Most people given a choice would prefer the taste of fresh ground coffee rather than instant freeze dried coffee but nonetheless the freeze dried coffee market is vast both domestically and commercially. It's sheer convenience and ease of use is probably its main advantage and with the improvements of modern production processes the flavour of the final beverage has improved dramatically. Just add a spoonful of freeze dried coffee granules to a mug, add hot water and you can enjoy a decent cup of coffee. We have all probably drunk freeze dried coffee at some stage, but what actually is it and how is it made? Initially fresh brew coffee is made in the usual way using a very large industrial bulk brewer in which very hot water is passed though fresh coffee grounds in a filter system to produce the hot coffee liquor we are all familiar with. This coffee liquor is then concentrated through a series of evaporators under vacuum where some of the aroma and flavour compounds are also removed and stored. This ensures that some of the flavour and aroma of the coffee that is lost during the freeze drying process can be 'put-back' into the final product just before packing.
The concentrated coffee liquor then moves on to the actual freeze-dry processing equipment. Here the coffee liquor is initially foamed and then frozen to a temperature of -450 degrees centigrade. It is then ground to the required particle size. The ice crystals that formed in the freezing process from the water content in the beverage are then removed in a process called sublimation.
Here the frozen granules are subjected to a high vacuum which results in much of the water ice content to be transformed directly into gas (without a liquid stage it would normally undergo) before being returned to room temperature. The finished product usually contains between 3 and 5 percent water. The more volatile flavour and aroma compounds extracted at the initial brewing stage are then returned to the dried product just before packing. As you can imagine an industrial factory producing freeze dried coffee produces vast amounts of used coffee grounds in the production process, but these are not put to waste. They are usually sold on as animal feed, compost or organic fuel. Freeze dried coffee is considered to be of superior quality to spray dried coffee which is made by a different process.
The spray dried production of coffee will be the subject of another article.
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