannah Rizki says they "try to come to long term agreements with farmers or suppliers. Sometimes at a minimum price and sometimes fixed against the global benchmark price for coffee."

She stresses that Volcafe recognises it has a role in supporting farmers.

"It's a long term investment for the farmer, but it's also up to us to encourage that production and to give them a price incentive to try these new varieties."

"Without the farmers, we won't have a cup of coffee but we also won't have a business," she adds.

Yet back in Kirinyaga County, Mr Kinyua says low and volatile prices have left him unsure about his future in farming.

"I'm price-sensitive. Why should I not fetch a high enough price to ensure I produce regularly to sustain the market?"

-bbc