BMP testingFood and catering waste

Bread and bakery waste — BMP: 7 studies, weighted mean 370 m³ CH₄/t VS

Bread and bakery waste (wheat, rye, toast bread) is a starchy, readily fermentable substrate; the risk is rapid acidification at too high a dose.

CH₄ 48 %

Published 24 November 2020Updated 29 October 20263 min readFeedstockData Editorial Team

Illustration: FeedstockData (AI, Google Gemini)

Weighted mean: 370m³ CH₄/t VS
Range: 295–459m³ CH₄/t VS
Records: 7studies
Publications: 3sources
Temperatures: 35 °C, 38 °Cof the test

Methane in biogas

48.3% CH₄

Low methane content · ≈ 4.8 kWh/m³ of biogas

measured mean of 5 studies BMP, range 44.9–50.9 %; in a batch test the CH₄ share tends to be higher than in a plant.

How we calculate it and what the zones mean

Rating for biogas plants

not rated — editorial rating for biogas plants

Not rated: no dry matter or volatile solids in the data. We calculate the rating when the dry matter and volatile solids of the material are known.

Editorial rating per the methodology

Add to the co-digestion calculator CSV data

BMP curves from 7 studies

Weighted mean Individual records

Dashed lines are a model curve (first-order kinetics, B(t) = B₀·(1 − e^−kt)); the end point comes from the publication. All curves are model curves.

Cumulative methane production over the test [m³ CH₄/t VS]. The thick line is the weighted mean of all records (370); dots mark the end values given in the publications. Point at the chart to read values; click a legend item to hide or show a record.

Records and sources

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Source	BMP m³ CH₄/t VS	CH₄ in biogas % vol., measured	Temperature	Sample	Curve
Dubrovskis i Plume (2017) · 1 DOI	312	44.9 %	38 °C · mesophilic	Toaster bread (TB), damaged	end point (model curve)
Dubrovskis i Plume (2017) · 2 DOI	313	50.9 %	38 °C · mesophilic	Wheat flour coarse bread (WF), damaged	end point (model curve)
Dubrovskis i Plume (2017) · 3 DOI	335	50.6 %	38 °C · mesophilic	French bread (FB), damaged	end point (model curve)
Dubrovskis i Plume (2017) · 4 DOI	392	49.9 %	38 °C · mesophilic	Rye flour bread (RF), damaged	end point (model curve)
Dubrovskis i Plume (2017) · 5 DOI	427	45.4 %	38 °C · mesophilic	White bread with egg and milk (WB), damaged	end point (model curve)
Dubrovskis et al. (2018) DOI	459	—	38 °C · mesophilic	Rye bread Kursu waste	end point (model curve)
Kouas et al. (2017) DOI	295	—	35 °C · mesophilic	bread	end point (model curve)
Weighted mean	370	48.3 %	arithmetic mean 362, SD 64

Process properties

easily degradable
carbon-rich
saline
editorial classification

Low confidence: the description is based on general characteristics of the substrate group, not on studies of this material. Treat it as a hint to be verified.

Advantages

Methane potential in the Substraty.pl BMP dataset: weighted mean 369.9 m³ CH₄/t VS (SD 64.1; 7 records, 3 sources).
Starch and gluten protein; hydrolyses readily (Zhang et al. 2007).

Drawbacks and risks

A sharp rise in VFA at a high dose (Hagos et al. 2017).
Moulds and preservatives (e.g. propionate) in out-of-date bread may inhibit (Chen et al. 2008).

Co-digestion — what to combine it with, what to watch out for

combines well
substrates: high alkalinity (buffer) — e.g. Cattle manure, Pig slurry, Cattle slurry, Duck slurry, Rumen and digestive tract content
Slurry supplies N, alkalinity and trace elements.^[1][2]

Dosing

No source-based threshold; dose in portions.

Introduce gradually, starting with a small dose and monitoring the process (e.g. FOS/TAC, pH, gas composition).

Practical requirements

Shred: shredding increases the surface available for degradation and speeds it up, but does not necessarily raise the final gas yield (FNR 2010, Ch. 3 “Triturado”).

Sources of the process data

The co-digestion calculator will assess a specific mixture containing this substrate.

What it is and where it comes from

Bread is a product made of wheat, rye or mixed flour, and bakery waste includes unsold, damaged bread, failed bakes, dough remnants and crumbs. It arises in bakeries, shops, canteens and households. Bread waste is widespread, and in the food waste hierarchy priority goes to reducing losses and passing food on for consumption or feed. The dataset includes toast bread, wholemeal wheat bread, French bread, rye bread and white bread with added eggs and milk, as well as general bread waste.

Properties relevant to digestion

The main component is starch from flour, broken down by amylases into simple sugars, so degradation is rapid. Gluten protein, fat, sugar and salt are also present. Rye bread contains pentosans and more fibre, wholemeal bread more bran. Additives such as eggs and milk increase the protein and fat content. The main risk is acidification: a large dose of bread leads to a sudden formation of volatile acids and a drop in pH. Salt, preservatives (e.g. propionate) and moulds on out-of-date bread can affect microorganisms in larger amounts.

How to read the spread of results

Several records concern different kinds of bread, mostly from the studies of one team, so the spread partly reflects recipes: type of flour, share of bran, additives (eggs, milk, seeds, fat) and the degree of damage to the batch. The degree of size reduction, the substrate-to-inoculum ratio, the adaptation of the inoculum to starch, the temperature and the length of the test also matter. Records from one laboratory are more comparable with each other than with others, but they do not describe bread from other markets.

In biogas plant practice

Bread is a valuable co-substrate, which must be dosed evenly and at a small share, with monitoring of pH and volatile acids. Before feeding it should be size-reduced and packaging removed. Storing damp bread risks moulding, so storage should be short or after drying. Products with meat, dairy or eggs are subject to the rules on animal by-products, and food waste is waste within the meaning of the waste act, so acceptance requires a plant permit. Bread from bakeries may also be sent for feed.

Compared with other food wastes, bread is relatively uniform and dry, so it is easy to store after drying and to dose in constant amounts, which eases process control.

Methodology in brief

BMP is the amount of methane obtained from volatile solids (VS) in a batch test, given in m³ CH₄ per tonne of VS (numerically the same as NmL CH₄/g VS in the publications) and converted to normal conditions (0 °C, 101.325 kPa). The weighted mean gives each publication a total weight of 1, split equally between its results for the substrate — a paper testing twenty varieties does not outweigh a paper with a single sample. In inter-laboratory programmes the unit is the laboratory (total weight 1), and within it the weight of a test grows with the number of bottles (replicates). Results after pretreatment (e.g. thermal, chemical, enzymatic) are shown separately and are not included in the mean.

Solid lines are curves measured in the tests. Where a publication gives only the final result, we draw a first-order kinetic model, B(t) = B₀·(1 − e^−kt): only the end point comes from the publication, and the shape of the curve serves purely as visualisation — do not read the production on a particular day from it. For this substrate k = 0.232 d⁻¹ was assumed (median of rate constants k reported in the sources and/or fitted to the mean measured curves).

The statistics describe the spread of published results — a descriptive compilation, not a meta-analysis or a guarantee of plant yield.

Full methodology and correction policy

Bibliography

All sources of the site: bibliography.