He's the alchemist of the Covered Market. Graham MacDonald transforms Guernsey milk and other locally-sourced ingredients into smooth gelati; fruit, sugar, and water into creamy sorbets. His tools? A series of measuring jugs, scales, a refractometer to assess sugar content, the all-important calculator, and a spark of creativity. All this takes place in his lab-cum-shop iScream, which is Oxford’s first gelateria. MacDonald was first inspired by a vacation in Italy where the village gelateria was the gathering place for all ages at any hour of the day, and about a decade later, after many taste tests and equipment-hunting, he opened iScream, which has recently celebrated its second birthday.

At Tuesday night’s gelato tasting, MacDonald opened by passionately describing the story of acquiring organic, unhomogenized, Guernsey milk from Nick Gosling, who maintains a herd of named cows (there’s no Daisy, but there’s a Veronica). It is clear that MacDonald will not sacrifice quantity for quality, instead paying more for the local, organic, milk, produced by a dairy farmer who can tell the cows apart, and notices when an ill cow self-medicates by eating specific herbs in the Wiltshire pastures.

But before we sampled anything with milk, MacDonald had us try a spectrum of sorbets as a prelude to the richer gelati. Our colourful spoons dipped into rhubarb-ginger, apricot, peach, raspberry, lemon, blackcurrant, passion fruit, and mango. He had to keep assuring us the only ingredients were fruit, sugar, and water; there was no dairy, which was hard for some to believe given the creaminess of the sorbets. My personal favourite was the mango, which brought me back to the end of a Chef’s Whim tasting menu at Craigie on Main (Cambridge, MA). My brother and I were convinced we had been served slices of mango and we exchanged incredulous glances as to what was on our dessert plates - cold fruit or sorbet? I was pleased to find the same memorable mouthfeel and flavour here - it is like eating a smooth mango slice without the fibres.

Then came the ‘dessert’ of the tasting: a selection of gelati building up to MacDonald’s favourite flavour for everyday consumption: pistachio. He commenced by debunking stracciatella: it is not vanilla because it does not have vanilla extract in it; rather, it is pure dairy gelato with flecks of chocolate. This flavour was the perfect showcase of the creaminess of the milk from Gosling’s herd. MacDonald’s mention of chocolate and vanilla gelati was met by cheers from the tasting crowd: he uses Montezuma chocolate, which he also sells bars in the store, and “proper vanilla” essence that is £125 per litre, as well as ground vanilla pods. We tasted white chocolate with Kinder Bueno, one of the most popular flavors, but did not sample the bestselling salted caramel – he insisted we go to the Covered Market and try it ourselves. Before introducing the next gelato, he told us about an encounter with Raymond Blanc, where MacDonald told him the chocolate soufflé at Le Manoir was his second favourite pudding. Blanc pursued him as he left the restaurant to determine the first: licorice gelato. This flavour was divisive among the tasters, but elderflower and pistachio gelati followed and elicited nods and mmm’s.

The iScream owner is clearly proud of the shop’s environmental inclinations, telling us about his locally-sourced ingredients and compostable spoons. When commissioned to make pistachio ice cream with cardamom for an Indian wedding, he was unable to find ground cardamom anywhere around Oxford, until he thought to contact an Indian restaurant on the High Street that helped him out. While we sampled sorbets, we learned that many of the fruits come from Rectory Farm, and on the website he notes that they obtain fruit from Bonners, also within the Covered Market and perhaps the most ‘local’ at thirty steps away from the shop. After trying to make us guess that the spoons are made of plastic, rather than vegetable starch, he revealed that he is tracking how long they will take to compost in his backyard.

MacDonald was a keen and inviting host for this tasting event, and I know he is the same behind the counter at iScream, where he has allowed me to spend several minutes sampling and debating before arriving at my final gelato choice. His enthusiasm for the whole iScream ‘food chain’ is evident: from the grass that feeds the cows, to the eco-friendly spoons, to the final consumer tasting experience, for which he experiments to attain the creamiest sorbets and gelati. So bring on the next heat wave! You’ll find me cooling down at iScream in the Covered Market.