Some while ago I linked to a FAO based document on evaluating the viability of small scale drying of tropical fruits.
Now I am linking to a very comprehensive document on Processing Aspects of running running such a business.
This is an incredibly detailed, systematic and detailed document that will ensure the processor is able to run a business that produces quality and safe solar dried products.
It covers the range of issues including:
Solar drying techniques
Meeting custmer requirements
Hyginene and food safety
Procurement and storage of fresh produce
Operation of the dryer
Management of processing operations
in a simple style which is illustrated by the extracts below on preparing fruit and controlling the drying process.
Cutting and slicing
It is important to cut and slice the peeled fruit to a particular thickness depending upon the kind of fruit being dried, as thicker pieces will dry at a slower rate than thinner pieces, very thin pieces tend to stick to the drying trays and will be difficult to remove, thicker pieces may not dry fully and subsequently deteriorate after packing and packages of dried pieces of varying thickness appear relatively unattractive and may be difficult to market.
The optimum thickness of slice for drying varies for different produce. From experience gained so far with processing operations in Uganda, it is suggested that fruit is sliced with thicknesses as follows: pineapple 2 3 mm, mango 2–3 mm, banana 5mm and tomato 3–5 mm.
Cutting knives and working surfaces need to be cleaned in bleach solution before use. Knives should be kept sharp and fruit handled as gently as possible during cutting to minimise further bruising. Slices should be placed in clean bowls which have been rinsed with clean water, ready for loading onto the drying trays. For tomatoes, it is better to place the cut slices directly onto the drying tray.
Any bruised or otherwise damaged pieces should be removed at this time since they will result in a discoloured and unsaleable product. Their removal at this stage, rather than after drying, will maximise throughput and hence profitability. Bruised and damaged fruit should be disposed of with the peelings. The stones from mangoes should be similarly discarded.
Before loading the trays, they need to be brushed clean and washed free of debris before being used.
Key points on cutting/slicing operations
>Wash hands in clean water using unperfumed soap
>Ensure slices are of the correct thickness and even
>Discard any damaged or discoloured slices
>Handle slices with care, store slices for drying in clean bowls.
During the first few hours of drying, particularly during very hot and sunny weather, fruit may dry at such a rate that moisture condenses on the inside of the plastic covers. This can be avoided by opening the loading doors slightly (20 mm) to increase air circulation, but covering the gap with mosquito mesh. This will only be necessary, if at all, during the sunniest part of the day (10:00 to 14:00), and only during the first day of drying. Doors should be kept open only for a minimum period of time and closed again as soon as the weather becomes cloudy. The loading doors should never be left open during the night.
In poor weather, drying will stop. If it rains, it will rapidly cool the dryer and this will usually result in the cover fogging over due to condensation. It will be some time before the dryer will start to work again once the sun returns. Ideally, putting a portable, locally-constructed thatched cover over the dryer in poor weather will help operations. (This can also be used when the dryer is not in use to help protect it and prolong its life).
Under fine and sunny conditions, the fruit slices should be dry after two full days in the dryer. However, it is essential to test slices; if they are not sufficiently dry, they will become mouldy and completely unsaleable in a short time. Judging dryness is an Important skill and not an easy one to describe; it is easier to show. As a check, several slices should be removed from the dryer and allowed to cool for several minutes. The fruit may be sufficiently dry if it is not possible to squeeze out moisture from the slices, tearing a piece in half, the middle is no longer moist and slices are kneadable and pliable, but do not stick together. If the slices are not properly dried, drying should be allowed to continue for one to two hours and then checked again.
The final moisture content of the dried fruit should be around 10% (on a wet basis). Simple, low cost equipment is not available for measuring moisture content, but it is critical to achieve a low final moisture content for safe long-term storage. The buyer of the products will check it as a critical factor when assessing quality. This is particularly the case if the products are to be sold into export markets; poorly dried products will undoubtedly result in future loss of sales to buyers and consumers.
Key points on drying operations
> Open doors if moisture condenses on covers for short times only (the gap should be covered with mosquito mesh)
> Check slices are dry before removing trays
> Never leave loading doors open at night
> Prevent insects entering the chamber.