Keg King - Malt King - Geared 3 Roller Grain Mill - Adjusting Gap Size

We've assembled our grain mill, so the next step is to go ahead and adjust the rollers to the required gap size. Adjusting the gap size is important as it effects how the grain is crushed. A smaller gap will lead to a finer crush, which can help with conversion of starches to sugar, but can cause issues with recirculation or sparging, since the water is not able to flow through the grain bed as easily. Conversely, a larger gap will give a coarser crush, which can aid in water flow through the grain bed, but can lead to decreased conversion of starches to sugar (ie. efficiency). Finding the sweet spot for your brewing system is key, and like most things, setting the gap size is pretty easy once you know how to do it. The provided instructions with the grain mill certainly lack the kind of detail you need to do it properly. Read on for some detailed steps on how we did it.

Before we begin, there's a couple of things we should point out. First of all, you will obviously need to know what gap size you wish to set your mill to. What gap size to use is dependent on so many factors - brewing system and malt variety or even malt manufacturer are just a few that can impact on your desired crush/gap size.

We brew exclusively on a BrewZilla 3.1.1, so we checked with someone much more experienced than us, Gavin, from The Homebrew Network on YouTube and he confirmed he uses 1.35mm for his crush size for most batches and grain types, so that will be our starting point.

We'd recommend using a feeler gauge to dial in the exact gap that you want - they're very cheap and take the guess work out. If you don't have one, lots of people recommend using the thickness of a standard credit card as a starting point.

First things first - the included instructions have only 2 steps on adjusting the mill, which are actually incorrect (it says to adjust the dials by moving them clockwise which you should only do for one, the other should be adjusted counter clockwise - we'll get to this later)

So, for the purpose of adjusting your mill, disregard the included instructions in this case.

Moving on, the first thing you'll need to do is remove the hopper. To do this, loosen the two bolts at the top of each side of the grain mill so the hop can slide out. You may need to use long nose pliers to grab the nut on the opposite side to stop it from spinning with the bolt. The mill can be left attached to the included board if you wish.

With the hopper removed, you now need to remove the four (4) screws that hold the face plate on to the main body. The face plate we're referring to is on the opposite side to where the two (2) large black adjustment locking screws are located.

Remove the face plate once the four (4) screws have been removed, which will expose the three (3) rollers.

On this particular grain mill, the only gap that can be adjusted is between the bottom roller and the upper roller closest to you (in the picture above) - also known as the drive roller since it has the drive shaft attached to it. The gap between the two (2) upper rollers cannot be changed.

Loosen the two (2) black screws on the back of the grain mill - this will allow us to begin adjusting. They only need to be loosened a couple of turns - not completely removed.

Looking at the front of the grain mill again - the next step is to turn the adjustment dials on each side of the mill so that the lower roller is at it's lowest point (closest to the mounting board). You'll notice as you turn the knobs, the lower roller will move in a circular motion at each end. The adjustment dial on the drive shaft side should be rotated clockwise, and the other side should be rotated counter clockwise (which will adjust the roller in the same direction for each side). Adjusting will change the gap between the lower roller and the upper drive roller (the one with the driveshaft connected).

The image below hopefully helps to illustrate the direction we're adjusting the lower roller.

Ensure your feeler gauges are set to the desired gap. Since we're setting a gap of 1.35mm, we're using a combination of 1.0mm, 0.25mm and 0.1mm (you bunch them together to give a combined gap of 1.35mm).

Insert the feeler gauge into the gap between the top drive roller and lower roller - on one of the sides. We would typically start on the side of the drive shaft but it doesn't really matter as both sides need to be done.

If you're starting on the drive shaft side - with the feeler gauge still in place, turn the adjustment dial clockwise which will move the lower roller up and towards you until it's tight against the feeler gauge and you can't move it any further.

Carefully slide out the feeler gauge, then insert it into the other (non-driveshaft) side. Leave it in place and turn the adjustment dial counter clockwise. This will move the lower roller in the same direction as we did for the other side - up and towards you until its tight against the feeler gauge.

It's important the dials are moved in this manner to ensure the bottom roller is aligned correctly. If you move both dials the same direction (eg. clockwise), then one side of the roller will move up and towards you, and the other side will move up and away from you, resulting in a crooked roller, and an inconsistent grain crush.

Slide out the feeler gauge, then repeat the process to double check. Re-tighten the black adjustment knob on each side to lock the bottom roller in place.

A good indication that you've done it correctly is if the dials are at the same position on each side. For us, adjusting to a gap of 1.35mm had the dial on both sides at the position shown below - between the 2.41mm and 2.16mm settings.

Based off this we think it's fair to say the numbers around the adjustment dials are not accurate or reliable so should not be used unless it's purely as a reference point, and not to actually determine your gap size.

You can mark the adjustment setting with a marker or centre punch if you wish - we're going to wait until we've done a few batches with some different crush sizes before making any permanent markings.

The mill has now been adjusted and set to your desired gap size. Reinstall the face plate and hopper and you're all set!

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