Churns are machines used for the production of butter from cream or from whole milk. By agitation the butter globules are thrown against each other until after a period which varies in length with the quality of the butter-fat, the temperature, and the condition of 'ripeness,' or incipient acidity of the cream. Churns are of great variety in form and dimensions, from the ladies' glass hand churn producing a few ounces of butter at a time, to one driven by water, steam, or horse-power, and churning the whole milk of a dairy at one operation. The plunge churn or thump churn is one of the oldest and most simple varieties. The common upright hand churn seen in country places is perhaps the best known form of it, but the principle is equally applicable to larger churns. The box churn, either oblong or eubical, is stationary like the latter, the action being brought about by 'dashers' or 'works' made to revolve on a horizontal spindle passing through its centre.
Revolving churns, taking the shape of a box or barrel, are supported from two points on a rigid framework, so that the whole body of the churn is turned round at the rate of forty to fifty revolutions per minute by a crank handle after the fashion of an ordinary grindstone. Sometimes the motion is a simple rotatory one, as when the barrel is supported from the centre of both ends, giving it the position of a barrel rolling on the ground. It may also be hung from two corresponding points, one on each side, and occupy an upright position while at rest. The action is then called 'end over end.' An eccentric motion is given by hanging the body unevenly. These churns also contain 'dashers' or 'diaphragms' which increase the agitation of the cream. Their great advantage is the ease with which they can be worked—a matter of first importance where hand labour is employed. Swinging or 'cradle' churns are increasing in favour, because they are so extremely easily worked, inexpensive, and simple, and because they contain no movable 'dashers,' which demand much care and labour in keeping them sweet and clean. The body, consisting of an elongated box, may be suspended by four chains or thin iron rods, or it may be carried on four flat, flexible iron supports. It is pushed so that it swings backwards and forwards, giving the cream within a course which assumes the form of the figure 8. The Holstein churn is upright and rigid. Its dashers, which are attached to a perpendicular shaft, are worked at high speed. This enables the operator to reduce the temperature of the cream by nearly 10° F., as compared with the temperature at which it is put into an ordinary churn. Churning is then done in summer at 50° F., which gives the resulting butter-product much greater firmness and a better texture. See BUTTER and DAIRY.