Frequently asked questions

A small amount of live lactic acid bacteria that turns milk into yogurt or kefir. In warm milk the bacteria feed on the milk sugar (lactose) and make lactic acid, which thickens the milk and gives it its tang. It works much like a sourdough starter does for bread.

The yogurt starter uses Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus; it sets at 42–45 °C in 7–8 hours into thick, spoonable yogurt. The kefir starter is a bacterial and yeast culture based on Lactococcus lactis; it sets at 35–40 °C in 12–14 hours into a lighter, drinkable kefir. Neither needs special equipment.

Each box holds 10 sealed 1 g sachets and one sachet sets 1 litre of milk — so up to 10 litres per box.

Lactobacillus bulgaricus was first described in 1905 by the Bulgarian doctor Stamen Grigorov, who found it in home-made Bulgarian yogurt. Our cultures are made in Bulgaria, which is where the tradition comes from.

Whole cow's milk gives the thickest, creamiest result. Pasteurised milk only needs warming; raw milk should be boiled and cooled first; UHT milk works but sets a little thinner; skimmed milk sets thin. Plant milks can ferment, but results vary a lot — full-fat oat or soy milk work best, so try a small batch first.

Yes. The cultures are meant for dairy milk and contain milk, so they are not suitable for vegans or for anyone with a milk allergy.

No. For yogurt, pour the milk and culture into a jar with a lid, wrap it in a thick blanket and leave it somewhere warm for 7–8 hours — that is the traditional Bulgarian way. A yogurt maker set to 42–43 °C for 8 hours makes it easier. Kefir needs 35–40 °C for 12–14 hours — in a yogurt maker or wrapped in a blanket.

Usually one of five things: the milk was too hot when the sachet went in (above 50 °C the culture dies — wait until 43–45 °C); the jar cooled down below about 38 °C while setting; it was moved or opened before 7–8 hours; the milk was skimmed; or the 6–7 hours in the fridge were skipped.

It fermented for longer than you like. Try 6 hours instead of 8, chill it as soon as it has set, or keep it slightly cooler (41 °C instead of 43 °C). Real Bulgarian yogurt is noticeably tangier than supermarket yogurt, so some sourness is expected.

You can, but the culture changes with every batch and the yogurt moves away from the traditional taste — the maker of our cultures advises a fresh sachet for each litre. That is why every box holds ten.

Whey. It separates naturally while the yogurt sets and cools. Stir it back in, or pour it off for a thicker yogurt.

Once the yogurt has set and chilled, tip it into a sieve lined with muslin or a clean tea towel over a bowl and leave it in the fridge for 2–4 hours. Strain it overnight and it becomes a spreadable yogurt cheese.

Up to about a week in a clean, closed container in the fridge; it gets slowly tangier. Throw it away if it smells off or shows any coloured mould.

In a dry and dark place at up to 20 °C, away from the cooker, the dishwasher and direct sun. They do not need the fridge. The best-before date and batch number are printed on the box; shelf life is 24 months from production.

No. The cultures are dry and dormant in sealed sachets and travel at normal temperatures.

Yes — light clumping comes from moisture in the air. Do not use a sachet whose foil is torn, or a powder with an unusual colour or smell; write to us with the batch number and we will replace it.

On Amazon.co.uk — the link is on every product page.

Delivery, returns and refunds for orders placed on Amazon.co.uk are handled by Amazon — please use your Amazon account. For anything about the cultures themselves, write to us; our details are on the contact page.