Process to preserve - Principle of vegetable preservation

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Process to preserve - Principle of vegetable preservation 2

Objective: to obtain stable, healthy and wholesome products.

In this sense we seek to control the development of microorganisms


Microorganisms are living things that need conditions that are available to them.

favorable to live: they need nutrients (provided by our vegetables),

water, heat, oxygen and neutral ph.

To preserve our vegetables we can therefore influence 4 factors to limit or

inhibit their proliferation:

- Water (mainly "free water", AW)

- The ph (acidity)

- The temperature (go well below or above the main zone of

development of microorganisms between 10 and 65 ° C)

- Oxygen: create anaerobiosis.

COLD: Freezing and deep freezing.

The cold stops or slows down cell activity, enzymatic reactions and

development of microorganisms. It thus extends the shelf life of food

food by limiting their deterioration. This is not a destruction of micro-

organizations but from a shutdown of their activity, it resumes as soon as the

temperature conditions are favorable again.

By taking young vegetables after harvest, these processes have the advantage of stabilizing

the product without loss of nutrients (compared to a fresh vegetable lying around in the fridge,

in transport or in store): the water-soluble vitamins remain.

These two processes are a method of cold preservation at a temperature of -

18 ° C. Their difference lies in the means of achieving it, which has an impact on the

structure of crystallized water.

Freezing is the domestic means of cold preservation. The descent in

product temperature to reach -18 ° C is relatively slow: around 24

hours. Water takes its solid form by consisting of large crystals. Large crystals

of ice breaks the structure of plant cells, which is why vegetables

thawed tend to be soft, watery.

The final quality of frozen products depends on:

- The initial quality of the vegetables (freshness, healthy product, etc.)

- Freezing and storage technique (so that the product reaches the

faster than the expected temperature, avoid large, dense packages and favor

trays with your vegetables arranged in thin layers)

- Thawing conditions (do not thaw at room temperature, which may

allows bacteriological proliferation to resume its cruising speed. To choose

rapid thawing by heating, which kills germs as they

wake up, or place your product at 4 ° C in the refrigerator)

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To maintain the quality of the flavors, consumption must take place in the months to

come: the "taste of freezing" does not come from freezing itself, but from the fact

that we mix the products in the freezer and that the sealing of the

freezing to transfer aromas only lasts a few days. There are bags

waterproof to aromatic transfers lasting 9 months, use this type of bag.

Deep-freezing corresponds to the industrial means of cold preservation:

products are exposed to a temperature between -30 and - 50 ° C in order to achieve less

one hour at a core temperature of -18 ° C. Here the water contained in the cells is

finely crystallized. These finer crystals damage the product less: the fibers do not

are not broken, which preserves flavor and nutritional qualities.


Salt is an ancestral technique for preserving food, mainly

meat and fish.

Salt removes water from the product, it decreases the activity of the free water contained in the product,

this process slows down or stops microbial development.

There are two techniques: salting (or curing) and brining,

Salting or curing: The salt is spread directly on the surface of the food (salting with

dry). This technique is mainly effective for cheeses, meats (cold cuts)

and fish (herring, salmon, etc.); for vegetables it is little used because it requires

salt strongly (25 to 30% of the weight of the product) and therefore desalt (rinse) abundantly

before consumption.

This process is more interesting by taking it backwards, with the idea of ​​creating condiments:

salts flavored with aromatic plants (basil, parsley, etc.) or cut vegetables

very finely (celery, fennel, carrots, leek ...)


It is a salt water preparation in which the vegetable is immersed.

The brine works by osmosis, that is to say that part of the salt migrates into the food and that the

salt concentration in the food equilibrates with that of the brine.

Brine is always used cold.

Salt water will promote the proliferation of lactic bacteria, this process is lacto

fermentation (see document on fermentations).

Salt brine can have another function: for example for olives, it is

remove the bitterness and prepare the conservation, the brine is renewed several times

for 15 days, then the olives are preserved in oil.

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Oil canning has been practiced since Antiquity.

Olive oil is most commonly used for preserving vegetables, but it is

possible to turn to sunflower oil, rapeseed ...

The choice of a quality oil is crucial, choose an extra virgin olive oil, if possible

of first cold pressing whose extraction by simple mechanical pressing preserves

nutritional interest and initially promotes the conservation of the oil.

Vegetables (sun-dried tomatoes, candied garlic, blanched artichoke hearts, small peppers

red goat cheese ...) are covered with oil, then you press to chase

the remaining air and promote the hermeticity of the preparation, this fatty substance protects them from

new air entry and prevents microorganisms from breathing and growing.

Spices, aromatics and condiments are welcome to enhance your preparation.

The jar is sealed and kept cool for a month or two, because

the oil does not eliminate the water (hence we can favor previously dried vegetables or

bleached - decrease in free water), nor microorganisms.


The limit between acid and basic for water is 7. For a food product

this limit is 4.5. A product which has a Ph equal to or less than 4.5, does not need

heat treatment to optimize its conservation. There is a device for

measuring the ph is the phmeter (between 70 and 150 euros). The pH is measured on the product


At harvest the vegetables have different ph values, very few are acidic (aubergine

between 4 and 5, asparagus between 4.5 and 6, courgette between 4.70 and 5.70, sorrel between 3.5 and 4.10,

tomato between 4 and 5), all other vegetables are over 5.

In tomatoes, the acid varieties are Romas, Andines and sometimes Coeur de

beef. They are useful for acidifying preparations (e.g. in ratatouille the

tomato and eggplant pair support the acidification of the product, but are not

sufficient), heat treatment should be added.

The ph value makes it possible to choose the appropriate conservation treatment.

Acidification is obtained by several processes.

By adding vinegar, vinegar by acidifying the medium blocks the development

bacteriological. It is often coupled with sugar in order to correct the acidity at the level


These are the recipes for sweet and sour products such as pickles where vinegar is in

covering liquid: it acidifies diced vegetables previously worked with

salt. The salt breaks the plant cells on the periphery of the vegetable, which leads the way

so that the vinegar penetrates. The preparation is carried out in several stages. Meadow

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salt treatment can be carried out either by the direct application of salt (pickles) or by

brine, salted water followed by rinsing (onions, garlic). A second pre-treatment in

cold maceration (marinade) made of vinegar, water, sugars, herbs, spices ...

allows the acidification phase.

Chutneys, ketchups, onion confits: the acidity of the vinegar goes into the

vegetable during cooking.

Vinegars can be white vinegars (the most neutral), apple cider vinegar,

wine vinegar. The degrees noted on their containers correspond to the acetic degrees

and not to the degree of ph.

Adding lemon juice to our preparations can also help reduce pH; in

cannery citric acid is widely used, it easily allows to reach a ph

of 4.5.

Acidification can also be obtained by the principle of lacto-fermentation: by a

saline brine promotes the development of lactic acid bacteria which by producing

lactic acid acidify the environment and neutralize the growth of bacteria


Acidification can also be provided by fruit juice or wine.

The ph is for products that contain water, oil does not contain water, oil

is a "packaging", it is an anaerobic conservation, certain bacteria

pathogens develop anaerobically.

Below 4.5 ph, the development of pathogenic bacteria is neutralized.


Canned and semi-preserved

Pasteurization, semi canned.

Its purpose is the destruction of pathogenic and spoilage microorganisms. The technique

used is to subject the food to a temperature between 85 ° C and 100 ° C

for a determined period of time and suddenly cool them. Advantage of this method: it

preserves the characteristics of foodstuffs, in particular their flavor. Foodstuffs

pasteurized have a shelf life (shelf life) and should be kept in a cool place.

While a vegetable is cooking, from 63 ° C, pasteurize, but if you want to keep it

must destroy the microorganisms of the surfaces of the jar and the air of the jar, from which we make a

bain marie to preserve.

The altitude of the place where one is located plays on the boiling point, the water boils at 100 ° C at the edge of the

sea, at an altitude of 1200 meters it will boil at 93 ° C, hence the importance of having a


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Pasteurization does not destroy spore-forming (heat-resistant) bacteria.

Sterilization, canning

This is a heat treatment at temperatures above 100 ° C aimed at destroying

any microbial form, which ensures the stability at room temperature of the food.

This treatment can only be carried out with an autoclave (professional equipment), our

domestic appliances cannot achieve temperatures above 100 ° C.

Clostridium botulinium is a bacteria that lives in the soil, we eat every

days in our fresh vegetables and this poses no health concerns, in small doses it

does not impact our health. However, this bacterium which lives anaerobically, if it is

found alone in a jar, it will proliferate; and during her activity, she will release

a toxin which is dangerous and fatal for humans: botulinum toxin. It is

a toxin that paralyzes the organs (it is found in botox injections !!).

The problem is therefore not the bacteria itself, but the toxin it produces.

Botulinum toxin does not resist above 70 ° C, which is why the risks are reduced

when we reheat a can before eating it. So, for example, the

canned green beans is safer in a hot dish than in a salad.

Focus on the pesto

A fresh pesto is a perishable product: it should be consumed within 3 weeks and

kept cool.

A pasteurized pesto (20mn in a pot) remains a product of short conservation, it is

keeps in the fridge for 2, 3 months.

We will seek to reduce the bacteriological risks:

The presence of pine nuts, or other nuts, or traditionally

Parmesan cheese or other very dry cheese, increase the rate of bound water

(water bound to organic matter) in relation to the rate of free water (water not bound to

organic matter, conducive to bacteriological development).

The leaves are carefully cleaned, bleached and dried.

The addition of lemon juice helps lower the ph.

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