Icy Herbs - building quality in the mountains

By Dr Garth Cambray

Adding value to agricultural products is the only way to stay competitive in the global economy. In this article we see how Icy Herbs in South Africa breaks new ground in the production of snap frozen organic herbs.

A centre pivot irrigated basil field.

High in the mountains of the Eastern Free State Flip Minaar, a farmer and agricultural engineer has used ingenuity and science to perfect a way of freezing herbs so that the freshness stays in, allowing fresh herbs to be available 24 hours a day from your freezer.  

If you freeze plant matter, such as say a bunch of parsley or spinach, it normally reduces the leaves to soggy blackened blobs. As water freezes it expands and crystallizes. If one looks at the structure of a cell it has a cell membrane and then various bodies within the cell which are also enclosed by membranes. Some of these contain powerful enzymes, which if released into the cell digest and destroy it. As the cell freezes the membranes, which are made up predominantly of lipids (fats) become more rigid and the ice crystals punch holes in the membranes. When the cell thaws out, these holes allow the contents of the cell to mix and rapidly digest itself, going soggy. Enzymes such as hydantoinases then cause browning reactions which darken and spoil the colour of the now soggy plant. In short, freezing spinach or lettuce is not an ideal way of preserving these plants.

A dill field

An alternative to freezing is snap freezing, where the temperature of the cells is dropped so fast that the water does not have time to crystallize - snap freezing can therefore actually just freeze live viable cells in a state of suspended life. When they thaw out they are almost exactly like they were when frozen.

Flip and Riana Minaars primary business was the production of herbs for extracting essential oils. Taking the premium grade herbs and freezing them for export however presented a challenge. Blast freezing plants in Europe  usually use liquid ammonia based refrigeration systems to produce super cooled air which is then forced past the herbs freezing them in three or so minutes. A great idea, but a super cooled air freezing plant would cost in the region of $8 million. Flip Minaar put his understanding of agricultural engineering to good use determined to design a low cost system able to produce better quality herbs.

After careful initial experimentation they determined that liquid nitrogen froze the herbs faster than super cooled air and produced a better quality product. The next step was to design a system capable of handling large volumes of herbs - this is now done in a freezing tunnel with liquid nitrogen. The advantage here over super cooled air (-40º C) is that liquid nitrogen has a temperature of -196º C meaning that the herbs freeze perfectly in three minutes. And thus the company Icy Herbs was born.

Parsley and the processed frozen chopped parsley

The farming operation has produced up to 300 tons per annum of herb matter for sale, with 60 % of this being basil and the remainder being Parsley, Thyme, Coriander, Fennel, Rosemary, Oregano, Tarragon, Chives, Garlic Chives, Sage, Spearmint, Dill, Rocket and Marjoram. But the story goes beyond getting the thumbs up for a quality product both in the South African and EU markets, its also about how science can help create jobs. 

The farm currently employs 11 people in the freezing and packaging line and approximately 100 agricultural labourers on a varied schedule in the fields.


December 2006