This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
When the tank or barrel in which the beer fermented is not immediately used for the same purpose again, it must be well cleansed and dried, and thereupon be given a coat of a solution consisting of lime and water, which will prevent the growth and formation of fungi and germs of all kinds, so objectionable, highly detrimental, and retarding in the preparation of a second healthy beverage. When this barrel shall be put in use again a small quantity of hot water will quickly remove the lime from the same. Care must therefore be taken to insure that the lime is caustic or quick, a point that is frequently neglected. It is best to slack the lime fresh each time, immediately before using it, or, where this is not done, to keep at most three days' supply on hand; older slaked lime is of little use, for it has absorbed carbonic acid from the atmosphere and changed into carbonate of lime, or chalk. The chief end of the process is the destruction of acid-generating organisms which lodge in the wood pores, in order that they may not multiply too abundantly during the fermentation, and this can only be prevented by the use of fresh, caustic lime. It is also advisable to add to the freshly slaked lime a little soda which can easily be dissolved in hot water, say six ounces of crystalline soda to each three gallons of thick lime-milk. This is transformed by the caustic lime into caustic potash, and facilitates the removal of the lime wash even after the lapse of considerable time - an operation sometimes difficult where the caustic lime alone has been employed. .