The price of potatoes (Solanum tuberosum) has dropped to Sh1,400 from Sh5,000 per bag in the last three months.
The low price means drastic reduction in farmers’ earnings and losses as the cost of labour, fertiliser and treating of diseases remains high.
As farmers cry foul, value addition is the answer to this challenge. From potatoes, one can make chips, crisps, dehydrated potatoes (diced or sliced), flour, granules, frozen potatoes, flakes, potato puffs, potato “nuts” and grit.
Potatoes can also be made into starch used as a soup and gravy thickener, as well as a meat binder. It has been used in cake mixes, in ice-cream, in fermented milk and in making vodka.
Potato starch has also been used in non-food products such as making textile, glue, ethanol (fuel or industrial grade) and as a substitute for polystyrene disposable plates. Today we focus on making crisps, starting with the requirements.
Four kilos of potatoes should give you 1kg of crisps (eight packets of 125g, which goes at Sh70 each). To fry the 4kg, one would require about half a litre of vegetable oil and 18g of salt.
To get good crisps, always pay attention to the potato variety to avoid ending up with oily, soft, discoloured, hard, partly burned, and blistered product.
Dutch Robjn and Kerrs pink are among varieties that are good for making crisps. The potatoes should have no bruises, injuries or symptoms of diseases. If the potatoes have been stored at 6oC for a long time, they should be conditioned by storing them at ambient (15-20oC) temperature for two to three weeks.
They should be suitable for long-term storage, not prone to darkening either before or after cooking; they should be regular in shape – round or oval; have shallow eyes to avoid waste as you dig them out and have desired flavour, aroma, consistency, texture and colour.
The potatoes should also not be stored in a mouldy atmosphere as they may retain the musty smell and this will affect quality. Insecticides and herbicides residues can also impact negatively on the crisps flavour.
The best potato size for crisps manufacturing should be at least 4-6cm in diameter and not less than 6cm in length. The flesh should be light yellow to yellow but white potatoes can also be used.
Wash the potatoes, peel and then wash again with water before trimming up the eyes and the patches of peels overlooked and any other defects.
Large potatoes should be cut into halves then sliced. Slices should be about 1.2mm each. To protect the slices against browning, wash off the starch.
The knife or slicer should be sharp to avoid potato surface cells being fractured with subsequent tendency of the crisp to absorb oil during frying. The potato slices may also stick to each other resulting in non-crispy product.
To improve colour of the crisps, some additives may be used such as sodium bisulphite, citric acid and or magnesium chloride.
After that, blanch (65-95oC) for a minute or longer using water. This can be done at home by dipping the potato slices in the hot water carefully to avoid the slices clamping together. In the factory, one uses a blancher.
MACHINERY TO DRY CRIPS
After that the crisps should be partially dried prior to frying. This shortens the frying time and avoids oil absorption that would lead to soggy crisps.
There are lots of machinery to dry crisps in factories but at home, one can drain on a wire mesh (stainless steel), air dry or use parchment paper.
The dried crisps are then immersed in hot oil using a wire basket, which will also be used to remove the end product.
Always use oil instead of cooking fat for longer crisps shelf-life. Some fats that have antioxidants may also be suitable as they have been stabilised (chemically treated) and the stability will impact positively on the crisps shelf-life.
The temperature of the oil should be 170oC and crisps fried for 1.5 to three minutes. The colour most preferred is light golden without any browning, over colouring or black spots and traces. Some people prefer darker crisps, which keep the fresh aroma for longer.
Oil temperature is important and use a fryer with marked temperatures. One may also use a catering thermometer, which can show temperatures ranging from 50oC to 300oC or 58-572oF.
Frying at temperatures less than 170oC will increase oil absorption. Too high temperature, for example 200oC, results in browning of the crisps and faster oil decomposition. When frying crisps continuously, it is important to change the oil after 22hrs of use.
The crisps should then be placed somewhere to drain and when excess oil has been removed, they can be salted and or flavoured with powdered onion, pepper, cinnamon, cheese and tomato. They are then packed in heat sealed bags or in air tight containers. If further packaging is required after using heat sealed bags, do it in cardboard boxes because crisps are delicate.
In storage or during retailing, protect the crisps against light, high temperatures and excess moisture. Light promotes rancidity in crisps.
Good quality crisps should have about 2 per cent moisture content. They should be light yellow in colour but darker coloured crisps can also be desired by certain people.
The crispy texture is a quality that cannot be over-emphasised. The crisps should have an oil content of 32-40 per cent. Those with too much fat may spoil easily and those with little fat are usually hard and tasteless.
Dr Ngoda is a lecturer at the Department of Dairy, Food Science and Technology Egerton University.