English 
Zhengfeng Road, Licheng District, Jinan City, Shandong Province,China
Author: Alex Song Publish Time: 2026-10-29 Origin: Site
A vacuum pack is often described by how hard the lid pulled, but that reading describes the chamber, not the pack. What survives inside the bag is a small volume of gas, and the oxygen in that gas is what the product reacts with. Two packs can leave the same machine on the same afternoon, show the same chamber reading, and behave completely differently a week later, because the amount of gas left in the headspace, the film around it and the temperature the pack saw afterwards are three separate variables.
This matters for buyers because the machine can only control the first of them. Understanding where the machine stops and where the process takes over is the difference between a line that holds its shelf life and a line that is blamed for something it was never able to fix.
It is also why vacuum figures quoted across suppliers cannot be compared directly. A number given as a chamber pressure says nothing about how long the pump was allowed to run, whether the product was outgassing during that time, or what the pack was like when it left the bar. Two machines quoting the same figure can leave different amounts of gas behind, and a buyer who compares only the figure is comparing the wrong thing.
Residual oxygen. Fat oxidises, pigments change and aerobic spoilage organisms grow in proportion to the oxygen available. This is the variable most often quoted as "vacuum strength", and the one most often left unmeasured. A pack is not assessed by the gauge; it is assessed by what is left inside it.
Water activity and pH. Two products with identical oxygen levels will not last the same time if one is a dry cured sausage and the other is a fresh fillet. Vacuum packaging slows the organisms that need oxygen and favours those that do not, so the product's own chemistry decides which group is being held back.
Temperature history. A chill chain is cumulative. An hour on a loading bay is not recovered by an hour back in the chiller, and no machine setting compensates for it. This is usually the largest uncontrolled variable in a plant that has already bought good equipment.
Film barrier and pack geometry. The film is not a wall, it is a retarder. Oxygen crosses it continuously, faster through thin film, faster at higher temperature, and faster when the pack has a large surface area for its volume. Headspace volume sets how much gas has to be dealt with in the first place.
Pushing the chamber harder sounds like the safe choice. In practice it creates three problems. Water held in the product starts to evaporate under low pressure, so the pump spends part of the cycle removing vapour rather than air, and the reading improves while the oxygen left behind does not. Soft product compresses and deforms, which ruins appearance and, on bone-in cuts, drives sharp edges into the film. And liquid is drawn towards the opening, where it sits in the seal zone exactly when the bar comes down.
The correct setting is the one the product tolerates, not the one the pump can reach. That is why the same model behaves differently across a product range, and why a machine quoted on maximum vacuum tells a buyer almost nothing about performance on their own product.
A seal is a weld, and welds have a width. On the DZ-600/2S double chamber vacuum packaging machine the bars are 600 x 10 mm and there are two of them, so two packs close per cycle at a fixed seal width. That width is a design decision, not a setting to be tightened later: narrow seals tolerate less contamination and less film variation.
Most seal failures are not machine faults. They are product in the seal zone, fill level too high for the bag, or a bag too large for the chamber so the neck folds under the bar. Chamber size therefore belongs in the seal conversation, not only in the throughput conversation, because a bag that has to be forced into the chamber will fold at the seam.
Two checks catch most of it before dispatch. Look for channels or bubbles along the seal, and pull the seal apart by hand to see whether it fails at the weld or beside it. A seal that peels cleanly at the weld is a sealing problem; one that tears the film is usually a sound seal on a thin film.
Bag gauge is the other half of this. A heavier bag resists puncture on bone-in product and holds a wider seal, but it also needs more heat to weld, which is why a bag change is a machine setting change and not a purchasing decision made in isolation. Where the same line runs several products, keeping one bag family and adjusting the bar temperature is usually more repeatable than stocking three gauges.
Modified atmosphere packing replaces the air with a chosen mixture after evacuation. The machine still has to remove the original atmosphere first, which is why the MAP and skin tray sealer pairs a vacuum stage with a gas mixing stage rather than simply flushing over an open tray.
The mixture is a trade-off, not a recipe. Keeping red meat looking red requires oxygen, and that same oxygen is what oxidises fat and shortens the window on fatty products. Reducing oxygen protects fat and colour stability but shifts the appearance of fresh red meat. Neither direction is "better"; they answer different retail requirements, and the mix has to be chosen against the product and the display case it will sit in.
Skin packing removes the argument altogether. The film is drawn down onto the product so there is effectively no gas pocket left to collapse or to migrate, and the pack becomes a different physical proposition from a tray with a domed lid. On the TDMFT-690 tray sealer this runs at three trays per cycle on 710 mm roll film, four to eight cycles a minute depending on tray and product, with a maximum mould size of 690 x 375 mm.
On the specification, four numbers decide whether the machine fits the job: chamber footprint against the largest pack, seal bar length and count against packs per cycle, cycle rate at a realistic load rather than at its best case, and film format. Compressed air demand belongs there too, at 0.6 to 0.8 MPa on the tray sealer, because a line that cannot hold air pressure will not hold cycle rate.
After installation, four measurements belong to the customer, not the supplier. Residual oxygen in a sample pack, seal integrity by peel and visual check, leak rate on a held pack, and product temperature at the moment of packing. Those four describe the process. The machine only makes them repeatable.
The chamber vacuum packaging machine range covers bag-based packing for whole muscle, bone-in cuts and irregular product, at three to five cycles a minute with two seal bars on the double chamber models. Where the pack shape is fixed and the film forms the base, the thermoforming vacuum packaging machine range is the other route, and the packing machine category sets the three formats side by side.
What no supplier can give a buyer is a shelf-life figure for their product. That number comes from the buyer's own trial, on their own product, through their own chill chain. What the machine can do is remove the variation that makes such a trial unreadable.
