Avoid Thin Kernels and Green Grain

Thin kernels and green grain are two of the biggest culprits behind rejected malt barley samples—and they often show up together. Saskatchewan growers know all too well how fast a promising crop can turn problematic when drought stress is followed by late rain.

Generally, maltsters are looking for at least 85% of the kernels to be plump, which means they don’t fit through a 6/64” sieve. Everything that falls through a 6/64″ sieve is considered thin (see image below from Malt Europe). Let’s break down why thin and green kernels happen, and what you can do about them.

Why Thin Kernels Happen

Barley plants under stress during grain fill—especially from drought or heat—will often abort later tillers or produce smaller, lighter kernels. Without enough moisture to fully develop the endosperm, you get thin grain with lower starch content and reduced plumpness. That spells trouble for malting and brewing.

Read more: Malt Barley Specs: Ensuring Marketability

Read more: Managing Late Tillers in Wheat and Barley

Key causes:

• Drought during grain fill
• Heat stress over 30°C
• Poor nutrient availability (especially nitrogen)
• Late tiller development triggered by mid-summer rains

Why Green Kernels Show Up

Late tillers triggered by rainfall in July or early August may not mature in sync with the main crop. These immature heads produce green kernels—grain that looks wet, soft, or distinctly pale compared to the rest of the sample.

Immature kernels:

• Don’t germinate well
• May contain higher moisture
• Contribute to heating in storage
• Hurt overall malt acceptance

Harvest Timing: The Balancing Act

When you’re dealing with a mix of mature and immature tillers, harvest timing becomes a balancing act. Harvest too early, and the main crop may not be fully mature. Wait too long, and green kernels may remain immature or become diseased.

Tips to Minimize Thin and Green Grain:

1. Manage fertility up front. Too much nitrogen late in the season can trigger new tillers. Stick to balanced, early-season applications to support even maturity.
2. Use plant growth regulators (PGRs) where appropriate. They can help reduce lodging and encourage uniform development.
3. Scout for late tillers. Especially after mid-summer rains. Monitor fields for uneven maturity. If possible, avoid areas of the field with late tillers to ensure top grade can be achieved for the uniform areas of the field.
4. Harvest at the optimal window. If most of your crop is mature but you see a few late tillers, it’s often better to prioritize protecting the majority of the crop. You can clean out the green kernels later if necessary.
5. Use combine settings to your advantage. Screen a sample to get an estimate of how many thins are in the crop. Adjust fan speeds to blow out light or thin kernels without losing good grain. Screening post-harvest can help salvage samples with some contamination. Watch: Combine Adjustments for Barley Kernel Size
6. Consider pre-cleaning before delivery. If your barley is borderline, screening can remove green or light kernels to improve overall specs.

In a year with uneven weather patterns and variable growth stages, these small decisions can protect your crop’s marketability. Maltsters are looking for consistent, plump, and uniform grain. Thin and green kernels stand out easily as red flags to malt buyers.