There are a few different approaches that may be taken to lengthen the period of time that food can be stored. Drying is one of the earliest means of preserving food, and it predates freezing, boiling, and vacuum packaging by a short amount of time. Drying is also one of the oldest processes for smoking and salting. The innovative process of freeze drying is an alternative to the conventional drying procedures that are typically used to lengthen the shelf life of foods.Because the procedure requires a vacuum at certain points, it can only be done with modern vacuum technology. Freeze-drying food is also only conceivable with this technology.
Freeze drying is a technique that can be used for fruits and berries, in addition to cooked meat and vegetables. Freeze drying is another method that can be used to preserve herbs and spices because it removes almost all of the water content while leaving only a trace amount. It's likely that soluble coffee, often known as instant coffee, is the freeze-dried product that's best known. Meals that are already prepared can be made by simply dissolving the freeze-dried granules or powders in boiling water. Another example of a prepared meal is a canned soup. To dry food, one might conceivably utilize procedures like desiccation, which aren't as complicated as some of the other options. The texture and appearance of the meal will also be altered, which is a downside of this method. The interaction of smells with the oxygen in the surrounding air can also have an effect on the taste.
The cellular structure does not undergo any changes during the process of freeze-drying, and after the technique is over, the desiccated cells can be easily reconstituted by adding water.In most cases, the aromas are kept intact by the use of the vacuum-drying technique.
The process of freeze drying, which is purely physical in nature, makes use of the idea of sublimation. As a result of the drying chamber's vacuum, the frozen water turns into water vapor through a process known as sublimation.Ice does not travel through the "liquid" stage on its way to becoming a gas; rather, it goes directly from the "solid" state to the "gaseous" state.Before beginning the real drying process, the product, whether it be berries, fruit pieces, or coffee extract, must first be flash-frozen in a chilling chamber. This step is required. In order to accomplish this, the product is distributed evenly among trays, which are then placed either directly or on trolleys within the cooling chamber after being positioned there. Following this step, the frozen product is transferred into the actual drying chamber.The drying chambers of certain freeze dryers are designed so that direct cooling can take place there. Freeze dryers are frequently utilized for continuous operations in the food processing industry.
Following the chilling phase, the airtight chamber is put to use for the actual drying procedure, which entails using a vacuum pump to reduce the air pressure within the chamber until a vacuum of 0.5 to 1 mbar is achieved. The temperature range of -50 to -40 degrees Celsius marks the beginning of the evaporation process for the frozen water. The water vapor is extracted from the drying chamber with the assistance of a vacuum pump and then transported downstream to a condenser for further processing. This "ice trap" is cooled to at least -70 degrees Celsius, which allows for the sublimation and condensation of water vapor as ice on the cooling coil. During this stage of the production process, which is referred to as primary drying, the vast majority of the product's moisture is evaporated.
Throughout the process of sublimation, thermal energy is extracted from the drying chamber. It stands to reason that the temperature inside the room will drop while this process is being carried out. As a result, it is necessary to heat up the chamber. It is essential to make certain that, in order to keep the temperature stable or allow for a slight increase up to -20 degrees Celsius, no more thermal energy is added to the water than is evaporated off as sublimation energy. Only this amount of thermal energy can keep the temperature stable.
The majority of products go through a secondary drying process just after the initial drying step. In order to eliminate residual moisture from the product that is bonded to the substance more strongly, the level of vacuum must be decreased to 0.01 mbar or lower, and the temperature must be raised above the freezing point. The dried product, which has a water content of one to four percent, is taken out of the drying chamber once the pressure in the chamber has been brought down to atmospheric pressure. It is then sent on to undergo further processing. Ventilation using dry air or an inert gas is performed so that the dried product does not become contaminated with moisture during the process.
Fundamentally, the following variables affect the freeze-drying process (Fig. 3):
1. Vacuum levels or pressures
2. The Temps
Obviously, the products themselves and their attributes are equally crucial. Because of this, experiments in pilot plants will be conducted prior to commercial freeze drying or prior to drying large amounts of product.
A dependable and finely adjustable vacuum supply is necessary for freeze drying. In industrial food freeze dryers, two forms of vacuum generation have shown their worth:
1.One type of vacuum system includes rotary vane vacuum pumps along with extra vacuum boosters.
2. Systems for creating vacuum that include extra vacuum boosters and screw vacuum pumps
Depending on the size of the drying plant, the items to be dried, and the previously specified physical criteria, one of the two vacuum systems will be more appropriate.
The maximum pressure that rotary vane vacuum pumps can achieve is 0.1 millibar, and they are lubricated with oil.A vacuum booster is recommended while working in the working range of less than 1 millbar in order to achieve a higher vacuum level and to have a sufficiently high pumping speed.
This has the benefit of achieving a vacuum level of less than 0.001 millibar. Moreover, a rotary vane vacuum pump and vacuum booster set together can be made even more energy-efficient than a big rotary vane vacuum pump by precisely tailoring the combination to the size of the freeze dryer.
Last but not least, a vacuum specialist can determine the ideal pump combination. Because rotary vane vacuum pumps and vacuum boosters come in a wide range of sizes, Busch Vacuum Solutions can always provide the ideal vacuum system for any size freeze dryer.
Screw vacuum pumps are capable of achieving an ultimate pressure of 0.01 millibar while operating dry, which means they do not require the use of oil.In addition, a vacuum system that integrates both a screw vacuum pump and a vacuum booster is superior to a solution that only makes use of a single vacuum pump.During the freeze-drying process, a screw vacuum pump can have a frequency-controlled motor attached to it so that the pumping speed can automatically vary to match the requirements of each step of the process. This is done so that the speed of the process can be optimized for the product.
In most cases, one should consult with a vacuum professional before making a decision regarding the vacuum technology and the dimensioning of the vacuum. The response that a trained professional provides will always be the one that is both the most practical and the most cost-effective.Producing vacuum solutions for the freeze-drying of medicines and food items has been one of Busch Vacuum Solutions' primary business activities for a significant number of years. In addition to the vacuum technology, Busch offers all of the essential instruments for monitoring, measuring, and detecting at every stage of the process.