Potato market requirements
Fresh market potatoes
Tuber quality in terms of appearance and cooking quality is of prime importance to the consumer. Much depends upon variety choice, but also the way the potato is grown.
For the fresh market, tubers need to be consistent in shape and size (45 -85 mm), with good skins that are free of any disease or blemish.
Dry matter (DM) content is also important as tubers with a DM above 18-20% are more susceptible to bruising and may disintegrate when boiled during cooking.
Fresh potatoes are increasingly sold in a range of ‘pre-packs’. Lower priced grades are sold loose or in ‘value packs’.
Processing potatoes
Processing potatoes need to be evenly shaped and of a standard size and quality from one end of the tuber to the other.
For French fries and crisps, a high DM content is needed in order to achieve a good fry colour. Standard colour charts are used by processors to achieve consistent fry colour. In the past, contracts have stated that 18% DM is the minimum. However, industry standards now seek potatoes with a 20-25% DM.
Certain types of sugar - particularly reducing sugars - must also be low, otherwise the French fry or crisp will brown on cooking. Contracts usually specify an acceptable range of reducing sugars.
Processors usually apply contract penalties for losses due to blemishes, bruising, pest damage, greening, growth cracks, etc. A standard contract will specify a maximum of 5% out grade potatoes by weight - i.e. 5kg per 100kg.
Starch production
Potatoes are one of the most important sources of starch worldwide. Variety choice is very important and potatoes with greater than 13% starch content are required in countries such as Germany. The higher the starch content, the lower the waste. Potato tubers contain a large range of starch granule sizes (10-100 mm versus 5-40 mm for cereals) as well as having a high phosphate content. The starch quality influences the final paste properties, especially its viscosity.
Seed production
Crop yields and quality depend greatly upon the health status of the seed. In order that growers can be sure of the quality of their seed purchased some countries have seed production controlled by "Seed Classification Schemes".
Potatoes grown for seed should consist of a uniform grade of small, well-formed tubers - usually 30-55mm diameter size range. Where cut seed pieces are used, fungicides should be used to reduce disease risk.
As a result, the whole growing program, from variety choice, seed spacing and agronomic management, right through to desiccation and storage, is designed to produce a high yield that fulfills the quality requirements of the marketplace.
