Another way to look at energy flows! Here is a Sankey diagram of US feed-to-food caloric flux. This is from a paper by Shepon et.al. titled ‘Energy and protein feed-to-food conversion efficiencies in the US and potential food security gains from dietary changes’ published October 2016 in Environmental Research Letters (Environ. Res. Lett. 11 (2016) 105002 – doi:10.1088/1748-9326/11/10/105002) under Creative Commons CC 3.0

Flows are in Pcal (Peta calories, 1012 kcal). Production figures are based on data from U.S. National Research Council and a “Mean American Diet” (MAD) with an average consumption of 2500 kcal per day is used. We can see energy in three feed classes being transformed into energy in edible animal products. The authors explain:

“On the right, parenthetical percentages are the food-out/feed-in caloric conversion efficiencies of individual livestock categories. (…) Overall, 1187 Pcal of feed are converted into 83 Pcal edible animal products, reflecting a weighted mean conversion efficiency of approximately 7%.”

In light of this, energy conversion efficiencies of 30-40% seem to be fantastic…

Check out the article for another Sankey diagram of protein flux.

Styria is the second largest state of Austria, in the south eastern part of the country. It is famous for its beautiful mountains, its wines and some decent yodelling 🙂

It is also home to green tech industries, in fact “Styria is home to more than 150 clean technology companies … [whose] revenue totals €2.7 billion. This equals to 8 percent of the Gross Regional Product (GRP), and is one of the highest concentrations of leading clean technology companies in Europe.” (Wikipedia)

The ‘Styrian Promise’ is a project aiming at the implementation of energetically and economically meaningful energy efficiency concepts in Styian production companies. Case studies from food, textiles, metals and other industries are presented on the project wiki.

Above is a Sankey diagram depicting the energy balance at Obersteirische Molkerei Knittelfeld (Upper-Styrian dairy in Knittelfeld). Flows are in MWh per year. The main energy requirement is steam from natural gas: Whey drying and steam for milk pre-heating are the largest consumers of process heat. Read more detail on the dairy production here.

A rather simple Sankey diagram. It can be found on p. 195 of a study on Food Waste in Germany by ISWA, Stuttgart University comissioned by the Federal Ministry of Food and Agrriculture (BMEL). Flows are in million tons per year (averaged for the five-year period 2003 to 2007).


The yellow streams represent food delivered to individual housholds (“Haushalte”) as well as to commercial (large scale) users (“Grossverbraucher”) such as restaurants. The orange arrows show food waste (10 mo. tons p.a.). Note that individual households have a higher reject rate.

In a presentation on “Low CO2 production in European food and beverage industry” the author Christoph Brunner from AEE – Institute for Sustainable Technologies (AEE INTEC) suggests process flow sheets and Sankey diagrams as tools used for energy efficiency analysis.

This Sankey diagram is used as an example for the creation of mass and energy balances and the visualization of the production process.

The diagram is from Austria and thefore in German. From translating some words I understand this is probably for a food/dairy industry. Flows are in MWh, but without a time span. Two steam generators (one run with natural gas, the other with petroleum) supply heat to different processes. The cooking chambers (“Kochkammern”) require most, followed by “Selch” (?) and heating of a “KSPW Tank”. Some heat is recovered from condensate.

Sankey diagrams can help understanding the energy flows of process systems and detect hotspots for optimization.

I am sure some of you know this situation: Stepping on the scales in the morning, still half asleep, just to find out you have gained a kilogram or so… but did I really eat that much yesterday?

Well, Ivan Muñoz from the Centre for Environmental Strategy (CES) at the University of Surrey approached this question from a more scientific perspective to create ‘A simple model to include human excretion and waste water treatment in Life Cycle Assessment of food products’. In LCA you are trying to explain all processes along the product life cycle in detail and, if possible, with a closed mass balance. When you look at the ‘use phase’ of a food product life cycle, where the food is being consumed it doesn’t disappear, it is just transformed in the human body.

The researcher and his group have determined a mass balance of 1 kg of boiled broccoli. It is visualized with two different Sankey diagrams.

One is a mass balance including water. The “first diagram reveals that human digestion is mainly concerned with water, from a mass point of view” (p. 13)

No units or absolute values are given, but one can see that wet matter (water) is the main constituent of the food ingested. It leaves the body as water through the lungs (exhalation), as urine and with faecal solids (light blue arrows). In fact, the human body could be considered a huge water extraction facility…

The other Sankey diagram just focuses on dry matter and oxygen, explicitly excluding the water in the broccoli from the mass balance.

Here we can observe that some 40% or so of the food dry matter are actually solids from non-biodegradable organics (fibres). See the arrow with the appropriate color 😉 . The remainder leaves the body as faecal liquids. In this Sankey diagram the human body rather is an emission source of greenhouse gases (GHG), solid waste and liquid waste.

Apparently in both diagrams no mass is maintained within the system…

The researchers also did an “endosomatic energy balance” and found that some 63,4% of the broccoli is “energy actually used in metabolism” while 36,6% of the energy is “energy in excretion products (lost energy)” (p. 15)

Now you might say ‘Who gives a … dime?”, but I found this to be a really fascinating topic. It is probably also the first Sankey diagram ever to be used to visualize human digestion.

I have talked about a cereals Sankey diagram by INRIA Grenoble a couple of weeks ago in this post.

Here are two more Sankey diagrams from the underlying article ‘Etude des flux de céréales à l’echelle locale: Exemples en Rhône-Alpes, en Isère et dans le SCOT de Grenoble’ by J. Courtonne, J. Alapetite, P. Longaretti, D. Dupré.

These are the mass flows for cereals production in France (2007/2008) in Mt (1000 tons)

Here is the same cereals process chain “translated” into a water footprint. Unit is million cubic metres of water consumed.

A very clear structure in both diagrams with three columns: grains production, transformation and final products. Choice of color corresponds to the topic.

A research group from INRIA Grenoble engineering school has set up a website for visualization of environmental data. Sankey diagrams are one available visualization option. The below is a sample provided on the website.

The Sankey diagram shows flows along the cereals production chain in France from the 2007/2008 harvesting campaign. Quantities are in 1000 tonnes.

Different grains are shown on the left: wheat (‘blé’), hard wheat (‘blé dur’), maize, barley (‘orge’) and others. Two large end nodes for unprocessed grain exports and use as animal feed (‘consommation animale’). There are further exports as intermediate and processed products. Only a comparatively small fraction is consumed by humans in France as bread, pasta, biscuits.

Could not detect use as energy crops, it is maybe hidden in the ‘industrial use’ flow. Anyway, an interesting application case for Sankey diagrams.

From a book ‘Environmental and climate analysis for the Norwegian agriculture and food sector and assessment of actions’ by John Hille, Christian Solli, Karen Refsgaard, Helge Berglann, Knut Krokann published on ResearchGate.

Download the full book on ResearchGate.

Not sure about the unit of flows.The unit of flows is kT CO2-eq./year (see comment by Christian Solli). The Sankey diagram shows embodied carbon in food and agricultural products and the overall carbon footprint caused by the demand of food in Norwegian households, and consequently along the supply chains in agriculture/fisheries sector. [Updated by phineas, May 06]

This is very similar to Jason Pearson’s Economy Maps for visualizing environmental impacts.