Well found in the kitchen of My-personaltrainerTv. Today we will be dealing with a rather thorny theme, often unfortunately underestimated: the preservation in oil of food.
Among the most felt dangers there is intoxication with C. botulinum, an anaerobic bacterium with spores resistant to high temperatures, capable of producing a potentially lethal neurotoxin. Let us remember briefly that spores are particular forms of resistance put in place by bacteria to survive even in unfavorable conditions. But let's proceed step by step.
Can oil be considered an effective and safe preservative agent?
Yes why...- Reduces the availability of oxygen to aerobic bacteria
- Limits contamination of volatile bacteria
- Insulate food from the surrounding environment
No because...
- Has no effect on anaerobic bacteria (eg botulinum)
The solution is to subject the food to be preserved in oil to particular treatments, able to guarantee its microbiological healthiness (eg acidification, salting, pasteurization).
Continue reading the article or watch the summary video on preservation in oil.
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X Watch the video on youtubeWhat is the danger of inadequately treated food preserves?
The dangerousness of the Botox is in its relative invisibility ; in fact, the characteristics of the contaminated product are not significantly altered, therefore it is difficult to realize the deterioration of the food.
Botulinum spores are not dangerous in themselves. The problem arises when, in particular conditions (eg absence of oxygen, high availability of water, high pH) the spores germinate in vegetative cells, therefore in live and active bacteria responsible for the release of the toxin.
To understand the danger of botulinum toxins, just think that only 1 gram is able to kill 10 million people!
Please note
To make food preserves safe, it is therefore important to LOCK or PREVENT SPIN GERMINATION.
How to prevent spore germination in food preserves?
The risk of botulinum spore germination is not limited to foods in oil, but may also involve other types of food preserves.
To reduce the risk of botulism, it is important to create an environment unfavorable to spore germination; this result is obtained through specific treatments, such as:
- Acidification (pH <4.5): method that involves boiling or scalding the food in an acid solution (composed of water and vinegar or only vinegar). The scalding guarantees an optimal consistency of the food, while the acidification (ie the reduction of the pH below 4.5) is an indispensable practice in oil preservation, to prevent the germination of botulinum spores.
- Brine / salting: food storage in salt concentrations of 10-33%. This treatment is ideal for storing certain foods, such as olives, capers and anchovies.
- Addition of sugar (50-60%): essential treatment in the preparation of jams and marmalades.
- Sterilization treatment at 121 ° C for at least 3 minutes. This method, almost impossible to achieve at home, is performed on an industrial level using autoclaves. Similar temperatures tend to destroy all heat-resistant spores, which may be present in the preserves.
Considering that the spores of type A botulinum can withstand temperatures of 100 ° C even for 5 hours, it is understood that the classic home heat treatment of cans in water cannot, on its own, guarantee 100% microbiological safety. When preparing a preserve in oil at home it is therefore necessary to resort to some additional treatments, such as preventive acidification (see below).
- Freezing
- Drying
What are the foods most at risk of contamination?
High risk foods | Low risk foods |
Foods rich in water with low acidity (pH> 4.5):
| Foods rich in salt or sugar, and preserves at acid pH (<4.5):
|
Basic tricks for a safe oil preservation
The first objective that we must set ourselves when preparing a preserve in oil is definitely to prevent or avoid the germination of botulinum spores in vegetative cells. To achieve this purpose, it is necessary to comply with some very important precautions, as described below.
- Accurate CLEANING OF FOOD TO BE KEPT. Spore-forming clostridia occur naturally in the soil, so they can contaminate plants in the form of spores. For this reason, it is important to destroy most of the bacteria in the raw material. The careful cleaning and washing of vegetables are the first two basic precautions necessary to remove any remaining soil. For this purpose, we recommend washing vegetables with water added to sodium bicarbonate or other specific disinfectants; the washing must be followed by rinsing the food in running water.
- Adequate TOOL PREPARATION and containers before food preparation. For this purpose, we recommend washing in the dishwasher or prolonged boiling for 20 minutes in cans (with the respective screw caps) and utensils.
- FOOD ACIDIFICATION to be preserved in oil. The food must be subjected to acidification until it reaches a pH <4.5 by adding acidifiers (citric acid) or blanching in vinegar or in a 50:50 solution of water and vinegar. The ideal vinegar for this treatment is certainly that of wine, with an acidity of 6% or more. If you want to use a more delicate vinegar (eg apple vinegar, with an acidity of 5%) it is advisable not to dilute it in water, but to use it pure.
- TREATMENT OF AROMATIC SPICES / HERBS. Particular attention must be paid to the use of aromatic plants raw-ground in preserved oil: even spices must in fact be adequately treated to reduce the risk of microbial contamination. For this purpose, we recommend using dried aromas; if you want to use fresh aromatic plants, you should instead proceed with the blanching in water and vinegar, and with the subsequent drying in a clean cloth.
- CORRECT DRYING OF FOOD TO BE STORED. After the preliminary treatment in the solution of water and vinegar, the food should be wrung out or in any case dried from excess water. For example, when preserving the aubergines in oil, they must first be boiled in water and vinegar, then squeezed and left to dry in a clean cloth for a few hours, or overnight, in order to remove as much water as possible. Let us briefly recall that the presence of water in the food can facilitate the development of mold, other potentially dangerous organisms for the organism or even favor the germination of botulinum spores.
- FILLING THE AIR SPACES that form in the container of the preserves. During the invasion, it is not rare to observe the presence of small air bubbles trapped in the oil. To fill all the empty spaces, it is good to press the food with a spatula or with a specific press (both tools must undergo preliminary heat treatment in boiling water or in the dishwasher); you will then have to wait a few hours before closing the jar with the cap to favor the air outlet.
- TOPPING. Make sure that the food to be preserved is completely covered with oil. After having filled and waited for the escape of any air bubbles from the jar, it is likely that the oil level has dropped, thus leaving some parts of the food uncovered. It may therefore be necessary to top up or add more oil
- PASTEURIZATION of preserves in oil at 80 ° C for at least 10 minutes; this additional heat treatment ensures the elimination of any botulinum toxins (much less resistant to heat than spores). In oil preserves, where acidity and water scarcity reduce the resistance of spores to heat, a pasteurization treatment at relatively low temperatures (80 ° C) is sufficient for a few minutes.
As an alternative to pasteurization, at the industrial level, the product can be subjected to a sterilization treatment at higher temperatures (121 ° C for at least 3 minutes). Reaching similar temperatures it is certain to sterilize the food (destruction not only of toxins, but also of spores), therefore the preventive acidification treatment described in point three becomes superfluous. Nevertheless, sometimes even the industry prefers to opt for preventive acidification, so as to then be able to perform a milder heat treatment (pasteurization at 80/90 ° C for 10/20 minutes), to the benefit of consistency and properties nutritional properties of the product.
- STORAGE IN A DARK AND DRY PLACE. The oil tends to perish in contact with light: for this reason, it is advisable to keep the cans in the dark or to wrap them with aluminum or dark paper.
How to find out if the food is contaminated?
Before proceeding with the consumption of an oil in oil, it is important to carefully observe the can to ascertain its state of preservation.
Any signs of alteration or deterioration of the preserves can be:
- Swollen metal lid
- Presence of air bubbles rising from the bottom towards the cap
- Opalescent oil
- Unpleasant smell of rancid butter from the preserve
- Alteration of the appearance of the preserved food
Even just one of the aspects listed above should trigger an alarm bell.
However, it should be reiterated that the danger of Botox is also in its relative "invisibility": it is not rare, in fact, that the contaminated food does not show any sign of significant alteration or deterioration. In case of doubt, even with the sole suspicion of alteration, it is recommended not to open nor taste the conserve in oil.
