There are several reasons why an all-grain batch may yield low efficiency:
The water temperature was incorrect.
When it comes to all-grain brewing, it is crucial to ensure that the mash is conducted at the correct temperature. The ideal temperature for proper conversion is 152 °F. If the temperature is too low, starches will not convert into sugars. On the other hand, if the temperature is too high, the conversion process can halt. Although there is a temperature range of approximately 10 degrees that can be used, being closer to the ideal temperature will result in better efficiency. Accuracy throughout the entire mash process is necessary, not just at the beginning.
The mash duration was too short.
Some inexperienced all-grain brewers may underestimate the importance of time during specific stages of the process. Trying to save time during the mash process can prevent sufficient conversion of starches into sugar, resulting in a low starting gravity. It is advisable to follow the recipe instructions closely. If the recipe does not specify a mash duration, use 60 minutes as a starting point. Most mash durations typically range from 60 to 90 minutes.
The grain crush was either too fine or insufficient.
When examining the crushed grains, it is important to ensure that the outer shell of the grain is cracked without turning it into flour-like consistency. A very fine crush will hinder proper conversion. If the grains remain intact, they might need further crushing before use. Using a beer bottle or rolling pin can help achieve the desired grain crush if you find it insufficient.
The sparge duration was too short.
This applies especially when employing the fly sparge method. Avoid cutting corners during the sparging process. Keep in mind that fly sparging typically takes 60 to 90 minutes for most recipes, whereas batch sparging only requires approximately 30 minutes.
All-grain brewing is a process, but it becomes less challenging with experience. The most time-consuming aspect is usually waiting for the water to reach the correct temperature. Once you establish a system, you will find that you can save several hours throughout the all-grain brewing process. What may have taken you 8 hours initially will typically reduce to 6 hours or less over time. Be patient and enjoy a homebrew (or two) while creating your next masterpiece.