Denmark biogas production is set to rise sharply after Christmas, as fatty leftovers from the holiday table increase the methane yield from household food waste. Biogas Denmark (Biogas Danmark) estimates that biogas plants could produce up to 60% more green gas in January than in an average month, with the effect arriving after the holiday season because waste collection and processing takes time.
A January spike driven by duck, pork roast and gravy
The seasonal bump is tied to what Danes typically eat during Christmas: duck, pork roast (flæskesteg) and rich gravies. Compared with everyday meals, these dishes contain more fat, which generally increases the biogas yield when organic material is digested in biogas plants.
Biogas Denmark also expects up to 30% more food waste to reach Danish biogas facilities in January than in a typical month. The peak comes after Christmas rather than during the holidays because much of the waste is collected and delivered with a delay, especially from households and municipal systems.
Why fatty food waste produces more biogas
Biogas is produced through anaerobic digestion, a process in which microorganisms break down organic material in oxygen-free tanks. In simple terms, waste with a higher energy density can produce more methane. Fats tend to be particularly energy-rich compared with many carbohydrate-heavy leftovers.
However, the same characteristics that improve yield can also raise operational challenges. Biogas plants typically manage feedstock carefully to keep the digestion process stable, mixing household waste with other inputs such as manure, industrial organic residues and, in some cases, plant-based material.
Where the extra green gas ends up
The additional green gas from the Christmas period is expected to be used in several parts of the energy system:
- Residential heating, including households connected to gas boilers.
- Industry, where gas is used for process heat.
- System balancing, when wind and solar output is low.
Biogas Denmark argues that this role matters beyond climate policy. The organisation’s leadership has framed biogas as a tool for energy security, because gas stored in the system can help meet demand “when the sun is not shining and the wind is not blowing”.
Biomethane in Denmark’s gas grid and the 2030 target
Denmark is one of Europe’s most advanced markets for biogas upgrading. According to the Danish Energy Agency (Energistyrelsen), around 80% of Danish biogas is upgraded to biomethane and injected into the natural gas grid, displacing fossil gas. The agency says that in 2023, biomethane’s share in the Danish gas system reached almost 40%, and that Danish gas consumption is expected to be 100% green by 2030.
Biogas Denmark’s Biogas Outlook 2025 adds that in 2024, biogas accounted for around 45% of Denmark’s total gas consumption, when including both biomethane injected into the grid and biogas supplied directly from plants to end users.
This context helps explain why even a short-lived seasonal increase attracts attention: Denmark’s energy transition increasingly relies on multiple complementary sources, where renewable gas can provide flexibility that variable renewables do not always offer.
Limits of a seasonal boost and the broader debate
The Christmas effect is temporary, and it does not change the bigger constraints around biogas expansion. Denmark’s biogas sector has grown quickly over the last decade, largely supported by subsidy schemes introduced in 2012 and later closed to new applications in 2018. The Danish Energy Agency notes that new capacity is expected to rely more on tender-based support mechanisms and efficiency requirements.
There are also sustainability and climate questions that shape the policy debate:
- Feedstock choices: Denmark has tightened rules limiting energy crops in biogas production, and from 2025 the maximum share of energy crops is set to 4%, with the use of corn prohibited.
- Methane leakage: methane losses can undermine climate benefits, and Denmark introduced tighter rules in 2023 requiring monitoring programmes and regular independent leak inspections.
- Local impacts: the expansion of biogas plants can raise concerns about transport, odour and local environmental pressure, especially in areas with high livestock density.
What the Christmas leftovers story says about circular economy in Denmark
The seasonal rise in Danish biogas production is a small but telling example of how circular-economy systems work in practice: waste becomes a resource, and everyday consumption patterns can influence energy output. For Denmark, the immediate impact is limited to a few weeks of higher production and higher-quality feedstock.
But the broader significance is strategic. As Denmark and the EU push to reduce dependency on fossil gas, waste-to-energy and biomethane increasingly function as part of the infrastructure for resilience—especially in northern Europe, where winter demand for heat is high and renewable electricity output can fluctuate.
If the next decade delivers the planned expansion of renewable gas supply—alongside electrification, district heating and energy efficiency—Denmark’s post-Christmas biogas bump will remain a seasonal curiosity. Still, it underlines a key point of the Nordic energy transition: even leftovers can matter, when an energy system is designed to capture value from what would otherwise be thrown away.
