BMP testingBy-products of the agri-food industry

Grape seeds — BMP: 2 studies, weighted mean 214 m³ CH₄/t VS

Grape seeds are a by-product of winemaking and juice production; records from Italian studies show a woody material rich in fat and polyphenols.

CH₄ ≈ 52 % (estimate)

Published 8 July 2021Updated 29 October 20263 min readFeedstockData Editorial Team

Illustration: FeedstockData (AI, Google Gemini)

Weighted mean: 214m³ CH₄/t VS
Range: 175–253m³ CH₄/t VS
Records: 2studies
Publications: 2sources
Temperatures: —of the test

Methane in biogas

≈51–54% CH₄

Medium methane content · ≈ 5.2 kWh/m³ of biogas

estimate from the substrate type The collected studies contain no measurement. The interval follows from the approximate composition (carbohydrate-dominated (no protein or fat characteristics)) and the yields of compound groups according to FNR.

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 2 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 (214); 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

Download CSV

Source	BMP m³ CH₄/t VS	Temperature	Sample	Curve
Caramiello et al. (2013) DOI	175	—	Grape seeds	end point (model curve)
Carchesio et al. (2014) DOI	253	—	Grape seeds	end point (model curve)
Weighted mean	214	arithmetic mean 214, SD 55

Process properties

fibrous
slowly degrading
low in nitrogen
carbon-rich
high dry matter
contains inhibitors
seasonal
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 214.0 m³ CH₄/t VS (SD 55.2; 2 records, 2 sources).
Grape seeds: a dry, durable material, no risk of acidification - does not burden the VFA system (Hendriks and Zeeman 2009).

Drawbacks and risks

Polyphenols (tannins) at a high concentration inhibit hydrolytic enzymes (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 and alkalinity, balancing the high C/N of the material.^[1][2]
combines well
substrates: protein-rich — e.g. Food waste, Municipal sewage sludge (mixed), Poultry manure, Organic fraction of municipal solid waste, Grass clippings
The high C/N of the material balances protein substrates, limiting the ammonia risk.^[1][3]

Dosing

No source limits on the dose for this substrate.

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”).
Control floating crust and sediment: when solids are fed directly into the digester, the risk of their formation depends on the substrate (FNR 2010, Ch. 3).

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

Grape seeds are part of the pomace that arises after pressing the must (alongside skins and stalks). After separation they are sometimes used to produce grape seed oil and polyphenol extracts. The dataset contains several records from several Italian studies in which grape seeds were tested as a substrate for mono-digestion. Values were read from the abstracts of the publications. In Poland winemaking is developing, but there is little pomace and it is scattered across vineyards.

Properties relevant to digestion

The seed has a hard, woody coat with a high content of lignin and polyphenols (tannins, proanthocyanidins). Phenolic compounds at high concentration inhibit hydrolytic enzymes and microorganisms, and anaerobic bacteria degrade lignin very poorly. The seed contains oil, which after breakdown can yield methane, but its release requires breaking the coat. Size reduction and pretreatment therefore change the result significantly.

How to read the spread of results

The records come from Italy, but from different studies, and have no temperature given in the data read. Differences may result from the grape variety, the vinification process (seeds from red wines, after fermentation on the skins, differ from seeds from white wines), the share of residual pulp, size reduction and the inoculum. It should also be remembered that the seeds in these tests were not pretreated, and pretreatment significantly improves yield in studies by other authors.

In biogas plant practice

Grape seeds are usually more valuable as a raw material for extraction or oil production than as a biogas substrate. In the digester they increase the load of a poorly degradable structure, and their polyphenols can slow the process. When a biogas plant accepts grape pomace, the seeds arrive with it; dosing should then be gradual, and mixing adapted to suspensions of hard particles. The economic assessment should be based on a BMP test.

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 = 0.091 d⁻¹ was assumed (no kinetic data for the group – the median of all available rate constants k (93 values) was used).

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.