“Someone told me some time ago that coffee roasting is nine-tenths science and one-tenth witchcraft - it’s very true," said Jeremy Torz, co-owner of Union Hand-Roasted Coffee as we talk about the importance of knowing and nurturing your beans for the perfect roast.

Union is a speciality artisan coffee roaster based in east London where they hand roast coffee every day in small batches to display the coffee's fullest expression of flavour and aroma.

“When it comes to roasting I tend to look at coffee like photographic negatives – some pictures you see are very tonal, bold and emotive and there are other images that are very soft, subtle and gentle – I think of coffees in the same way – there are coffees with big personalities and character so they need a little bit more development, a bit more driving, a firm hand on the roaster, with a hotter roast, where as other coffees will need something a bit more gentle so not to override their delicate inherent characteristics. You really have to know your coffees, what potential it has and where it has been grown to inform how you roast it.

“You learn through experience. The most important thing for someone roasting coffee is to learn to critically taste it – if they can critically taste the coffee then they can relate that back into the roast. Every batch consignment we bring from origin we will do two, three or four test roasts, then taste those in detail, looking at times and temperature and then decide on the best way of roasting that particular coffee. It all comes down to the micro-climates in which they were grown and the way they were processed."

Union are returning to The London Coffee Festival this year with its ‘Roastery on Tour’ where visitors can experience the intensity of the roast first hand, as Jeremy and business partner Steven Macatonia expertly demonstrate their craft roasting in a vintage San Francisco Roaster. There will also be an origin themed espresso and brew bar and you can take part in a flavour challenge to test your senses.

Jeremy said: “The London Coffee Festival is a great environment for people to come and find out more about coffee and we want to give visitors a point of difference and a learning opportunity. “We are again roasting coffee live to demonstrate the roasting process and show how much of an artisan skill it really is.

“There will also be a taste challenge. When we talk about great flavours and nuances that coffees have, some of these flavours are really broad and bold, then some are more subtle, so what we will be doing is inviting people to take part in a challenge where they have three cups in front of them and they have to pick the odd one out against the clock. It’s a chance for people to participate in a tasting that replicates the way we taste coffee as professionals to evaluate and buy it. There will be prizes too.

“We will have a selection of our supreme micro-lots, which are coffees that are incredibly characterful with amazing flavours and represent small parcels from individual farms that may only be one or two sacks – coffee from where the sun, moon and stars all come into alignment on the day of harvesting.”

Watch pioneering duo Jeremy Torz and Steven Macatonia expertly demonstrate their craft in the ‘Soho’ area of the festival and sign up to test your taste buds in the flavour challenge. Visit Union's page in the What's on section to find out what time they'll be conducting live roasting demonstrations and what countries they'll be concentrating on each day...

Interview by Kay Lockett