Growing our own potatoes in Scotland
This season we have grown 110 acres which will produce approximately 2200 tonnes of raw material. This will produce about 3.6 million big bags of crisps!
Main varieties used are Lady Claire and Lady Rosetta. A trial has been done with a variety called Mustang this year also. We print the type of potato used on the back of the packs beside the “best before” information. Potatoes are a natural product and will of course have to have some variation in size or other qualities and we work to produce optimum conditions to create as many which are perfect as we can.
We are pleased to have proven that good crisping potatoes can be grown in Scotland – and we have grown ours on land from Kinross in the south to St Cyrus (Aberdeenshire) in the north. Careful choice of land, the weather, planting and care of the growing plants all contribute to achieving the right balance of size, dry matter and sugar. The choice of field is important with a preference for lighter (sandy) type soil – so many of our fields are on the coast.
Seed quality is important, as is the spacing and depth of seed tubers. The spacing ensures we get the size of crop we are looking for (32mm x 80mm) and the correct depth ensures we avoid in field greening. Potatoes which are too big make crisps that are too big – it’s no good if they won’t fit in the bag –or if they did, you’d only get 2 or 3! On the other hand, if the potatoes are too small, then you may feel disappointed not to find any champion big crisps in the bag. We need to find a balance and will grade the potatoes on the way into the factory to have most at the optimum size.
There is quite a lot of water in a potato which evaporates in the cooking process – so the amount of dry matter determines yield (the amount of potato crisps you get from a potato). We are aiming for a dry matter of 22% plus and zero sugars The sugar level determines fry colour – too much sugar and the crisp looks brown or burnt. As much natural senescing of the crop as possible ensures that we maintain dry matter and sugar level and then storage conditions are crucial to keep the sugar levels low.
The skins on the crop must be fully set before we lift to avoid damage.. Immature crop will not keep in store. Gentle lifting is critical as the high dry matter also leads to potential bruising. We use specially made cushions to avoid drops into the 1 tonne wooden storage boxes.
These boxes are transferred into temperature controlled stores and held at precise temperatures.
Crop will generally come into store between 15-20 degrees. A curing period then begins which involves bringing the temperature down by 0.5 degree/day until we reach optimum holding temperature which varies dependent on the potato variety. Fresh ambient air must be circulated within the store daily to ensure we don’t have a build up of CO2.
We learn more about crisping potatoes in the factory every day. We also invest in research to find a brand new variety of potato which is absolutely perfect for making Mackie’s crisps.