Leafy herbs will deteriorate if not cooled quickly.
Product deterioration is broadly a factor of heat multiplied by time. The table below gives a guide to the deterioration of product at 25 degrees C, compared to product that has been immediately cooled to 4 degrees C.
| Produce Temperature (degrees C) | Time (hrs) To Reach Same Point Of Deterioration |
| 25 | 4 |
| 4 | 25 |
Thus, rapid cooling technologies can increase shelf life, product colour and quality, whilst reducing growth of pathogenic bacteria such as E. coli and Salmonella spp.
Water
Vacuum cooling works by evaporating a small amount of water from the surface of the produce, so dew and water droplets on the leaves will be dried off when the herbs exit the machine, meaning leaves can be dispatched immediately to customers.
If the herbs have dry leaves, then in crate drenching (spraying the leaves with a fine mist of water) is recommended. This added water is evaporated away in the vacuum cooling process, creating the cooling affect without reducing the moisture content of the leaf itself.
Outer leaves freezing?
The control system on our machines prevent the produce freezing.
Older vacuum coolers often had rather crude control systems which couldn’t get even temperatures through the different parts of the produce, and could often freeze the outer leaves whilst trying to achieve the set temperature for the core of the plant.
Our unique control systems work precisely and intelligently to set a minimum temperature for any part of the leaf so it isn’t possible for the leaf to freeze, whilst also achieving uniform temperature throughout the produce.
If the thicker parts of the produce are not cooled sufficiently, the latent heat will be ‘released’ back to the leaves, resulting in a lower quality and shelf life of final product.
We can convert older machines to our modern precision control systems. Please contact us to discuss how this might improve your leaves.
Herb specific programmes
Different herbs can require slightly different cycle programmes.
With the option of a touchscreen controller, operators can choose the required programme for a specific herb at the touch of a button. This achieves consistency between different operators and reduces the time needed for staff training.
Vacuum chamber
It is important to size the vacuum chamber to your pallet size and height, as well as your required daily requirements (number of loads per day). Standard sizes usually revolve around 1.0 x 1.2 x 2.4m pallets, but we manufacture to suit any size. You don’t want to be unstacking trays!
The tighter the fit of the pallets in the chamber, the less air there is to vacuum out, and the quicker the cycle times.
Vacuum pumps
We only use Busch vacuum bumps. Less expensive alternatives are available, but we would only recommend fitting Busch pumps.
Vacuum pumps need to be sized correctly depending on chamber size and the type of produce being cooled. If considering a new vacuum cooler, please do always compare the brand and capacity specified. Undersized vacuum pumps will mean slower cycle times and cause problems with the pumps. The pumps are only designed to run at full capacity for a short length of time, so if a manufacturer has fitted undersized pumps (to make the vacuum cooler cheaper to supply) they will be running for longer times and will not have the desired longevity.