Let’s make Kefir

When a batch looks wrong

Start with the
symptom.

Kefir changes with temperature, ingredients and time. Find what you’re seeing, then work through the smallest useful correction.

When to throw it away

Fuzzy or coloured mould, a rotten or putrid smell, or a damaged pressure bottle are not recovery projects. Do not taste the batch. Discard it, clean the equipment and begin again.

18 answers

milk kefir · brewingMy milk kefir is thin

Thin kefir can still be properly fermented. New, recently chilled or stressed grains often need several consistent batches to regain strength; milk choice and a cool room also affect texture.

What to do

  1. Keep the jar around 20–24°C and out of direct sun.
  2. Use a little less milk for the next few batches.
  3. Feed with fresh dairy milk every 24 hours until activity is reliable.
milk kefir · brewingMy milk kefir separated into curds and whey

Separation usually means the batch fermented too far, not that it failed. Warm rooms, too many grains or too much time accelerate separation.

What to do

  1. Stir gently and strain the grains.
  2. Shorten the next ferment or use more milk.
  3. Refrigerate the finished kefir promptly.
milk kefir · brewingMy milk kefir is too sour

Acidity continues to rise while kefir ferments. A warmer room, longer ferment or high grain-to-milk ratio will make it sharper.

What to do

  1. Strain earlier next time.
  2. Increase the amount of milk without increasing grains.
  3. Blend the current batch with fruit or use it in cooking if it smells clean.
Milk & water · grainsMy grains are not doing anything

Shipped, dried or refrigerated grains can be dormant rather than dead. Look for any souring, thickening, cloudiness or reduction in sweetness across several fresh feeds.

What to do

  1. Use the standard unflavoured milk or sugar-water recipe.
  2. Refresh every 24 hours for milk or 24–48 hours for water.
  3. Keep conditions steady for several consecutive batches before judging them.

Safety firstDiscard grains that show fuzzy mould or a rotten, putrid smell.

Milk & water · grainsMy grains are not growing

Growth rate varies and is not the best measure of health. Grains that reliably ferment a batch may be healthy even when their volume changes slowly.

What to do

  1. Judge activity by taste, aroma and fermentation time.
  2. Avoid repeated recipe, temperature and ingredient changes.
  3. For water kefir, use dechlorinated water and a balanced mineral supply.
water kefir · brewingMy water kefir is still very sweet

The grains may need more time, a warmer position or a smaller batch. The first ferment should taste noticeably less sweet than the starting sugar water.

What to do

  1. Allow up to 48 hours in a cooler room.
  2. Check that the water is dechlorinated and the sugar fully dissolved.
  3. Run two or three plain recovery batches without fruit or juice.
water kefir · flavouringMy water kefir is flat

The open first ferment is often only lightly bubbly. Most obvious carbonation develops after strained kefir is sealed for a second ferment.

What to do

  1. Use a sound pressure-safe bottle with a reliable seal.
  2. Add a modest amount of fruit or juice after removing the grains.
  3. Leave at room temperature briefly, then chill completely before opening.
water kefir · flavouringMy bottle is too fizzy or gushes

Fruit sugar, warmth and time can build pressure quickly. A gushing bottle is over-carbonated and must be handled cautiously.

What to do

  1. Refrigerate the bottle thoroughly before touching the closure.
  2. Open very slowly outdoors or over a sink, pointed away from faces.
  3. Use less fruit or a shorter second ferment next time.

Safety firstNever use decorative glass or a damaged bottle for sealed fermentation.

Milk & water · brewingMy kefir smells yeasty

A light fresh-bread or beer-like aroma can be normal. A harsh rotten, sewage-like or putrid smell is not.

What to do

  1. Compare the aroma with a clean sour or fresh-yeast smell.
  2. Refresh the grains in a plain, correctly measured batch.
  3. Clean the jar and utensils before the next cycle.

Safety firstWhen the smell is rotten or you are uncertain about contamination, discard the batch.

Milk & water · brewingThere is a film or fuzzy growth on top

A thin smooth yeast film can sometimes form, but fuzzy, raised or coloured growth should be treated as mould. It is not safe to scrape mould off a liquid ferment.

What to do

  1. Do not taste the batch.
  2. Discard the liquid and grains.
  3. Wash and sanitise the equipment before starting with new grains.

Safety firstFuzzy green, blue, black, pink or white growth means discard everything.

water kefir · grainsMy water kefir grains are brown

Colour often comes from the sugar used. Brown, raw or mineral-rich sugars can tint otherwise healthy grains.

What to do

  1. Check that the grains still ferment normally.
  2. Return to a lighter cane sugar if you want to confirm the colour source.
  3. Act only if colour comes with disintegration, mould or an off smell.
water kefir · flavouringMy water kefir tastes bitter

Citrus pith and peel become bitter when left too long. Strong herbs and spices can do the same.

What to do

  1. Use juice or thin zest without the white pith.
  2. Shorten the infusion or second ferment.
  3. Remove herbs and spices before refrigeration.
milk kefir · flavouringFruit made my milk kefir curdle

Acidic fruit can make milk proteins tighten or separate. It is usually a texture issue when the kefir and fruit were both fresh and the drink was prepared cleanly.

What to do

  1. Blend fruit into cold finished kefir just before serving.
  2. Use zest rather than juice for a citrus-infused second ferment.
  3. Keep flavoured milk kefir refrigerated and use it promptly.
milk kefir · storageHow do I pause milk kefir grains?

For a short break, cover the grains generously with fresh milk and refrigerate. Cold slows them but does not stop fermentation completely.

What to do

  1. Use a clean lidded jar with enough fresh milk.
  2. For a longer break, refresh the milk periodically.
  3. Expect one or more room-temperature feeds to restore normal speed.
water kefir · storageHow do I pause water kefir grains?

Refrigerate the grains in fresh sugar water for a short break. They may be sluggish when restarted.

What to do

  1. Use dechlorinated water and the normal sugar ratio.
  2. Keep the grains submerged in a clean lidded jar.
  3. Discard the storage liquid and run fresh room-temperature batches to reactivate.
Milk & water · storageHow should I store finished kefir?

Strain out the grains, refrigerate the finished drink in a clean container and remember that it continues to ferment slowly in the cold.

What to do

  1. Label the container with the date and flavour.
  2. Keep flavoured kefir cold.
  3. Open carbonated water kefir slowly and use sensory judgment before drinking.
Milk & water · brewingCan I use metal utensils?

Brief contact with clean stainless steel is generally fine. Avoid reactive, rusty or damaged metals and do not store kefir in them.

What to do

  1. Use stainless-steel, food-safe plastic, glass or silicone tools.
  2. Replace rusty strainers or damaged lids.
  3. Use glass for fermentation and storage.
Milk & water · grainsCan I switch milk, water or sugar?

Live grains adapt best when changes are gradual. Abrupt changes can temporarily alter speed, flavour and grain growth.

What to do

  1. Change one variable at a time.
  2. Give the grains several batches before evaluating the result.
  3. Do not swap milk grains and water grains; they are different cultures.