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At Potatoes New Zealand, we often get asked questions about potatoes and here are some of the answers to those questions.

  1. Why do potatoes go green?
    Greening is caused when potatoes are exposed to light. The greening is due to the presence of a substance called solanine, which is poisonous. If there is only a small portion of the potato that is green, simply trim it off and discard.
  2. Why do some potatoes go grey when they are cooked?
    This is related to the iron content of the potato. At certain times in the year the iron content of the soil varies, hence when the iron content is low the potatoes tend to grey if they are cut open and/or cooked and left at a high temperature. To rectify this, add some lemon juice to the water and this will inhibit the greying.
  3. Why do potatoes vary?
    The growing conditions of a potato greatly influence the characteristics of a particular potato. A similar potato which is grown in different conditions, i.e. rainfall, frost, soil type, can exhibit quite different qualities in terms of cooking attributes, flavour, etc.
  4. If I select a potato variety I really like, why does it cook, and sometimes taste, differently from time to time?
    This is simply the nature of the potato, and it is why, as an industry, we are reticent to make a claim about a particular potato variety and its performance. See seasonal changes.
  5. I have heard potatoes described as waxy and floury, what does this mean?
    Basically, there are two main parts of a potato – water and starch. The more starch in the potato the ‘flourier’ it is, and the more water, the waxier in texture. The amount of water and starch affects how the potatoes cook. A potato with lots of starch goes really fluffy and soft when cooked -so it is ideal to mash or bake. A potato with less starch has a waxy, more solid, texture when cooked making it ideal to boil or use in salads. Some potatoes have moderate amounts of starch. These potatoes fall into the ‘general purpose’ category and will tend to perform most tasks, although perhaps with not as good results as the ones which clearly fall into the floury or waxy category.
  6. Why do some potatoes fall apart when boiling?
    Some potatoes retain their shape a lot better than other potatoes, depending on the structure of the potato. Potatoes which disintegrate on boiling tend to be floury – which are better suited to mashing. It is also sometimes due to the cooking technique being too aggressive – i.e. boiling too hard or for too long.
  7. What is the correct way to boil or mash a potato?
    There are as many answers to this question as there are people willing to answer the question! Most people get their favourite way – some will swear that the water must be boiling before adding the potatoes, others are adamant that the potatoes must be added to cold water and bought to the boil. Other experts claim that in order to mash potatoes the potatoes must first be baked in their skin and then peeled and mashed. Some people say that milk or cream added to mashed potatoes must be heated, still others claim that baking soda needs to be added when mashing to make them lighter and fluffier (but this does break down some of the vitamins and shouldn’t be encouraged). It’s up to what you prefer to do! See boiling and mashing for our tips.
  8. Why do some potatoes brown better when making them into fries or wedges?
    This is due to the sugar level in the potatoes. Potatoes with a naturally high sugar level will brown a lot faster that those with a low sugar level. This is why processing manufacturers are particularly careful to monitor sugar levels. Sugar levels are higher in new potatoes before the sugar is converted to starch.
  9. Why do some potatoes have a hole in the centre?
    This is called hollow heart. You sometimes see this in small potatoes, but it is much more likely in large or over mature potatoes. They are safe to eat.