Part of being an engineer is wanting as much data as possible to enter into spreadsheets that spawn into other spreadsheets. Another part is wanting to control as many variables as possible. The more you can control, the more repeatable your process is and the more you can understand what will happen when you change a variable. So after I made the jump to brewing all-grain it wasn’t long before I wanted my own mill.
After doing some research I bought a Barley Crusher. I’ve been very happy with the mill (especially once I stopped hand cranking), but now that I own this part of the process I also have to take ownership of the maintenance. The gap between the mill rollers can change over time. Maintaining the proper gap is crucial to consistent and efficient brewing.
The gap controls the crush of the grain. A small gap produces more grain flour which increases both the efficiency and the risk of a stuck sparge. A large gap leaves larger pieces of grain husk which helps with mash runoff but leaves more of the endosperm in tact which lowers efficiency. Therefore, brewers must find a balance to break the endosperm down enough while leaving the grain husk intact enough to efficiently lauter. A common mill gap setting for homebrewers is 0.038 inches. My system recirculates the mash and in order to make sure my mash doesn’t stick or channel I use a gap of 0.045 inches.
In order to measure and set a gap that small you will want to use a feeler gauge. A feeler gauge is made up of a number of metal blades of varying thickness. By isolating multiple blades you can create different thicknesses. To test my mill gap I put the 0.022 and 0.023 inch blades together. If you are unwilling to spend the $5 for a feeler gauge I’ve read you could use a credit card to get close to a 0.038 inch gap. However, keep in mind the mill rollers will scratch whatever you use to set the gap so use a the credit card that your significant other uses way too often.
When you are ready to set the gap it is very easy to adjust the position of the rollers for the Barley Crusher. First, loosen the two screws on the back of the mill with a phillips head screwdriver. It will only take about a quarter turn on these screws to free the rollers. After loosening the screws, just turn the knobs on either side of the mill to adjust each side of the roller gap.
Put the feeler gauge into the gap as you adjust the knobs. You want the feeler gauge to not be stuck in the mill, but also not be completely loose. The gauge should fit in the gap with some slight resistance, but you should not have to force it. Be sure to set the gap on each end of the rollers and the center. If you only set the gap on one side or in the middle, you could have an uneven gap with one side larger than the other. This would result in some grain passing through the mill relatively unscathed and some being pulverized to powder. The whole idea of setting the mill is to get a nice consistent crush.
Now your Barley Crusher is adjusted and set for your desired crush! My starting gravity issue disappeared on the brew day following my mill adjustment. It could have been complete coincidence, but it is one less thing I need to worry about. Setting the mill is another step in taking complete ownership of the brew day.