First, let's give you a little background on what the two types of sparging are.
How to Fly Sparge
Fly sparging is the process of using a sparge arm, or any device that allows the water to sprinkle over the grains in the mash tun. A sparge arm is used as it helps prevent channeling of the water in the grain bed. Channeling should be avoided if you want to achieve the highest extraction rate. During fly sparging the brewer's goal is to match the flow of the water going into the mash tun with the flow of the wort going into the brew kettle. You want the sparge (water flowing over the grains) to take about 60 – 90 minutes. This will allow for the best sugar extraction rate. Do not open your spigots all the way at any point during the sparge as this will result in liquid draining too quickly from the mash tun and you will end up with a very low starting gravity (S.G.).
You need to pay close attention to the flow rate when you fly sparge. Keep a constant eye on the amount of wort being collected and adjust your flow rate if you are collecting too quickly or too slowly. Often during all grain brewing brewers will continuously monitor the runoff gravity using a hydrometer or refractometer and cut off the sparge when it has reached 1.010 to avoid leaching of tannins and other undesirable grain compounds.
How to Batch Sparge
Batch sparging is the same idea as fly sparging, but you do not need a sparge arm. With batch sparging, you completely drain the mash tun of liquid. Then you add more water to the mash tun and stir. We recommend replacing the lid and waiting 30 minutes before you drain the newly added water. After the 30 minutes, you drain the wort, and begin the boil process.
Batch sparging allows you to save time because you can open the spigots all the way. You do not have to monitor the flow rate as it does not matter. And, you do not have to take specific gravity readings as the gravity will not change throughout the process.
In the past, brewers stayed away from batch sparging because the efficiency rate was lower compared to fly sparging. Today's beer grains are modified specifically for brewing, and they do not appear to have the same issues as grains did years ago. If you find that your starting gravity is turning out a little lower then you expect, add a ½ pound to a pound of malted barley to your recipe.
Most of the all grain brewers at Midwest will use the batch sparging method because it is so much quicker than fly sparging, and you don't really lose any efficiency. Most of us started with fly sparging because making beer was just done that way for years. Frankly, it had to be done that way due to the poor conversion ratios you got with the grain available at the time. Now, the difference between the two methods is almost nothing. It might cost you an extra dollar to make an all grain batch using the batch sparging method, but it is unlikely that you will even need to use the extra grain.
Try the batch sparging method a few times and see what your results are. If your gravity numbers are low after a few tires, then go to fly sparging. The more you brew all grain, the higher your specific gravity numbers will be until you finally reach the maximum efficiency that you will get out of your all grain brewing system.For more information, check out the PDF Batch Sparging vs. Fly Sparging