Wild Fermentation


The process of wild fermentation, or lacto-fermentation, relies on the invisible world of microbes that are naturally present on fruit and vegetables. Lacto-fermented vegetables are tart, tangy and sour. They are less sweet than their pickled counterparts, but this is a small price to pay for the enormous nutritional benefit they offer, and it is not too hard to get used to.

Mechanisms of Vegetable Fermentation

The exact process of lacto-fermentation is likely to be similar with most vegetables, but to date there is not much research on individual systems. The best characterized are sauerkraut and kimchi, which are sufficiently important in certain territories to have spawned industries that are willing to fund studies.

Fundamentally, vegetable fermentation occurs when LAB use carbohydrates for energy, in the process producing lactic acid, acetic acid, alcohol and carbon dioxide. This lowers the pH of the vegetables, to the point at which other bacteria cannot survive, thus preserving the food from further deterioration. Salt is added to the ferment to prevent the growth of unwanted bacteria, yeasts and fungi, especially in the early stages. LAB are salt-tolerant, so they are able to start growing quickly and triumph over these other microbes. Lacto-fermentation is an anaerobic process – it occurs in the absence of oxygen, which is achieved by excluding air from the fermentation vessel. This also prevents oxygen-loving yeasts and mould from taking hold. Find out more about utilization of natural antimicrobials in preservation.

Wild fermentation just needs naturally occurring microbes to get started. M. GILMARTIN

Wooden fermentation barrels in a rustic barn setting

Naturally Occurring Microorganisms

The soil in which vegetables are grown contains about 1010 bacteria and up to 50,000 species per gram, depending upon geographical region and terroir, before you include any equally numerous fungi, algae and protozoa. Nowadays, new advances in molecular genetics have made it easier to study these soil organisms and their role is gradually being explained, although science is so far only in the foothills of an enormous mountain. It is clear that the soil microbiota is crucial in the establishment and productivity of crops, and is the main driver of nutrient cycles, enabling nitrogen and mineral uptake by plants. The soil microbiota will also influence the microbiota of the vegetables you are fermenting; without the microbes, the fermentation cannot get started.

Microbial communities on fresh produce are affected by several factors, including natural habitat, environmental factors, produce type and cultivar, storage conditions and farming methods; plants that are grown near to the ground are more likely to have soil-type microbes than bananas, say, and cold-stored fruit and veg will probably have higher populations of cold-tolerant microbes. Many vegetables are grown hydroponically these days and may never see a grain of soil in their lifetime, however they are still able to develop microflora, albeit different from the one nature intended. Microbes exist in all parts of plants – stems, pips, cores and flesh – not just on the outside skin. Disparate parts of the same fruit or vegetable may even contain different types of microbe.

Choosing the Right Vegetables

Organic Vs Conventionally Farmed

Recent studies have shown that there are differences in the microbes on organic and conventionally farmed beetroot, apples and tomatoes. Interestingly, fewer obvious differences exist with cabbages, which seem to be variety-specific. It is not yet clear what this means in terms of the body’s gut microbiota, but it is another indication that any divergence from a more natural path will have an impact on the hidden microbiological world. The precise consequences are not yet known, but at least some of the microbes in your gut will come directly from the raw fruit and vegetables you eat.61–64

Organic beetroots and cabbages contain significantly more vitamin C than their industrially farmed counterparts, and some studies have found significant nutritional differences between these classes of vegetables65, 66, but others, not so much67. Organic vegetables will have been subjected to fewer pesticides, which is desirable in terms of soil and human health, but they are also more expensive than conventional produce, which is not something everyone can absorb. The general message is that the choice is yours; fermentation will work whether your vegetables have been produced organically or conventionally, even if people tell you otherwise.

Quality of Vegetables

Fermenting vegetables requires time and patience, so it would be a shame to ruin any ferment through poor vegetable choice. If you use the best-quality, tastiest and freshest vegetables you can get your hands on, you are much less likely to be disappointed. As vegetables age, flavours can change and a certain bitterness can develop, especially in courgettes, cucumbers and aubergines. Older cabbages also have a slightly funny taste, so the fresher the better. It is worth bearing in mind that some supermarket vegetables look fresh but might be several weeks old. Older produce is more likely to have a collection of moulds beginning to develop. Even though it is very unlikely that any mould will grow on your ferments, there is no need to challenge the system unduly.

Ideally, you should buy your vegetables from a local greengrocer who specializes in produce from small-scale farmers, where quality is of prime importance and the vegetables have not travelled too far, and have not been hanging around in a depot for weeks.

Washing Your Vegetables

Freshly soaked mulberries in water for preservation process

As already discussed in the Introduction, fermented foods, especially those made on a small scale at home, are incredibly unlikely to make you ill. The salt you add, the acid produced by the LAB, the anaerobic environment, the competition for resources with more numerous species, bacteriocins produced by the LABs: all of these factors make it very difficult for pathogens to take hold. That said, there’s no need to take chances. If you have just dug your vegetables up from the allotment, do give them a good wash, just to make sure you have removed any clumps of dirt that could harbour potentially pathogenic microbes from animal faeces in the soil.

Tasting the Vegetables

It is crucial to taste the raw vegetables before embarking on any fermentation. Anyone who has made a bitter kimchi, revolting pickled gherkins and slimy carrots, will know that it takes a while to learn from such mistakes.

If your cucumbers or lettuce are bitter before you ferment them, they will certainly be bitter afterwards – and fermented. Carrots need special attention. Some supermarket carrots are grown to be so sweet as to be almost fruit-like. The middle core is ill defined and they are full of sugar. Carrots like this will tend to stimulate the formation of dextran in your ferment, which can give a slimy texture. It is not harmful, but it is really unpleasant, so it is advisable to buy greengrocers’ carrots or organic ones. Additionally, given a choice of a bitter organic courgette and a delicious fresh-tasting conventionally farmed one, most people would choose the latter.

Frozen Vegetables

Many species of LAB will be quite happy in the freezer, so you can usually use frozen vegetables – with emphasis on the ‘usually’. To alleviate any problems, always include at least one source of fresh vegetables in the mix. For example, if you are using a bag of frozen sweetcorn, include some fresh garlic, herbs and a couple of slices of celery, to help to get things going. Alternatively, you could add some kefir whey or sauerkraut juice.

As long as your vegetables have not been irradiated (which is most unusual in the UK), there are likely to be enough microbes to start fermentation. Bacteria and yeasts grow exponentially, with one becoming 2, becoming 4, 8,16, 32, 64, and so on, so low bacterial populations in the right conditions can recover within just a few hours. Read also about advanced techniques for preserving delicate herbs and spices.

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