Another method that has met with wider acceptance, especially in creameries, is the custom of pasteurizing or scalding the skim-milk immediately after it is separated, so that it is returned to the farmer in a hot condition. In factories where the whole milk is pasteurized, further treatment of the by-product is not necessary. In most factories steam, generally exhaust, is used directly in the milk, and experience has shown that such milk, without any cooling, will keep sweet for a considerable number of hours longer than the untreated product. It is noteworthy that the most advanced and progressive factories are the ones that appreciate the value of this work, and although it involves some time and expense, experience has shown the utility of the process in that a better grade of milk is furnished by the patrons of factories which follow this practice.[4] The exclusion of all danger of animal or human disease is also possible in this way. ~Cleaning dairy utensils.~ The thorough cleaning of all dairy apparatus that in any way comes in contact with the milk is one of the most fundamental and important problems in dairying. All such apparatus should be so constructed as to permit of easy cleaning. Tinware, preferably of the pressed variety, gives the best surface for this purpose and is best suited for the handling of milk. Milk vessels should never be allowed to become dry when dirty, for dried particles of milk residue are extremely difficult to remove. In cleaning dairy utensils they should first be rinsed in lukewarm instead of hot water, so as to remove organic matter without coagulating the milk. Then wash thoroughly in hot water, using a good washing powder. The best washing powders possess considerable disinfecting action.[5] Strong alkalies should not be used. After washing rinse thoroughly in clean hot water. If steam is available, as it always is in creameries, cans and pails should be turned over jet for a few moments. While a momentary exposure will not suffice to completely sterilize such a vessel, yet many bacteria are killed in even a short exposure, and the cans dry more thoroughly and quickly when heated by steam. Not only should the greatest care be paid to the condition of the cans and milk-pails, but all dippers, strainers, and other utensils that come in contact with the milk must be kept equally clean. Cloth strainers, unless attended to, are objectionable, for the fine mesh of the cloth retains so much moisture that they become a veritable hot-bed of bacterial life, unless they are daily boiled or steamed. The inability to thoroughly render vessels bacteria-free with the conveniences which are generally to be found on the farm has led in some cases to the custom of washing and sterilizing the milk cans at the factory.