There are several reasons why an all-grain batch may turn out with a low efficiency; listed below are a few of the most common.
The water was not the correct temperature. When it comes to all grain brewing it is very important to make sure you are at the correct temperature during the mash. The ideal temperature is 152 °F for the proper conversion to take place. If you are too low, the starches will not convert into sugars. If you are too high, then the conversion process can stop. Yes, you do have about a 10° range that you can use, but the closer you are to the ideal temp, the better the efficiency will be. You need to be accurate throughout the mash process and not just at the beginning.
The mash time was too short. Some newer all grain brewers are not aware of how important time can be during certain stages of the process. You do not want to try and save time during the mash process because the grains will not have enough time to convert the starch into sugar, and you will end up with a low starting gravity. Follow the directions for the recipe as close as you can. If your recipe does not have a length of time for the mash use 60 minutes as your starting point. Most mash time frames will be between 60 – 90 minutes long.
The crack of the grain was too fine or not enough. What you want to look for in a crack is that the outer shell of the grain is cracked. You do not want something that looks like flour to make your beer with. That is too fine of a crack and the grain will not convert very well. If the entire grain is still whole, you might want to crack it a little more before use. Use a beer bottle or rolling pin to crack the grain if you feel that the grain is not cracked enough.
The sparge time was too short. This is especially true when using the fly sparge method. Do not cut time off during the sparging process. Keep in mind that fly sparging will take 60 to 90 minutes for most recipes, where batch sparging only needs about 30 minutes.
All grain brewing is a process, but it isn’t very difficult once you get the hang of it. Where most time is lost is waiting for the water to heat up to the correct temperature. Once you get a system down you will find that you can cut hours off the all grain brewing process. What might have taken you 8 hours the first time will usually lower to 6 hours or less over time. Stay patient, and enjoy a home brew (or two) when making your next masterpiece.