"We've been amazed at how many people genuinely care about that. And of course, there are the people that want the fat-free element. We are a healthy indulgence."
What's more, the women are profiting from its celebrity endorsement, as Mrs Gestetner admits "this gives it a cool edge. Loads of famous people are photographed with frozen yoghurts, which gives it a funky fashionable element." Indeed, yoomoo has a strong celebrity following. Actress Amanda Holden "is a regular" and John Terry is "completely hooked". He particularly likes the chocolate yoomoo. Television presenters Fearne Cotton, Holly Willoughby and comedian Michael McIntyre are also fans.
The idea for yoomoo was born in 2009. Mrs Gestetner, who has a background in marketing, PR and branding and had worked at Condé Nast, was visiting Los Angles when she witnessed the popularity of frozen yoghurt first hand. "There was a massive frozen yoghurt lifestyle out there and I thought: how about doing that here."
Arranging an initial business meeting in Starbucks, she recruited her close friend Mrs Pyser, who was running a private catering company specialising in ice cream at the time. The next step was to secure investment. "The first few months consisted of a lot of meetings and business plans," says Mrs Gestetner, a member of London's Marble Arch Synagogue. "As mums with six children between us, we faced a massive challenge trying to convince the men in grey suits that we had what it takes and were serious about it." Determined and passionate, the women have raised "a seven-figure amount" and contacted Harrods with their concept.
"We aimed high from the start. We approached them and did our presentation." Six months later and their products were in stock. Half a dozen stores in as many months followed; in London, Kent, Cardiff, Leeds, Milton Keynes, Manchester, and more recently, Canary Wharf - the UK's first self-service yoghurt bar. Prices range from £2.30 to £5.60, plus there are pay-as-you-weigh options.
With 70 staff, yoomoo sells around 7,500 frozen yoghurts a week and numbers are growing rapidly. The mums cite "dedication, bloody hard work and a sense of humour" as key to their success.
But is the frozen yoghurt trend just a fad, following the success of smoothies, juice bars and cupcakes? "No way," says Mrs Pyser, who lives in Mill Hill, north London. "We don't think so at all as there is such a focus towards healthy eating and healthy lifestyles today.
"We don't think the trend is going anywhere. We think it's growing not diminishing." Besides, says Mrs Gestetner, consumers are buying into the frozen-yoghurt lifestyle. "People build it into their daily routine. There are fruity toppings for the gym-goers and health conscious, and there are 'naughty' toppings for those who want a sweet fix but don't want to go and gorge on a Mars Bar.
"A frozen yoghurt is something you can have at any time and without feeling guilty. They are also popular with children, who have become slightly more health conscience and aware of what they are eating."
Hardly surprising then that new outlets are popping up on the high streets on a regular basis. But the duo are not concerned about market saturation. "The more that open the better as that increases market awareness. It's great that they are there. We are not competing for the same spot."
Pressed for other opportunities in the food industry, they acknowledge that convenience and lifestyle are paramount considerations. "Life is fast" says Mrs Gestetner. "The healthy takeaway fast-food options are good. And you need something that appeals to everybody and not just aiming at one age group."
