Vacuum Process and Cooking Pouches

Vacuuming and sealing food in a pouch requires 6 steps:

1. before vacuuming food, take care it is at fridge temperature,
2. choose the right cooking pouch that meets your needs,
3. position the pouch, clean and flat on the sealing bar of your vacuum machine,
4. vacuum and seal the pouch,
5. check the quality of the vacuum in the pouch and the seal,
6. mark the date and contents of the cooking pouch.

In Europe (and in particular in France) it is not necessary to obtain an administrative authorization to vacuum pack food, except in the case of take away meals for which you will need a specific room and authorization. In all cases, the Good Practice Guidelines indicate that training is recommended in order to learn the techniques and the rigor necessary for the vacuum process.

​It is crucial that food about to be vacuumed isn’t warm. The food should be at room temperature, best below + 4°C or fridge temperature.
The reason is, water in hot food, while vacuumed, will tend to reach the boiling point very quickly.
This boiling point causes 3 problems:

- it generates steam which will get inside the oil of your vacuum chamber machine. The oil of your pump will then have to be dehumidified at the condition your vacuum machine benefits from such program. Otherwise, it could cause the motor of the pump to fail.
- boiling can cause the pouch to move during vacuuming and impact the quality of the seal. It is recommended to use long pouches, especially when vacuuming very juicy products or marinades,
- the boiling of a food may be unwanted and damage the cells of a particularly fragile food.

Vacuuming liquid is problematic because liquids tend to come out of the pouch. Then there is a risk the liquid enters the pump of the vacuum machine and cause a failure.
As indicated above, a liquid (same any foodstuff) to be vacuumed sealed must be cold in order to delay as late as possible its boiling point caused by the drop in pressure in the chamber of the vacuum machine. Coldness also increases the viscosity of the liquid which will have less tendency to get out from the sachet. It is recommended to place a tilted insert plate in the chamber of the vacuum machine so that the liquid has more difficulty, under the effect of gravity, to go back up in the pouch.

Professional cooking pouches all look the same but do not have the same technical specifications and qualities. You will have to look carefully at the technical sheet of the pouch which will contain the results of the migration tests. The main criteria for defining a cooking pouch are:

- number and type of layers making up the pouch:: the words «PA/PE»indicate the composition of the plastic layers of which the cooking pouch is made. PA relates to the outer layer of the pouch which is made of Polyamide. This material makes the pouch waterproof.
PE relates to the inner layer of the Polyethylene pouch. This material allows the pouch to be sealed.
- thickness of the pouch in microns: a thickness of 80 to 90µ for storage and cooking pouches, 60 to 70µ for schrink cooking pouches.
tubular or 3 welds,
- impermeability of the pouch to air (PA layer),
- suitability and duration of resistance of the pouches to high and cold temperatures.

- Pouches for storage purposes: they are inappropriate for sous vide cooking. While these sachets may indicate resistance to 80°C for example, they have not been tested and validated for cooking at 80°C. Pouches for storage purposes can be used after cooking to preserve the preparations, only. Usually these pouches are thicker than regular cooking pouches and can have a thickness in the range from 110 to 130 microns.

- "Regular" cooking pouches (or boilable cooking pouch): as the name suggests, you can cook food in this type of pouch. Some cooking pouches can be exposed to temperatures of up to + 121 ° C for a limited time, for example during a 5-minute pasteurization in a combi-oven. These pouches are also perfectly suited for cooking in a bain-marie. Often, these pouches can also be frozen, or even deep frozen, then can be reheated in a water bath. Cooking pouches generally have an excellent oxygen seal, which allows you to cook and store your vacuum-packed products in the same pouch.

- Schrink cooking pouches: they are recommended for food that must keep the shape during and after cooking (foie gras, pigeon, ham for example). Most shrink cooking pouches also benefit from an excellent barrier to oxygen and thus allow very shelf life and storage after cooking.

- Other containers to cook sous vide: sous vide cooking in jars has many advantages and is more and more popular with professionals. All you have to do is place the jar with its lid in the vacuum chamber machine and then start the vacuum process. The lid of the jar will be closed automatically. Training is required for this type of cooking.

You don't need to puchase a lot of pouches references. Often 3 sizes per type of pouch are sufficient… Below you will find some tips to help you choose the right dimensions for your cooking pouche.

Regular cooking pouch (NON schrinkable pouch):
The width of the pouch will be approximately equal to the width of the product + its thickness + 2 to 4 cm.
The length of the pouch will be approximately equal to the width of the product + its thickness + 7 cm minimum.
In order to obtain a good seal, it is recommended to choose a pouch length 20% longer than the calculation recommended above. This is especially necessary when vacuuming liquids or marinated or juicy preparations. For example, a food 20 cm long and 6 cm thick should be put in a pouch 20 + 6 + 7 = 33 cm long. For more security, you can then add 20% of length, i.e. 36 x 1.2 = 40 cm, approximately.
Don't be afraid to use a pouch longer than the length of the chamber of you vacuum chamber machine. It is possible to make the pouch protrude from the chamber by making an incision as described in point 3. below.

Non-tubular pouches (pouches with 3 welds):
The dimensions of the cooking pouches given by the manufacturer are the outer dimensions of the pouch. To find out the inner dimensions of the pouch, subtract 8 to 10 mm from the total width of the pouch and 4 to 5 mm from the length of the pouch.

Products with sharp edges or bones: It is recommended to use drop cloths or aluminum foil on problematic areas.

Schrink cooking pouches:
Before cooking a vacuum-packed food in a schrink pouch, it is necessary to perform an intermediate step: the retraction (schrink). This type of pouch shrinks by about 30% when immersed for 5-10 seconds in boiling water. It will take some experimentation to find the right size pouch for the food you want to sous vide.

Vacuuming a pouch longer than the length of the chamber of the vacuum machine: Whether it's to vacuum liquids or to ensure that the bag does not move while vacuuming a foodstuff, it is sometimes preferable use a pouch whose length is greater than the length of the chamber of the vacuum machine. In other words, the pouch will protrude from the chamber when the lid of the vacuum machine is closed and will be unable to move due to the heavy pressure exerted by the lid. Do not forget, before closing the lid, to make an incision in the pouch of about 3 cm (in the direction of the width of the pouch) using a knife.

Before closing the lid of the vacuum machine, don't forget to make an incision in the pouch of about 3 cm (in the width direction of the pouch) using a knife. This incision should be made halfway between the sealing bar and the edge of the lid. If you forget to make this incision, the vacuum will not be created in the pouch.
The pouch must be placed flat and wrinkle-free on the sealing bar.
Pay particular attention to the cleanliness of the seal pouch opening and especially the inside of the pouch. As a reminder, it is the inside layer of the pouch that enables the pouch to be sealed.

Measuring the vacuum in a pouch: the greater the vacuum in a pouch, the less oxygen it will contain. Oxygen allows the development of so-called "aerobic" bacteria and over time alters the flavor of food. The best way to measure vacuum is to use a unit called bar.

1 bar is the atmospheric pressure measured at sea level.
-1 bar corresponds to a perfect vacuum.
-0.99 bar corresponds to an excellent vacuum quality.

On a vacuum machine, the vacuum control can be set either in time (seconds), in percentage or even in mbar if the vacuum machine benefits from an electronic vacuum sensor. For example 99.9% will correspond to -0.99 mbar. To vacuum fragile products, it is sometimes recommended to use the "gradual return to atmosphere" or "gas flushing" option of your vaccum chamber machine. This feature makes it possible to avoid a "slap" of the bag on the product when it is returned to the atmosphere.

After vacuuming, a check of the quality of the vacuum and the weld is required:
- check if the weld is clean and without folds,
- exert pressure with your finger on the vacuum-packed product to check that no air bubbles appear.

Stick a food label on the cooking pouch or write the vacuum date and contents of the pouch directly on the pouch.

In general, to put under vacuum food significantly slows down the development of bacteria and greatly increases the BBD. For meat, it is usual to consider that the BBD will go from 5 to 8 days instead of 2 to 4 days for meats not vacuum packed. Health regulations do not provide BBD for fresh fish. Nevertheless we can say that a fish has a BBD about 5 days at 5°C. This BBD can be multiplied by 2 if the fish is immediately vacuumed packed.
Vacuum packing food also makes it possible to considerably reduce the risk of bacteriological contamination between foods, whether during storage, before cooking, but also after cooking.

The red coloring of meat is dependent on the presence of oxygen in the meat. When red meat is vacuum packed, the loss of oxygen will cause significant discoloration turning from brown to gray. This is normal. When the meat is returned to the presence of oxygen, it will regain its original color.

The so-called "Fruits à couteaux" in French (fruits you peal with knife to eat the immediatly) such as apple, pear...need oxygen for their conservation and ripening. These fruits will therefore be difficult to store under vacuum. However, it is possible to poach this type of fruit under vacuum with a juice or alcoholic sauce (pear poached in red wine for example…).

Sous vide cooking technic can be used to optimize the preservation of a dish. In general, you need to make sure that the shelf life of your dish is safe for the consumer. It is set under your responsibility and should not be chosen at random.
A BBD (Best Before Date) depends on many factors such as the choice of your raw materials (genetics, type of production, transport conditions, etc.), the cooking table applied and respect for the cold chain. The quality of the vacuum and the permeability of the pouch to oxygen have a decisive impact on the BBD of the product. For example, a foie gras cooked sous vide at 58°C in a pouch with low oxygen permeability (<50), will have a shelf life of 21 days minimum. The use of a highly permeable vacuum pouch (>200) or poor hygiene practices can lead to its shelf life being reduced to 7 days. It is therefore necessary to check, at least every 2 years, whether your vaccum chamber machine performs a quality vacuum and to request from your supplier the precise technical data sheets of your cooking pouches.

You should also check if the shelf life of your dish matches those of the cooking tables you have applied. For this it is necessary to do laboratory analyzes. In order to perform simplified analyzes at a lower cost, you must set up a BBD verification protocol. This protocol makes it possible to limit the analyzes to the search for germs specific to the sous vide cooking method (total flora, lactic flora, enterobacteria, etc.) on the basis of three analyzes to be staggered over time. We recommend that you be accompanied in this process by a specialist who will be of great help to you.

There are 2 types of machine for vacuum-packing food: external bag vacuum machines and vacuum chamber machines.
External bag vacuum machines: it is very difficult to vacuum-pack liquids or very juicy foods with this type of equipment. However, you can do this by freezing them first. These machines are suitable for small budgets. You will not be limited by the length of the pouch with this type of vacuum packing machine, however only embossed pouches (structured) can be used. Disadvantage: Embossed pouches are more expensive than the smooth pouches (non structured ones).
This type of equipment is reserved for occasional and non-intensive use. These machines do not require special maintenance.

Vacuum chamber machine: They are professional food vacuum machines, powerful, fast and also allow vacuum-packing liquids. The pouches to be used are smooth and less expensive than structures (embossed) pouches, but the vacuum chamber machine itself is a significant investment in a kitchen. Periodic maintenance should be planned.

This will depend on the power of the pump and the residual air volume of the chamber compared to the space taken up by the food to be vacuumed. In other words, the smaller your food and the larger the volume of your chamber, the longer the vacuum process will be, and vice versa ... Potentially, a good vacuum chamber machine can perform 2 vacuum cycles per minute. You can optimize this frequency by purchasing a vacuum chamber machine with a very powerful pump and reducing the volume of the chamber by using inserts.

The amount of cooking pouch put under vacuum can also be significantly increased by adding several pouches in the chamber using a very wide sealing bar (allowing to position 2 bags for example) or by installing a double sealing bar on your vacuum chamber machine. The control of the vacuum is set either in time (in seconds) or by electronic pressure control (percentage or mbar).

There are several types of welds: single, double, with or without automatic bag cut-off. Double welded systems are very popular. But don't get it wrong, a good quality single weld is better than a medium quality double weld. The quality of a weld will depend on the pressure exerted on it. If you double the weld surface (double weld bar), you'll reduce the pressure exerted on it as much and therefore its quality may be poorer.

Some vacuum chamber machine have a boiling point detection feature. This optimizes the vacuum process and limiting the entry of water steam into the oil pump. It is necessary to vacuum-pack cold foodstuff so that the boiling point occurs as late as possible during the vacuuming process. Other options also exist such as controlling the return of air into the chamber at the end of the vacuum cycle (prevents the bag from "slamming" the food), and the reinjection of gas to create a protective atmosphere packaging.

A vacuum chamber machine is a professional vacuum-packing machine that is subject to significant physical stress. You will need to perform periodic maintenance on your machine. Depending on the frequency of use, it is usually recommended to carry out a semi-annual or annual review by a professional.
Daily maintenance: cleaning the chamber and the lid with a conventional cleaning product and a damp cloth.
Weekly maintenance: run the pump oil dehumidification program. In general, if a vacuumpacking cycle has generated a large amount of steam during a day, it is recommended to start the dehumidification program at the end of that same day. This program involves heating the oil pump in order to extract residual moisture. This program can last between 15 and 30 minutes depending on the machine.

Monthly maintenance: check if the oil level in the pump is correct, if necessary top up with an oil recommended by the manufacturer. Inspect the seal bar to verify if the Teflon tape is in good condition. It may be necessary to change the Teflon tape or the solder wire. The silicone seal on the lid may also need to be replaced.