The short answer
A steel keg starts with a mortgage. Producing six kilograms of chrome-nickel steel costs considerably more energy and greenhouse gas than a one-kilogram plastic container. The keg pays that mortgage off by running again and again – and from a certain cycle onwards it comes out better than the single-use container.
We found two studies on where that point lies. They arrive at different figures, and that is not a contradiction but a question of assumptions.
Depending on the study, the break-even point against single-use plastic lies between 15 and 38 cycles. Against plastic containers with a closed recycling loop it moves to around 60.
The documented service life of a reusable keg is 60 to 180 cycles or 10 to 30 years.
So the steel keg wins – but only if it actually runs its cycles. A keg that ends up in the scrap container after twenty fillings has never repaid its manufacture on the stricter calculation.
Study 1: 15 to 20 cycles
The Swiss life cycle assessment group treeze Ltd. (Uster) calculated a steel keg against two single-use plastic containers in 2013 on behalf of Franke Blefa GmbH. The authors are Franziska Wyss and Rolf Frischknecht; the latter is one of the better-known names in European life cycle assessment.
| Parameter | Steel keg | Plastic 1 | Plastic 2 |
|---|---|---|---|
| Capacity | 19.8 l (1/6 bbl) | 20 l | 20 l |
| Empty weight | 6.00 kg | 1.05 kg | 1.00 kg |
| Material | 18/8 chrome steel, rubber | PET, aluminium, PE, rubber | cardboard, PET, various plastics |
| Country of manufacture | Germany | USA | Scandinavia |
| Transport to the brewery | 8,600 km | 2,500 km | 8,600 km |
| Distribution radius | 2 × 800 km | 800 km | 800 km |
| After use | cleaning, another cycle; 100 % steel recycling at end of life | 92 % residual waste, 8 % recycling | 92 % residual waste, 8 % recycling |
The result: the more often the steel keg runs, the smaller the share of manufacture in each individual filling. Washing and transport occur every time anyway and stay constant. From about 20 cycles onwards the steel keg is below the better of the two plastic containers in greenhouse gases, cumulative energy demand and water consumption; depending on the indicator, the break-even point is reached between 15 and 20 cycles.
What this study should not be asked to prove
The authors are unusually open here, and that belongs in the picture:
- It is expressly a simplified life cycle assessment that does not meet ISO 14040 and 14044 and was prepared for the client's internal use.
- The client is a manufacturer of steel kegs. That does not devalue the calculation, but it belongs on the record.
- The plastic containers were modelled with generic data sets for injection and blow moulding. The authors therefore write themselves that the greenhouse gas and water figures for the plastic kegs are not confirmed – and it is precisely these two processes that account for most of the total.
- The scenario is the US market, with 8,600 km of delivery from Germany. For a Saxon brewery with a radius of 60 km that says little.
- Filling is not included – neither the plant nor the cleaning media of the filling hall. It occurs in both systems, so it is missing from both balances.
The summary report is subject to copyright held by treeze Ltd.; reproduction of the text or the figure is not permitted without written consent. We therefore only give the results in our own words and name the source.
Study 2: 38 cycles – and 60 against the closed loop
In 2022 a peer-reviewed paper by Michael Martin, Sjoerd Herlaar, Aiden Jönsson and David Lazarevic appeared in Circular Economy and Sustainability under the title From Circular to Linear? Assessing the Life Cycle Environmental and Economic Sustainability of Steel and Plastic Beer Kegs. It calculates for the Swedish market and is cut quite differently.
Scope
Functional unit: the safe packaging of one litre of beer in a 30-litre keg. Considered from cradle to grave, including manufacture, transport, use and disposal.
Assumed service life of the steel keg: 80 uses at 5.5 cycles a year, so around 14 years.
Result
Manufacturing a plastic keg causes more than five times the greenhouse gases per litre of manufacturing a steel keg; in the closed loop still about four times.
Break-even point against the single-use plastic keg: 38 uses. Against both closed-loop scenarios: around 60 uses.
Economically the verdict went the same way, but more clearly than one would expect: for the brewery considered, the annual costs with steel kegs were around 932,000 SEK against around 1,090,000 SEK with single-use plastic – a difference of about two kronor per litre, around four in the closed-loop variants.
The authors' qualifications here as well
- The result depends heavily on the assumed service life of the steel keg. Manufacturers name over 100 uses or 30 years; the study calculates with 80.
- There were no reliable data for the recycling rates of the plastic kegs. The authors relied on media reports and conversations with breweries.
- The assumed distribution distance of 100 km could be too low for Sweden – and the distance is the most sensitive parameter in the whole calculation.
- Reusable plastic kegs were not included in the comparison.
Why 15 and 38 can both be right
Put the two figures side by side and you see no quarrel, but two different questions.
| treeze / Franke Blefa 2013 | Martin et al. 2022 | |
|---|---|---|
| Functional unit | one keg delivered empty | one litre of beer in the container |
| Keg capacity | 19,8 l | 30 l |
| Comparison product | two single-use containers | single-use and closed loop |
| Market | USA | Sweden |
| Electricity mix | US grid | Swedish grid, very low in CO₂ |
| Transport to the brewery | 8,600 km steel / 2,500 km plastic | predominantly European |
| Break-even point | 15–20 cycles | 38 and ~60 cycles |
| Peer-reviewed | no | yes |
| ISO 14040/44 | expressly not | journal standard |
| Client | keg manufacturer | research project |
Two points explain most of the difference. First, a 30-litre keg is heavier than a 19.8-litre keg but carries more beer – depending on whether you relate the figures to the container or to the litre, the ratio shifts. Second, a very clean electricity mix in the manufacture of the comparison product is the most effective lever against the reusable system: where plastic is produced with Swedish electricity and distributed over short distances, the steel keg has to work longer to build up its lead.
Anyone looking for a figure for Germany will find one in neither study. We have found no life cycle assessment that calculates European reusable steel kegs within the typical radius of a German regional operation. The honest answer to the question of the German break-even point is therefore: it probably lies between the two figures named, but that cannot be substantiated.
The second lever is distance
There is one finding in the Swedish study that speaks against the steel keg, and it deserves to stand here rather than be left out.
If the end customer is more than around 245 km from the brewery, the plastic container can become the better choice for greenhouse gases. For fossil resource consumption the break-even is at about 217 km. In the Swedish closed-loop scenario the threshold falls to around 150 km.
The reason is banal and unavoidable: six kilograms of empty weight travel along – and twice at that, out full and back empty. The single-use container travels once and weighs a sixth. Every extra kilometre penalises the reusable system twice.
That is no argument against the keg, but one for short distances. Reuse is a regional system. Anyone exporting draught beer over 800 km should not claim it is done for ecological reasons – the data do not support that.
Where does your fleet stand?
The two break-even points are only interesting if you know where your own kegs stand. Enter your figures – nothing more is calculated than cycles per year times years.
Cycle calculator
The marks on the scale are published values, not estimates.
The default setting – six fillings a year, ten years – matches the lower corner of the association figure of 10 to 30 years or 60 to 180 cycles. A keg that ends up there has both break-even points behind it, the strict one against the closed plastic loop only just.
What happens if the keg does not reach its cycles
All three break-even points – 15, 38, 60 – lie below the documented service life of 60 to 180 cycles. That sounds reassuring, and it is, as long as the keg covers the distance. But it does not do so automatically.
- The keg disappears. It stands in a cellar, in a workshop, in a yard. It is not broken, it is simply not in circulation – and every filling it does not do spreads its manufacturing load over fewer litres.
- The keg is scrapped although it still runs. Third-party kegs with no identifiable owner end up in the container as mixed scrap. The steel is recycled, the cycles are lost.
- The spear is not overhauled. The container is indestructible, the mechanism inside it is not. Miss the overhaul interval and you end up withdrawing an intact keg because of a worn valve.
Our own conclusion, expressly marked as such
Neither study models loss, missing stock or refurbishment. Both calculate with a keg that dutifully runs to the end of its assumed service life.
That is exactly where the most effective lever lies, in our view: a keg that is returned and kept running is not a little better ecologically than a new one, it is better by its entire manufacturing effort. No material optimisation and no recycled content can make up that amount.
In brief
The question “steel or plastic?” has no generally valid answer, only a site-dependent one. Within a sensible distribution radius and over a normal service life the reusable keg wins clearly according to both studies we found – from 38 cycles on the stricter one, from 15 on the milder one, with a documented service life of 60 to 180.
But the lead is not a material lead. It is driven on the road, cycle by cycle. A keg that does not come back wins nothing.