Proud of their traditional sour-tasting yoghurt, called simply "kiselo mlyako" or "sour milk", Bulgarians claim their country is the true home of the dairy product which is consumed all over the world.
But Bulgarian shoppers are increasingly opting for the creamier, milder-tasting yoghurts preferred by western consumers when given the choice at the dairy counter nowadays.
"Kiselo mlyako's uniqueness lies in the hot climate of the region and the very specific way in which it is prepared," said Svetlana Minkova, research director at LB Bulgaricum, a Bulgarian state-owned company that has developed around 1,000 different strains of the bacteria -- Lactobacillus bulgaricus and Streptococcus thermophilus -- used to turn milk into yoghurt.
The bacteria are isolated from plants, trees and even ants high up in the mountains, she said.
Rumen Borisov, a Bulgarian maker of bio yoghurts, likewise sees his product as "unique".
"I achieve the traditional taste of kiselo mlyako, similar to the one our grandmothers used to make, by stirring a spoonful of yoghurt into a pot of milk and leaving it wrapped up in a blanket to ferment," he says.
A Sofia-based doctor, Neycho Todorov, said he had tasted yoghurt from a dozen countries outside the Balkans and found that none of them tasted anything like the Bulgarian variety.
Nevertheless, Bulgarians who sampled yoghurt from Turkey or Serbia detected no particular difference in the taste.
"The kiselo mlyako comes under the general category of yoghurt which contains large quantities of live bacteria, Lactobacillus bulgaricus and Streptococcus thermophilus," says Emil Gotchev, head of Danone Bulgaria.
It is the particular combination of different bacteria that characterises the thickness, acidity, taste and aroma of a yoghurt, Gotchev said.
French group Danone acquired the state-run dairy company Serdika Sofia 15 years ago, a move which sparked nationalistic comments in the Bulgarian press at the time.
The company is now the biggest producer of yoghurts in Bulgaria, commanding a 35-percent share of a market estimated at some 130,000 tonnes per year.
Experts note that while Bulgarians are proud of the traditional Kiselo mlyako, they are increasingly choosing milder-tasting and creamier varieties.
Gotchev said that while Danone was careful to cultivate the traditional Bulgarian kind, "we're opening customers up to a whole new range of products -- yoghurt with fruit, fresh milk drinks, probiotic products."
Gotchev poo-poohs the myth that the famous Lactobacillus bulgaricus bacteria is only found in Bulgaria.
It was simply named after the home country of its discoverer, Stamen Grigorov, who was the first to isolate and describe the bacteria that causes the milk to ferment, he said.
In 1905, Grigorov, of whom most modern-day Bulgarians have never heard, took a sample of milk curd from his home country to Geneva for scientific examination.
His granddaughter, Julia Grigorova, told AFP that, at the time, a study by the Institut Pasteur in Paris had shown that the highest concentration of people aged over 100 in Europe was in the Rhodope mountains in southern Bulgaria. And their daily diet consisted predominantly of kiselo mlyako.
"This explains the interest in the product back then," Grigorova said.
In the early 20th century, Russian microbiologist Ilya Mechnikov, a Nobel Prize laureate in Physiology and Medicine, similarly suggested that ageing is caused by toxic bacteria in the gut and that Lactobacillus bulgaricus can counter that.
He drank sour milk every day.
Other Bulgarian and Japanese researchers have found that yoghurt strengthens the immune system and helps prevents tumour growth. Its high concentration of calcium also helps against osteoporosis and reduces cholesterol levels.
The beneficial health effects of Bulgarian yoghurt have made it particularly popular in Japan where millions of people start their day with a cup of yoghurt. LB Bulgaricum has been present in Japan since 1972.