Too Much Straw and Trash in Your Combine's Grain Tank? Here's What to Actually Check

You pull up to the bin, open the hatch, and what's inside doesn't look like grain — it looks like a mix of grain, broken straw bits, chaff, and whatever else the field had to offer. Elevator hands frown, buyers knock points off your sample, and you're wondering where things went wrong.

Let's work through this properly.

1First — Figure Out WHAT Kind of Trash You're Looking At

Not all "impurities" mean the same thing. Before you touch a single lever, grab a sample from the tank and actually look at it.

• Light chaff and husk material— papery, lightweight stuff that floats. This is almost always a cleaning problem (fan or sieves).
• Broken straw pieces or short bits— suggests the threshing system is chewing up straw too aggressively, or the fan can't move it out.
• Whole unthreshed heads or cobs— the threshing isn't doing its job upstream, and the cleaning system is just catching what it can.
• Dirt, soil, and weed stems— usually a header/feeding issue, or you're picking up mud at the knife.
• Green material / weeds— you're racing through tough, weedy conditions and the cleaning shoe is overwhelmed.

2The Most Common Reasons Grain Comes Out Dirty

1. Fan Speed Is Too Low (Or Blocked): If it's not moving enough air, that light stuff just lands on top of the grain and rides down into the tank.
2. Sieves Are Opened Too Wide: Open them too much and everything — trash included — falls straight through into the grain tank.
3. You're Over-Threshing: Aggressive threshing pulverizes straw into tiny bits that are small enough to fall through the sieves.
4. Sieves Are Blocked: A quick brush-off at midday saves you hours of dirty grain.
5. You're Feeding the Combine Too Fast: Slow down first, let the machine catch up, and re-check.
6. The Crop Is Too Wet: Wait for the dew to burn off.
7. Worn or Damaged Parts: If you've adjusted everything and the sample still isn't right, check wear parts.

3A Step-by-Step Adjustment Process

Don't change five things at once. Here's the order I go in:

1. Stop and take a sample.
2. Check the sieves for blockage.
3. Slow the machine down.
4. Adjust fan speed first.
5. Adjust the upper sieve.
6. Check lower sieve.
7. Look at threshing.
8. Walk behind the combine.

There's always a trade-off. The goal isn't perfect — it's a sample that grades clean without throwing money on the ground. Most combines are designed to deliver grain around 2–3% impurity when set right; that's a reasonable target.