What is mashing...
Mashing is simply adding hot water to ground malted grain at temperatures where enzymes in the malt can break down starches and proteins. It really is that easy, but brewers have come up with different ways to conduct mashes.
In fly sparging, when the mash time is complete the brewer begins to slowly drain wort from the mash/lauter tun after conducting a vorlauf to attain clear runnings. Water is then run onto the top of the grainbed at the same rate that it is being drained in order to insure that the grain bed continues to 'float' in a volume of water. If the grain bed becomes exposed or the wort is drained too aggressively, there is a risk that it will become compacted, the result being a stuck sparge. The brewer must concern herself with monitoring proper ph, as too high a ph will lead to tannins being extracted from the grain husks. This method is more time consuming, taking an hour or more to run off the wort. Mash/lauter design is more important to be successful with this method, but it can attain high extraction efficiency.
Batch sparging is faster and easier than fly sparging, although the amount of sugar extracted from the grain will be a little less. Among homebrewers, it is a very common method of draining the mash. In this method, about half the sparge water is added to the grain, then allowed to sit and convert, after which it is drained into a kettle. At this time the remainder of the sparge water is added to the grains, stirred and then drained into the same kettle. The second addition of water serves to wash the grain of as much remaining sugar as possible. This champion of this method is homebrewer Denny Conn, who describes it clearly in detail here.
BIAB, Full Volume Mash
In the brew in a bag method, all of the brewing water is added with the grain at one time. This simplifies the process as there is no need to calculate how much water to add for each addition and what temperature each should be; it is done all at once. The kettle is filled with water, it is brought to the desired mash temperature, the brewing bag is placed inside the kettle and then grain is added into the bag and stirred. After mashing for sixty to ninety minutes, the bag is simply lifted up, allowed to drain and then removed.
Brewing In a Bag
Brewing In a Bag