The origins and history of fermentation
From untimely “immediate need” to “carefully sought” result, from “spontaneous” process to “knowingly managed” method: fermentation has developed over the course of time. Italy is no exception: there are numerous products and preparations which, from the Alps to Sicily, are based on application of this process.
They include sauerkraut and brovada (turnips left to soak in marc) in the north-east and formaggio di fossa (cheese left to ripen in underground cellars) in the Tuscan-Umbrian-Emilian Apennines. Without forgetting conciato romano cheese from the province of Caserta, Cetara anchovy sauce and the strong ricotta cheese of the Apulia region.
Fermented foods can be preserved for a longer time and this was extremely important for rural civilisations, for which the urgent need to overcome the limitations posed by the seasonal nature of foods and the lack of efficient food preservation systems were ever-present concerns.
Thus the success of this system of production and preservation, considered to be an innovative and eccentric habit of Northern European culinary traditions, also has its roots in the gastronomic culture of the Mediterranean area.
Making fermented foods at home
Fermented foods are easier to make than you would imagine. The bacteria and yeasts that form during fermentation make the foods healthier and less prone to attack by competing bacteria, which can sometimes be harmful to human health.
The transformation produced by the fermentation process is also beneficial to intestinal health and is of importance for the nutritional and sensory aspects of the product itself and its preservation. The activity of the microorganisms makes the food more digestible (consider yoghurt and kefir, for example), increases the amounts of vitamins and minerals available, produces the aromatic molecules that are responsible for the changes in colour, consistency and fragrances of the products and helps them to keep for a longer period of time.
This is why certain fermented foods are known as “probiotic”, thanks to their high content of live microorganisms that contribute towards the health of intestinal microflora.
What is fermentation?
Fermentation is a chemical-physical transformation of food by microorganisms, namely bacteria, yeasts or moulds. In scientific terms, fermentation is a process through which microorganisms convert sugars into another metabolite, in the absence of oxygen.
PFermentation can only be achieved by creating a selective environment that is hospitable only to the desired microorganisms. The key players in the fermentation process are lactobacilli, assisted by acetic bacteria or by yeasts.
Raw foods, especially vegetables, are full of these microorganisms and are thus ideal for delicious home-made preserves. Unlike pickled preserves, in which the acidic fragrance of the vinegar tends to predominate, fermented vegetables become more acidic while still retaining their neutral aroma. Lactic acid is, in fact, less pungent. The vegetables remain crunchy and juicy.
Common kitchen utensils are all that is needed for perfect fermentation: chopping boards, knives, a mandoline slicer, wooden spoons or pestles and glass jars with a hermetic seal. Glass is inert and transparent, making it the best option, as it also allows the fermentation process to be visually inspected. Various solutions can be adopted to ensure the food remains fully submerged under brine, such as plastic mesh discs, glass or ceramic weights or bags (with no writing on them!) of drinking water. Everything must be food-grade.
A gas (mainly carbon dioxide) is produced during fermentation. For the process to proceed correctly, off-gassing is required by opening the jar lids twice a day during the first few days until the gas is no longer produced. The gases released during the production of fermented vegetables do not create high pressures.
In contrast, fermented beverages or fruit, which have a high sugar content, give off high quantities of CO2 during the production process and failure to off-gas could cause the jars to explode.
The utensils and work surfaces must be clean. The jars must be washed and dried. They can be sprayed with 95% ethyl alcohol diluted in water (70% alcohol and 30% water).
There is no need to boil jars used for fermentation: proliferation of the pathogenic bacteria that remain in the containers is inhibited by the products of fermentation. The vegetables or other foods used must be washed under running water without the use of products (such as sodium bicarbonate) that could weaken the good bacteria they contain.
Foods that can be fermented
Any fresh food in excellent conditions can be fermented. It is advisable to start with vegetables, which can all be fermented, including flowers and pulses. They are naturally rich in good bacteria and are also less likely to be contaminated by the pathogenic sort. Owing to the proliferation of undesired bacteria, unpleasant odours or flavours could form if the foods are old or poorly conserved.
The following parameters can be altered to create selective environments:
pH (potential hydrogen) is important for safe fermentation as it influences the growth of bacteria in the fermented foods. pH measures the acidity or basicity of a product on a scale of values from 0 to 14: the lower the value, the higher acidity will be.
The pH value in fermented products is linked to the amount of salt in the product itself and its value must be no higher than 4.3 in relation to 2% of salt. The sensitivity of bacteria to salt creates a selective environment that favours lactic bacteria, which withstand and feed on the brine, thereby controlling the stability of the pH and fostering the development of the fermentation aromas. pH can be checked by using litmus paper, which can be purchased at a pharmacy, or by using more specific instruments, such as a pH meter.
Sodium chloride (kitchen salt) creates the ideal conditions for certain lactobacilli and yeasts and is inhospitable for undesired microorganisms. Non-iodised salt is best, as it is low in the iodine that could inhibit the positive bacterial flora. At least 2% of salt must always be used in order to avoid the proliferation of undesired microorganisms. It is essential to follow specific recipes word-for-word when preparing fermented products.
Salting can be:
1) “dry”, by adding salt to the foods so that they produce sufficient liquid to remain submerged. The quantity of salt must not exceed 20% of the weight of the vegetables used (e.g. capers);
2) obtained by using brine, which is a solution of salt and water. Unchlorinated water is required in this case, as chlorine is a powerful bactericide. This can be achieved either by filtering the water through a carbon filter or by boiling it and then leaving it to cool. The quantity of salt must never exceed 10% of the weight of the water (e.g. olives). If the vegetables are bitter, throw away the water produced after adding the salt or change the brine every day to dilute the bitterness.
In order to maintain the right amount of salt in lactic fermentation, it is important to ensure that oxygen is only present in a small quantity or entirely absent. When brine is used, the foods are submerged in it, whereas, if the dry salting method is employed, it is necessary to consider the quantity of water in the food, which must always remain submerged in its own liquids. If higher amounts of oxygen are present, the percentages of salt must be increased.
Temperature has a major influence on fermentation as it helps certain bacterial strains over others. In lactic fermentation of vegetables, the bacteria prefer temperatures between 4 and 28°C. In the production of yoghurt, they function at around 40°C. Room temperature is suitable for making fermented products at home. If the temperature exceeds 30°C, it is preferable to complete the fermentation process by transferring the jars to the refrigerator to prevent the vegetables from becoming soft.
Ultraviolet rays alter certain molecules present in food and trigger oxidative processes. It is advisable to keep the jars away from direct light sources.
The sugar in foods is usually sufficient to ensure that fermentation occurs. Sugar can be added to assist the proliferation of bacteria or to obtain a different degree of acidity and therefore different results.
This leads to an increase in the production of gases during the initial days of fermentation, especially in certain types of fermented products, such as beverages. It is important to remember to release the gas from the containers at least once a day and to use containers able to withstand high pressure, to prevent them from exploding.
How long does fermentation take?
The time required to ferment foods varies considerably and depends on the temperature and amount of salt. It is difficult give precise indications about production times unless temperature control instruments are used, such as a yoghurt maker or a proving cabinet. It is, however, possible to establish when fermented products are ready, i.e. when the production of gas has stopped or slowed down.
The best way to be certain is to measure the pH. At the beginning, it is advisable to follow the recipes carefully, as all the steps and times for safe and successful fermentation are explained. The fermentation process can be slowed down simply by placing the sealed jars in the refrigerator. This will preserve the foods they contain for months.
What is lactic fermentation?
Lactic fermentation is a type of fermentation performed mainly by lactic acid bacteria (LAB) or lactobacilli. This type of fermentation takes place both in milk-based fermented products and fermented vegetables and it is unlikely to occur if large quantities of salt or sugar are present. Lactic acid is not the only compound produced during the transformation of foods. There is also a group of secondary products that give the ingredients a pungent and aromatic flavour and a good level of acidity.
The bacteria in lactic fermentations are divided into two groups with different metabolisms:
- Homofermentative, which produce almost exclusively lactic acid from the sugars present
- Heterofermentative, which, from the sugars present, produce 50% lactic acid and 50% ethanol, acetic acid, citric acid and carbon dioxide.
When fermentation begins, the heterofermentative LAB are the ones that lead the way and fermentation releases a large amount of gas. Fermentation is less visible when homofermentative LAB are mainly present.
Yeasts are members of the fungus kingdom and have an anaerobic metabolism, just like LAB: they obtain energy from sugars to produce ethyl alcohol, CO2 and aromatic esters. Depending on the food to be fermented, yeasts may be more or less active in helping lactobacilli in the lactic fermentation of vegetables. This applies especially to foods with a higher sugar content, such as vegetables from the Brassica genus, fruit or starchy tubers.
A seconda dell’alimento che si va a fermentare i lieviti possono essere più o meno attivi ad aiutare i lattobacilli nelle fermentazioni lattiche dei vegetali. Questo vale soprattutto per i gli alimenti più ricchi di zuccheri come le brassicacee, la frutta o tuberi amidacei.
Starter or stock bacterial cultures
Some bacterial cultures can be purchased online (such as milk kefir grains or a kombucha stock culture). Starter cultures selected in a laboratory with specific bacteria strains that provide constant fermentation results (such as yoghurt) can also be used. Starters can be purchased from pharmacies or online. In other cases, the bacteria naturally present in foods can be used.
Possible problems and solutions
Different types of moulds exist, some of which are noble and wholesome, while others are toxic. Unfortunately, it is hard to distinguish between them. If moulds develop in fermented products, it is therefore better to throw everything away.
The odour of fermentation attracts a lot of fruit flies. It is essential to close the jars tightly with their lids or, in the case of certain types of fermentation, with a piece of gauze or linen cloth secured with an elastic band. If flies get into the jar and lay eggs, the product must be thrown away.
When the fermentation process is lengthy and only a small amount of salt has been used, the brine could thicken and the food inside become soft and not very pleasant. The product must be thrown away in this case as well.
It is perfectly normal for the brine to become cloudy sometimes. This is not a problem and it can even be used as a starter for other fermented products.
Sediments on the bottom of the jar
These are also perfectly normal, especially when the brine is cloudy and the particles settle on the bottom over time.
Pinkish hue on the vegetables or on the sides of the jar
If the vegetables are not completely submerged under brine, bacteria could develop and cause intestinal problems. Here again, the fermented product should be thrown away.
The fermented products lose their colour
The colour of the vegetables could fade during fermentation, but this is perfectly normal. Fermentation processes, including acidification, are the cause of these changes, which may be more or less evident.
How to store fermented products
Fermented products made with less than 2% of salt (e.g. sauerkraut) can be kept in the refrigerator for up to around six months. Those with 2% of salt or more can be kept at room temperature for several months.
The higher the amount of salt, the longer the storage period. It can be lengthened still further by keeping the products in the refrigerator. Products containing a very high quantity of salt (20% and above) can be kept at room temperature for over a year.
Fermentation: choose the right jar
jars are suitable for fermentation. Choice of the jar size depends on the quantity of product you want to make. Several parameters must always be considered regardless of the type of jar used and the quantity of product being fermented:
- pH value:
this is important for the safety of the preparation. It allows you to check the acidity of the product, which must not exceed the value of 4.3 in relation to 2% of salt.
sodium chloride, in certain percentages, creates both ideal conditions for the proliferation of the microorganisms required for the process and inhospitable conditions for pathogenic microorganisms.
monitoring: a high concentration of carbon dioxide is produced during fermentation. Off-gassing the jars is important to prevent them from exploding.
the jars must be kept in a cool, dry place away from direct light sources.
Lock Eat jars are suitable for fermenting vegetables, kefir and spicy sauces. During the off-gassing phase, the brine could splash onto the external metal wire of the lid and cause it to oxidise. This does not jeopardise or influence the result of the final product, as the metal wire does not come into direct contact with the fermented product.
Large capacity, wide-mouthed Handy jars are ideal for fermenting vegetables, while Food jars are suitable for spicy sauces and the jugs are great for kefir.
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