Malting Overview


Malting has it's own language. Here's a list of common terms we'll be using throughout our documentation.

  • Maltster: You! A brewer brews beer. A maltster makes malt.
  • Chit: The first rootlet to emerge from the seed. It looks like a small white dot at the base of the seed.
  • Acrospire: The seed's first shoot. Maltsters track the malting process by measuring the acrospire. If the grain isn't kilned, the acrospire will turn into the first stalk and leaf.
  • Culm: The chit turns into rootlets over germination. After kilning, they become culms. Culms are brittle and brown, and need to be removed after malting.
  • Thins: Immature seeds, which won't germinate.
  • Chaff: Small bits of straw, husk, or other plant material.
  • D.O.: Dissolved Oxygen. The level of oxygen present in water. Colder water can hold more oxygen than warmer water.
  • Types of Grain


Malting is the process of sprouting and drying down seeds. It occurs in 3 main steps:

  • Steeping: Seeds are soaked in conditioned water, waking them up as if it’s spring.
  • Germinating: Seeds sprout over several days in a conditioned space, unlocking their energy reserves in preparation for growth.
  • Kilning: Before seeds use their newly available energy, they are carefully dried down to stop seed growth, while preserving enzymes.

In Depth

For an in depth explanation of the biochemical processes of malting, check out our article Inside the Seed.

Maltster / Acro tasks


Seeds are harvested with a combine, which roughly cleans the seed. It then goes through a seed cleaner, which gets rid of everything bigger or smaller than the correct seed. However, there are still thins and immature seeds mixed in, which are the same size as the seed, but won't germinate. To get rid of them, we wash the seed at the start of malting.

After weighing out the seed, it's placed in the conical. Select your recipe on the Acro, and select "Start Batch".

Acro will fill the conical with fresh water from the hose connection. It's going to fill more water than is used during steeping, about an extra 4 inches.

When Acro is done filling the wash water, grab your mash paddle, or use your arm, to create a whirlpool and stir up the grain. Thins, chaff, and other seed-sized things will float to the surface.

Grab your strainer and scoop out anything that's floating. Be careful to not dip your strainer too deep and grab viable seed. Also, don't use the strainer until the viable seed has settled back down.

Everything you take out during washing can be composted.

After you've whirlpooled and sieved off the floaties, select 'Drain Vessel' on Acro. The water will be drained, and then select 'wash grain' again to perform a second wash. This helps ensure you only have seeds remaining in the conical, and serves to wash any dust or dirt off of the seeds.

While draining, check the Inline Filter that runs between Acro and the vessel.

  1. Before doing so, ensure that the manual ball valve on that line has been closed, to ensure that water doesn't spill out the tubing.
  2. Twist the bottom of the Inline Filter to remove the filter from the filter body.
  3. Remove any residue caught in the filter and re-attach to filter to the filter body.
  4. Open the manual ball valve on that line to allow Acro to continue draining.

When washing is complete, Acro will begin the first steep. The correct volume of water for the quantity of grain entered in the recipe will be automatically filled.

Once the steep is filled, Acro will proceed with cooling and aerating the steep to set temperatures and DO levels.

Make sure the temperature sensor is inserted in the middle of the grain bed.

The primary task for the maltster during steeping is to track the moisture content. More info on this below.

When the steep duration set in the recipe is reached, Acro will automatically drain the steep.

** The drain tubing must be attached to the drain outlet before the steep starts, and the line must run either to a floor drain or an empty bucket. **

If the drain line runs to a bucket, the bucket must be emptied once the steep is completed.

Air Rests

Air rests aren't necessary in malting, but speed up the process. They allow seeds to respire, taking in oxygen and putting out CO2.

If your recipe includes air rests, Acro will open the valve at the bottom of the conical after the steep has been drained. Acro will blow air through the grain, dispersing CO2, and also cooling the grain if necessary.

Make sure the temperature sensor is inserted in the middle of the grain bed.

Keep the lid on the vessel in order to maintain a humid environment and prevent grain from drying out. It doesn't need to be clamped down.

Turn the grain around during the air rest to check on the consistency of the grain, to smell it, and to feel it.

Try to take an moisture reading at the beginning and end of an air rest.


When the final steep has been completed, it's time for germination to begin. Remove the valve from the bottom of the conical, and dump the grain out the bottom into a container. Insert the larger false bottom into the conical, and put the grain back on top of it. This is a good opportunity to mix the grain around thoroughly, and then put the temperature sensor back into it.

During germination, Acro will blow cold, humidified air through the grain bed, cooling the grain and dispersing CO2.

Turn the grain thoroughly with your hands once a day. Make sure to get down into the corners where the false bottom meets the conical walls.

Perform acrospire counts regularly.

Perform modification tests regularly.

Once the estimated germination length is approaching, perform acrospire counts and modification tests more regularly.


When the grain is properly modified, select 'Start Kiln' from Acro's menu.

You must be around Acro when kilning is occurring.

Don't turn the grain during kilning.

When kilning is completed, mix the grain around thoroughly inside the conical to deculm it, breaking the rootlets off.

Dump the grain out the bottom into your container by tilting the false bottom and pulling it out the top.


Place grain in a sieve and shake it around to remove the culms.


Store your fresh malt in an air tight container.

Moisture Content

The maltster's foundational tool is managing moisture content. We give seeds water through steeping, maintain it during germination, and take it away while kilning.

Moisture content directly relates to the degree of modification attained by the seed. A higher level of modification comes from a higher moisture content. A lower level of modification comes from a lower moisture content. For specific moisture contents of different malt types, please refer to the included book on Home Malting.

To track moisture content:

  • Set aside a small grain sample to track moisture and record the sample weight. The moisture content of your barley kernels is a major indicator of your progress during malting. It tells you when you’re done steeping and when your malt is finished. To track moisture, you’ll need to weigh your sample periodically and the weight change will tell you your new moisture content.

  • We put a 5 g sample in a standard tea ball. Other maltsters use mesh bags and larger samples. What’s important is that the sample is exposed to the same moisture and temperature as the rest of the grain, and that the sample kernels can not escape.

  • Throughout steeping, but especially near the end, you should be tracking your moisture content. We take readings when we transition between steeps and air rests.

  • To ensure accuracy, you need to get rid of any surface moisture from your grain. We actually empty our tea ball and pat the kernels dry with a dish towel until no more wet spots show up on the towel. Then we weigh the grain. When refilling the tea ball, we’re very careful not to leave any kernels behind, even broken kernels or other debris. If it went into the tea ball initially, it stays in the tea ball.

  • If you’re using a mesh bag, you may not need to take the grains out of the bag. Make sure you shake off most of the moisture then pat the bag/grains dry with a towel and weigh it.

  • Surprisingly, the moisture content usually rises during air rests. After draining the steep, there is a surface moisture on the grain which it takes up throughout an air rest. By the end of air rest, the grain’s surface is usually no longer wet to the touch. If you weighed your sample at the end of a steep, make sure you re-wet it so that it too can soak up surface moisture during air rest.

  • Calculate your current moisture content with your current sample weight. Here is the equation:

    • Current moisture % = 100 – (100 – starting moisture %) / (current weight / starting weight)
  • Let’s do an example together. You can assume the starting moisture content is 12%, as that is the safe level for long-term barley storage. The starting weight was 5 g and our current weight is 8 g.

    • Current moisture % = 100 – (100 – 12) / (8 / 5) = 45%
    • Perfect. We’re ready for germination!
Chit Counts

If you are doing air rests, the grain will start to ‘chit’ at some point during the steeping phase. The timing depends on your grain and your steeping times and temps, but we’ve seen the first chits as early as the end of the first air rest. It’s a good practice to do chit counts to track your grain’s progress and assess your grain quality.

Modern malting barleys ideally have a chit rate of 99%.

The chit is the first sign of the emerging rootlets. You will see something white poking out of one end of the kernel.

When we do a chit count, we check 50 kernels for this white protrusion, then multiply that number by 2 to get the chitting rate.

Acrospire Counts

There are a few ways to track the degree of modification. Big or small, the professionals don’t have better in-process control tests than you do in your basement. It’s all about feeling, looking, and smelling.

Track the growth of the acrospire as it grows along the edge of the grain. * Hold a kernel vertically between your thumbs, with the smooth side facing you. * Use your fingernails to split the outer layer open, exposing the acrospire just inside. This will take some practice to learn how to orient the kernel, and how much force to use. * Similar to counting the chitting rate, count the acrospire growth by analyzing 50 kernels. You can do this roughly once a day, but it is more important towards the end of germination. * Separate the kernels into categories based on the length of the acrospire in relation to the length of the grain. Double these results to get a percentage out of 100. * ¼x the length of the grain * ½x the length of the grain * ¾x the length of the grain * 1x the length of the grain * 1+x the length of the grain

  • When a majority of the kernels are between ¾ and 1x the length of the grain, it’s likely time to kiln. This takes some judgement on your own part. Don’t wait so long that there are many overgrown kernels past 1x the length, but do wait if you still have many kernels only at ½x the length.
Modification Tests

When you’re performing acrospire counts, roll the kernels between your fingers. There will be edges in the beginning preventing the kernel from rolling smoothly. The kernel will become squishier as modification progresses, and rolling will be smooth when modification is complete. Think of it as rolling a triangle between your fingers, which will gradually become a circle.

Another test to determine if modification is complete involves removing the husk from a kernel and smearing the white, starchy endosperm between your fingers. If the grain isn’t ready yet, you’ll experience a hard ball unwilling to smear. If the grain is ready, you’ll be able to fully smear the starch.

Grain Turning

Grain needs to be turned to detangle rootlets and prevent clumps from forming. In floor malting, it's necessary to disperse heat and CO2. Acro maintains temperature and CO2 levels independently of grain turning.

Your hands are your best tools in turning grain. It allows you to check on the smell, feel, look, and taste of the grain and build out your sensory analysis skills.

Make sure to dig down to the corners where the false bottom meets the conical walls. This is the most likely location for grain to clump.

Be gentle in turning the grain around - you don't want to be ripping off rootlets or acrospires. Damaged kernels can stop growing, resulting in unmodified malt. Damaged kernels are also the most likely source of mold growth.