In 1919, the Middlesbrough Cooperative Society purchased the mill building and replaced the waterwheel with a water turbine that provided electric light and power. The turbine was powered by water from the mill race. The Cooperative Society converted the mill into a milk processing plant that could pasteurise up to 500 gallons of milk a day and turn it into cheese that was taken to Aysgarth railway station for onward transportation to Middlesbrough. However, the operation must have been uneconomic because Middlesbrough Cooperative Society’s ownership of Thoralby dairy was short-lived: in April 1922 the Society offered the mill building for sale, as shown in this advert.

Thoralby Mill Dairy and Electricity Generating Station

Alfred Rowntree, who owned Coverham Dairy, purchased the mill building. He continued operating the dairy and set up a piggery alongside the mill building, feeding whey from the cheese-making process to the pigs. Notice the cheeses on the table in front of the building. Rowntree used the turbine to generate electricity that powered the dairy machinery and supplied lighting to Thoralby and Newbiggin. The water to power the turbine entered the mill via the launder that had previously fed the waterwheel. The dairy had ceased operation by 1948 when electricity generation was taken over by the national grid.

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Darlington & Stockton, 1923

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​THORALBY MILL, which a few weeks ago was purchased by Mr. A. Rowntree, of Coverham, is already in the hands of the builders. The old wheel which has done duty for so many years, has been taken out, and also the millstones, the latter going to their old owner, Mr. Sayer, who hopes to use them again in a new home. The water power is to be used for an up to-to-date electric plant. It is hoped that both Thoralby and Newbiggin will be able to have electric light by autumn next. The dairy, it is hoped, will be ready to start in the early spring. Mr. Rowntree is putting down an efficient sewage plant, so that the Beck may be kept pure.