Following a poor harvest, for many agricultural AD operators, the biggest constraint on next year’s performance may already be sealed under plastic in the silage clamp.

After a challenging 2026 growing season across parts of the UK, much of the energy crop that will feed digesters over the coming year has already been harvested and stored. That means lower crop yields—and, in some cases, reduced feedstock quality—are now largely locked in. Operators therefore face a practical question: how do you maintain gas production from a smaller or lower-quality feedstock inventory without dramatically increasing operating costs?

For plants reliant on maize and other energy crops, a poor harvest can create a double challenge. Lower yields mean fewer tonnes available from the same acreage, while growing, harvesting, transporting and storing costs are spread across less material. If digestibility is also affected, operators can find themselves paying significantly more for every unit of methane produced.

The response doesn’t necessarily have to be buying more feedstock.

It may be time to think differently about how effectively we extract energy from the feedstocks we already have.

Getting More from Existing Feedstocks after Poor Harvests

At its heart, anaerobic digestion is a biological conversion process. Not all the organic energy entering a digester is converted into methane.

Many common feedstocks contain organic material that the digester biology simply cannot access efficiently. As a result, some of the energy entering the plant never makes it through to methane production.

This is particularly true for lignocellulosic materials, where valuable organic compounds are locked within plant structures that can be difficult for microbes to break down.

Feedstock pretreatment changes that.

By mechanically, biologically or thermally disrupting material before digestion, more of the organic content can become available to the microorganisms responsible for biogas production.

The objective is to improve the amount of methane generated from every tonne of feedstock purchased, harvested and transported.

There is strong scientific evidence supporting the principle. Peer-reviewed research involving ALPS Ecoscience and the University of Oxford investigated a range of pretreatment methods on commercially relevant maize and rye feedstocks. The study found that almost all pretreatments tested increased methane yield compared with untreated controls, although the response varied considerably by feedstock and treatment.

That final point is important.

Pretreatment is not a magic box that delivers the same percentage improvement for every material. The commercial question is whether the additional energy recovered is worth more than the energy and operating costs required to achieve it.

What This Means for Feedstock Pretreatment

This is one of the challenges that ALPS Ecoscience developed SMASH to address.

SMASH is designed to increase feedstock bioavailability before material enters the digestion process. Rather than accepting feedstock digestibility as fixed, pretreatment creates an opportunity to recover more of the energy already present in the material.

Independent studies into hydrodynamic cavitation and other pretreatment approaches support this wider principle. Full-scale research on agricultural feedstocks has reported increases in specific methane yield following mechanical pretreatment, while studies of lignocellulosic materials have demonstrated improved substrate accessibility and enhanced methane production.

For operators facing a difficult harvest, this changes the conversation.

Instead of asking:

“How many more tonnes of maize do I need?”

perhaps the better question is:

“How much methane can I economically extract from every tonne I have?”

That is ultimately the metric that matters.

If a plant can increase the proportion of feedstock converted into methane, it may be possible to offset of the impact of a reduction in available crop tonnage. Whether the same annual gas output can be maintained will depend on the scale of the harvest shortfall, feedstock quality, plant biology and the response to pretreatment.

The important point is that it should be measured, not assumed.

Looking Beyond Maize

A challenging maize year also creates an opportunity to reassess feedstock strategy more broadly.

Straw, grass, rye, agricultural residues, vegetable wastes, crop by-products and other locally available organic materials may all have a role to play in maintaining production.

The challenge is that many lower-cost materials are inherently more difficult to digest.

This is where feedstock diversification and pretreatment can become highly complementary.

A highly digestible but expensive feedstock may not deliver the lowest cost of methane production. Equally, a lower-cost feedstock with lower digestibility can become commercially attractive if pretreatment enables significantly more of its energy content to be recovered.

Research into hydrodynamic cavitation, for example, has demonstrated increased biomethane production from feedstocks including grass silage, wheat straw and agricultural residues.

The opportunity therefore becomes:

Lower-cost feedstock + effective pretreatment = lower-cost biomethane production

For operators under pressure from rising feedstock costs, that equation is becoming increasingly relevant.

Focus on £/MWh, Not £/Tonne

Perhaps the biggest lesson from difficult growing seasons is that feedstock purchasing should not be judged solely on cost per tonne.

Tonnes are not what AD plants sell.

We sell energy.

The more useful calculation is therefore:

[Feedstock cost
+ transport and handling
+ pretreatment cost
+ plant operating cost]

divided by

[recoverable methane energy]

equals

[true £/MWh of biomethane produced]

A £45/t feedstock can ultimately be more expensive than a £60/t feedstock if substantially more material is required to produce the same methane output.

Likewise, a material traditionally viewed as a poor AD feedstock may become commercially attractive if technology enables significantly more of its organic content to be converted into usable energy.

The question is not what a tonne costs.

The question is what a megawatt-hour costs.

A Different Response to a Difficult Harvest

No pretreatment technology can create energy that does not already exist within a feedstock.

What it can do is help recover a greater proportion of the energy that is already there.

That distinction becomes increasingly important during years when crop availability, quality and pricing come under pressure.

The response to a poor harvest should not automatically be:

“Buy more expensive maize.”

There are at least three other questions worth asking:

1. Can we extract more methane from the feedstock we already have?
2. Can pretreatment make alternative, lower-cost feedstocks commercially viable?
3. Can we redesign our feedstock mix around the lowest cost per unit of renewable energy rather than the lowest cost per tonne?

For many plants, the answer may involve a combination of all three.

The most resilient AD plants are unlikely to be those with access to the cheapest maize. They will be the plants that can extract the greatest value from whatever feedstocks are available.

In years when crop availability, quality and price become less predictable, technologies that improve feedstock flexibility may prove every bit as valuable as technologies that increase methane yield.

That is where the real opportunity lies: not simply producing more gas, but building a more resilient, adaptable and economically efficient biogas operation.