Lacto-fermentation: Getting Started


Preventing Potential Problems

Lacto-fermentation can be as simple or as hi-tech as you like, but the principle remains the same: when fermenting vegetables, it is important to provide an anaerobic environment for your microbes, as these conditions allow LAB to thrive, and produce lactic acid and carbon dioxide. You must also consider how that gas is going to escape. An anaerobic environment will prevent two potential problems: contamination and oxidization.

Yes, the process needs the microbes, but not this many! Give vegetables a thorough wash. ADOBE

Contamination is possible because the starting vegetables are not just covered with bacteria, they may also harbour mould spores and yeasts. Mould spores travel through the air all the time – witness an unattended fruit bowl to see the potential for decomposition – and most moulds thrive in an oxygen-rich environment. Keeping air out of the vessel will minimize the risk of mould growth.

Oxidation is another potential problem with a poorly sealed fermentation vessel, or a vessel that has been repeatedly opened to release pressure or to taste the contents. The contents in the top two or three centimetres will have a duller, less appealing colour than the rest of the jar. When the microbes are exposed to oxygen, some of them are able to use this to generate energy, but they do not make lactic acid this way. Instead, many different pathways are activated, forming products that do not enhance either the flavour or the appearance of fermented foods.

The vessel you choose for your ferment depends to some extent upon the type of ferment you are making. If you open the jar, you will disrupt the environment that you have tried so hard to create, so it is important to consider this. The longer the fermentation time, the greater the chance of contamination and/or oxidation occurring, especially if you keep opening the jar. Sometimes, fermentation can proceed more rapidly in a Kilner jar if it is not vented. This is because the carbon dioxide is not able to escape, and can become dissolved in the fermenting mixture, as carbonic acid, thus lowering the pH even further. This can influence the growth of certain types of LAB. It is not usually a problem – it actually seems to help kimchi!

  • Suitable Vessels
  • Fermentation Crock

If you decide to go ‘old school’ and use a ceramic crock, you must find one that is designed specifically for the purpose, as some ceramics can contain lead. They use a water seal to prevent mould contamination. The porosity is said to improve the quality of the fermentation.

Different vessel options: jam jar and lid, plastic kimchi box, ziplock bag, mason jar with twopart lid, cliptop jar, lidless jar and bag of brine, wooden barrel, ceramic crock and Sterilock jars.

  • Pros: usually capacious; unlikely to explode; attractive addition to kitchen, exciting when it is time to open up!
  • Cons: hard to see what is going on inside; expensive; channel must be kept full of water to maintain seal.

Wooden Barrel

This traditional vessel is not commonly used in the UK, but may impart an additional layer of flavour, rather like ageing wine.

  • Pros: flavour enhancement; natural material; porous; good for large quantities.
  • Cons: hard to clean; expensive; not see-through.

Kilner or Other Clip-Top Jar

Kilner jars and other clip-top vessels are very popular for fermenting, especially in the UK, despite their limitations. Make sure they are designed for culinary purposes and not ‘gift-type’ jars, which may not be sturdy enough. Replacing the clip with a rubber band wound around a few times, giving slightly more expansion than a metal clip, can avoid the need to vent. They are best for short ferments, and not ideal for long ferments.

  • Pros: cheap; available; transparent; ideal for small quantities; easy to clean; does not retain odours; replaceable gaskets.
  • Cons: breakable – glass is a liability and must be checked for weaknesses; could crack under pressure, although gaskets usually prevent this.

Plastic Box

Vented food-safe plastic boxes are now available for fermenting.

  • Pros: safe; easy to clean; come in all sorts of shapes and sizes.
  • Cons: do not allow view of what is going on inside; cannot use full capacity as lots of room is needed for generation of carbon dioxide; the smell of the plastic is rather unappealing, although it does not transfer to the food. Get informed about what you should and should not dehydrate.

Mason Jar With Screw-on Two-part Lid

These are a popular choice for fermenting in the USA, although the quality of the metal lid is not always the best.

  • Pros: cheap; easy to find; easy to wash.
  • Cons: rust can form on the lid, which could taint the ferment; the lids are not really suitable for venting – they are really for canning.

Vented Fermentation Jar

Pouring passion fruit juice into jar with ice for preservation

Can be used with a standard mason jar, with a valve mechanism that will let carbon dioxide out of the jar without letting oxygen back in. Easy-to-use valves with membranes are available these days, although you can also use a traditional glass tube set-up if you prefer, or if you already have one.

  • Pros: removes the need to vent; can be extremely reliable (depending on manufacturer); membrane versions easy to clean; one-time purchase; look efficient.
  • Cons: high cost; can get blocked with mashed-up ferments.

Large Glass Jar With Lid

For no-frills fermenting, and short ferments only.

  • Pros: inexpensive; economical; reusable; recyclable.
  • Cons: no mechanism for release of carbon dioxide, so must be vented, with risk of oxidation/ contamination; may not have shoulders for easy submersion of brine; lids can rust and harbour contaminants.

Large Glass Jar with Plastic Bag-of-Brine Stopper This is great for no-frills fermenting. Filling the bag with brine means that, if there is a leak, the salt concentration in the ferment will not be diluted.

  • Pros: inexpensive and easily available; safe; see-through, no venting required; suitable for long or short ferments; reusable.
  • Cons: bag can burst; uses plastic.

Ziplock or Vacuum Seal Bags

The bags need to be sturdy with a good seal, and made of a high-quality material. Ziplock bags can be reused until the seal fails.

  • Pros: inexpensive and easily available; safe; see-through; suitable for long or short ferments.
  • Cons: may need venting; plastic can make ‘sweaty’ flavours long-term.

Submerging the Vegetables

When fermenting vegetables (with the exception of short, paste-based kimchi and piccalilli ferments), it is important to ensure that they are completely out of contact with the air and in contact with the salt-containing brine – at all times. If portions of your vegetables stick up above the level of the brine, they will be more susceptible to the effects of oxidation and discolouration, and could provide a tasty source of carbohydrate for mould growth, if any oxygen is present. There are various ways of achieving this submerging, dependent to some extent upon the type of vessel you are using.

Options for submerging the vegetables: repurposed food-safe plastic discs; shot glass; bag of brine and rubber band; stone or glass disc; or the top of a cabbage. Get informed about dehydrating methods.

Re-Purposed Food-Safe Plastic Disc

This works well for a mason jar, or any vessel with shoulders. You can easily recycle any piece of food-safe plastic for the task. Cut a circle from a lid or tub that is about 1cm larger than the mouth of the jar. Ease it into the jar and position it so that it sits on top of the vegetables, held in place by the shoulders. In some countries, it is possible to buy special inserts called ‘pickle pushers’, but these do not seem to be readily available in the UK yet.

Glass Weight

Be sure to use a weight that is designed for the purpose, as some decorative glass contains lead. They are quite expensive but very effective – perhaps something for your Christmas list.

Vegetable Pieces

Person slicing vegetables for pickling in glass jars on table

If you are fermenting a cabbage, you can use the end to keep the rest of it under the brine. You could also use carrot sticks that are longer than the jar opening, or anything else that springs to mind. Ensure that this is also included in your brining.

Small Glass Jar or Shot Glass

These can work well in a jar that does not have shoulders and for tightly packed vegetables. Place the glass on top of the vegetables to bridge the gap to the lid. When the lid is shut, the jar or glass will press down on the vegetables underneath and keeps them below the brine.

Plastic Bag Filled With Brine

Fill a bag with 2% brine and secure it with a rubber band. The water needs to be brined in case the bag bursts. If it just had plain water in it, it could reduce the salt concentration in the vessel to potentially unsafe levels. If you have a jar without a lid, a bag filled in this way can be used as both a lid and a weight. Ensure that the bag is in complete contact with the top of the vegetables.

A Stone

A stone can be effective for well-packed vegetable ferments, but not for whole vegetables, as it will simply fall to the bottom! Certain types of stone should be avoided, as they may contain elements that could leach into the ferment under the acidic conditions. Do not use limestone because the calcium carbonate will react with the lactic and acetic acid in your ferment and dissolve. If you are using a stone from the garden, sterilize it first by soaking it in Milton fluid according to the instructions and then rinsing thoroughly. Alternatively, you could put it inside a plastic bag.


Some people do not agree with the practice of submerging. If you have a casual approach to contamination and discolouration, or if you are just doing a short ferment, feel free to ignore the instructions. It is certainly less important in the vented jars, where an oxygen-free environment is easy to create, or with a short sauce-covered ferment. However, in the case of a Sterilock jar, for example, it is important to submerge the cabbage for a different reason: if it rises in the jar as a result of carbon dioxide production, bits of cabbage could get stuck in the valve and stop it from releasing excess gas.

Using a Starter Culture

As long as you are using fresh vegetables, there is no need to use a starter culture for vegetable fermentation. Recipes suggesting the addition of whey, starter culture sachets or backslopping from previous batches to ‘get things going’ are missing the point – it will ‘get going’ all by itself within 24 hours. There is one exception: when you are fermenting cooked vegetables, such as chickpeas.

Using up Odds and Ends

People usually ferment things in quite large quantities – this has arisen traditionally, because if you didn’t ferment it you couldn’t store it, and also because if you’ve to wait three weeks for your sauerkraut, you might as well make a big batch. But it doesn’t have to be that way – odds and ends of (fresh) vegetables can easily be chopped and brined in small jars – cauliflower leaves and stems for example that would otherwise just go into the compost, can make a delicious one-serving ferment.

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