Farming News - FM BioEnergy case study: Silage additive boosts biogas at Vale Green

FM BioEnergy case study: Silage additive boosts biogas at Vale Green

A new silage additive from FM BioEnergy – developed specifically for use on UK grass – has doubled levels of beneficial acids following a successful trial at Vale Green Energy’s 1.5 MW Spring Hill AD plant, maximising biogas potential for the Evesham-based operator.


After nine days, both lactic and acetic acids – essential for good silage production – had significantly increased, while pH had been rapidly lowered to optimal levels. When the silage was analysed again, seven months after the initial treatment, beneficial acid levels were equally high while pH was still within the optimal range. The use of Silasil Energy SG has therefore avoided spoilage and minimised energy losses in the clamp long term, while preserving the biogas potential of the silage.

“Silasil Energy SG is very easy to apply and convenient to use and is flexible enough to work on wet or normal grass. The face of the clamp does not heat up when we expose it, meaning that the energy is staying where we want it to be – in the silage – rather than being lost to the atmosphere.”

Nick Reynolds, Feedstock Manager, Vale Green Energy.

The importance of good silage

Good silage production is essential to reduce energy losses in the clamp and preserve the biogas potential of AD feedstock. Lactic acid rapidly lowers the pH of silage, while acetic acid suppresses the growth of yeasts and moulds. Boosting the production of both lactic and acetic acids therefore enables silage to stabilise more quickly, reducing energy losses, improving storability and maximising biogas potential.

Nick Reynolds is responsible for producing feedstock for Vale Green Energy’s AD plants. With 12,000 tonnes of grass silage harvested from three cuts in 2023, he was keen to trial Silasil Energy SG, exclusively developed by FM BioEnergy’s German partner Schaumann BioEnergy in response to demand from UK AD operators.

Nick applied Silasil Energy SG to all Vale Green Energy’s 2023 grass crop and has been impressed with the results. “Not only is it easy to apply, but it works on both wet and dry grass, keeping the clamp face cool and ensuring the energy stays in the silage,” he states.

Analysing the benefits

Vale Green Energy worked with FM BioEnergy to quantify the benefits of the additive in a seven-month laboratory trial. Samples of their treated and untreated grass were taken by FM BioEnergy’s National Silage Specialist Andy Lee at the point of harvest in July 2023. The crop’s fermentation process was halted at three, six and nine days post-harvest by freezing the samples, which were then analysed at Schaumann’s laboratories in Germany. Further samples were taken from the clamp face in January 2024, approximately seven months after harvesting.

“The analysis showed that levels of lactic acid and acetic acid in the samples that had been treated with Silasil Energy SG had doubled after just three days compared to the untreated silage,” says Andy. “Nine days after harvesting, the lactic acid levels were more than double those of the untreated samples (2.95 compared to 1.35), while the pH was around 0.5 lower (3.94 compared to 4.41). Seven months later, acid levels were equally high and the pH remained stable. These figures show that, combined with good silage practice, Silasil Energy SG helps grass silage to stabilise more quickly, preserving its energy potential and improving storability.”

Effective on wet or dry grass

The variability of UK weather often results in large differences in crop dry matter from one season to the next. Previously, selecting the right silage additive was a challenge, with growers often stocking up on multiple additives to cover all eventualities.

The introduction of Silasil Energy SG means that this is no longer necessary: it works just as efficiently on wet and dry grass thanks to the presence of four bacterial strains, instead of the usual two. A combination of L. plantarum, L. buchneri, L. coryniformis and E. faecium preserve the biogas potential of grass in the clamp, regardless of whether the season has been wet, dry, mild or warm.

For Nick Reynolds, the trial has delivered the data to back up what he already knew from seeing the treated silage in his clamp – that by boosting lactic and acetic acids and rapidly lowering the pH, Silasil Energy SG is providing long-term protection to Vale Green Energy’s grass silage. “Our silage is free from moulds and yeasts, doesn’t heat up at the clamp face or during feed-out, and the energy is preserved for biogas production.”