Why Does Hay Spoil?

Understanding Mold, Heat & How to Stop the Waste

You worked hard to grow a good crop. You timed your cutting, watched the weather, and put in the hours. But when you crack open that bale and it smells musty—or worse, looks like a biology experiment—you’re left wondering: What went wrong?

The answer is usually one word: moisture.
And the result is spoilage—something no hay grower wants to see.

Spoiled Hay Isn’t Just Ugly—It’s Costly

Spoilage doesn’t just affect how your hay looks and smells. It can:

• Lower the nutritional value of your crop

• Cause health issues in livestock

• Lead to wasted time, fuel, and money

• Damage your reputation as a hay supplier

Let’s break down exactly how and why hay spoils—so you can stop it before it starts.

What Causes Hay to Spoil?

1. Mold Growth

At moisture levels between 16% and 30%, mold, fungi, and yeasts start to multiply. These organisms feed on the sugars and nutrients in your hay, releasing heat as they grow.

You’ll often spot the signs:

• White, dusty layers (mycelium and spores)

• Musty odors

• Dry matter loss

• The risk of mycotoxins, which can harm livestock

2. Heat Damage

Even if you don’t see visible mold, heat can quietly destroy your hay’s quality.

• 16–22% Moisture → Hay can reach 115°F or more in storage

  • Causes discoloration and a loss of that clean, grassy smell

• 23–26% Moisture → Temps rise above 120°F

  • Leads to dark, caramelized hay and reduced feed value

• Over 27% Moisture → Hay may spike above 140°F

  • At this level, spontaneous combustion becomes a real danger

Spoilage Starts at the Baler—But So Can the Solution

The good news? You can prevent most spoilage with better moisture control and preservation—right from the moment you bale.

At Harvest Tec, we offer tools that help you protect your hay before mold or heat can take over.

💧On-Baler Moisture Sensors

Know the exact moisture of your hay as you bale. Make smart, safe decisions without the guesswork.

🛡 Baler’s Choice® Hay Preservative

Safely bale hay up to 30% moisture without spoilage. Baler’s Choice works by stopping microbial growth and preserving feed value—naturally, with no harmful chemicals. Learn more here. 

💨 Proper Storage Techniques

Pair our tech with best practices: airflow, stacking methods, and regular checks to keep your hay stable and safe.

Grow Smart. Bale Smart. Store Smart.

Spoilage may be common, but it’s far from unavoidable. With the right approach and the right tools, you can protect your hay—and your bottom line.

Explore more how-to articles and haymaking resources in our Haymaker Hub. It's your go-to spot for everything hay growers need to know.

Ready to Keep Spoilage Out of Your Operation?

Talk to your local Harvest Tec dealer or reach out to our team—we’re here to help you make hay that keeps its value, bale after bale.