BBC4’s ‘Winter Walks’ series has been wonderful slow TV, just perfect comfort viewing. If you have missed out, then search winter walks on BBC iPlayer. The series has reminded me how much I enjoy walking in the Yorkshire Dales no matter what the season or the weather.

When I am out in the Dales at this time of year, I am much more observant of the rocks and crags which give us a glimpse of the underlying geology, as well as the man-made structures, such as stone walls, field barns and lime kilns.

Most of the small, isolated drystone structures we recognise as lime kilns today in the Dales were built between 1750 and 1850. Occasionally freestanding but often built partly into a hillside with a deep bowl at the top and a large, arched opening at the front.

Kindling was laid in the bottom of the kiln, above which there were alternating layers of crushed limestone and fuel, often locally mined poor-quality coal or occasionally wood or peat. Once lit the fire would burn for 48 to 72 hours, or longer with further additions of limestone and coal from above.

In the Dales, the quicklime produced would have been slaked with water, to form lime or calcium hydroxide and used in small amounts for mortar, plasters, limewashes, renders, and in the tanning of leather.

However, most of the quicklime produced was used to improve or ‘sweeten’ grassland. Although the underlying bedrock is limestone, soils across the Dales tend to be acidic - ‘soupy’ to the farmer, with low levels of nutrients and high moisture levels. To bring such soils up to productive pasture, especially of intake land and reclaimed moorland during the enclosures of the eighteenth and nineteenth centuries quicklime was added to the soil. The accepted way to do this was to lay the quicklime in small heaps across the field, often covered with soil. These were left to stand to allow rainwater to slowly slake the lime, making it more readily absorbed by the soil. This reduced the acidity of the soil, as well as improving its aeration, and increasing the bacterial and microbial life, important for soil fertility.

When you are next out for a winter walk in the Dales, compare the green grass of lime-improved enclosures and how it contrasts with the brown of the moorland above the intake on the open fells.

Finally, “happy winter walking, watching from the comfort of your own home or better still up in the Dales”.