In the KEEKS-RP project, different forms of school catering in Rhineland-Palatinate were examined with regard to their greenhouse gas (GHG) emissions. Based on the completed federal project "KEEKS Climate and Energy Efficient Kitchens in Schools" (KEEKS), emissions were analysed in seven production and serving kitchens, which represent the following five catering systems:

  1. Fresh cuisine
  2. Cook & Chill
  3. Mixed kitchen with frozen (deep-freeze) insert
  4. Hot meals and
  5. Mixing kitchen with PK (plus-cooled) containers

The GHG emissions in [greenhouse gas emissions in kg CO2Eq] from the food ingredients used, from the energy consumption of the kitchen operation and from the transport costs within the respective catering form, i.e. from the production kitchen to the serving kitchen, were determined in each case. In addition, food waste that could not be further utilised was included and allocated a share of the emissions according to its percentage of the food served.

In comparison with previous experience from the predecessor project, it was determined where the study provided relevant information on the various forms of catering and where it represented "random" values for the respective facility studied due to the small number of project kitchens.

Participating schools and their catering options

The following schools and caterers were involved in the project:

  • A primary and secondary school plus (A) with its own fresh food kitchen
  • A secondary school (B) with a caterer's kitchen using the Cook & Chill method
  • An integrated comprehensive school (C)- Mixed kitchen with regeneration of tableware
  • One secondary school (D) and one primary school (E) - with fresh food provided by a service provider in the secondary school and hot meals in the primary school
  • A primary and all-day school in the form of an offer (F)- Mixed kitchen with frozen and fresh components by a caterer

Research methodology

The investigations in the school kitchens took place from the end of August to the beginning of September 2021. The GHG emissions of the menus served were determined during the project weeks. The menu composition, energy consumption, food waste and transport between production and serving kitchens were analysed. The individual analyses were as follows:

  • The menu composition for the project week was harmonised at the participating schools in order to make it comparable and to highlight differences in the catering systems. The ingredients were then assessed according to their GHG emissions from agriculture, transport and processing.
  • The energy consumption for electricity and natural gas for kitchen processes was determined for the individual kitchens and the resulting GHG emissions were allocated to the menu portions served.
  • The transports within the system, i.e. between production and serving kitchens (including cooling and warming), were also analysed for their GHG emissions and these were allocated to the menus.
  • No additional GHG emissions were calculated for food waste. However, the emissions from ingredients, kitchen processes and transport were allocated to the waste according to their proportion of the prepared food. This means that if, for example, 25 % of the food is thrown away, then the waste is also burdened with 25 % of the emissions. This is because all emissions from the production chain end up in the bin.

Exemplary results

As each type of catering was essentially only investigated using the example of a single kitchen, it is not possible to identify conspicuous results and differences.

  • be "accidental" due to the respective kitchen equipment, the size of the kitchen or its management
  • as well as "structurally" determined by the specifics of the respective catering form.

In order to differentiate between the two, we drew on experience from previous KEEKS projects with a large number of other kitchen analyses and consultations. When comparing the participating kitchens, it is initially noticeable that two of the school kitchens produce low GHG emissions overall (less than 750 g CO2Eq), while these are relatively high for the other three or four (around 1,500 g CO2Eq). However, the expected mid-range of 1.0 to 1.2 kg is not represented. 

The low consumption at School A is due to the essentially vegetarian diet and consistently low amounts of waste, which enables a relatively low use of food. School F also uses relatively little meat and no beef was used during the project week. In addition, the portions are relatively small, as it is a primary school and therefore only cooks for the first to fourth years, who generally eat less than older children and young people.

In this context, the high values for school E (primary school) may be due to the fact that its recipes were based on those of school D (secondary school). If the information is correct, this may also explain the relatively high amount of waste at School E. In the three kitchens with relatively high emissions - schools B, C and D - the proportion of animal products was relatively high in each case; i.e. even if vegetarian options were offered, the pupils were able to choose an alternative with meat and most of them did so. School C in particular, but also School B, have relatively high energy consumption in the kitchen. At School D, the GHG emissions from ingredients are conspicuously high. This is not only due to the type of ingredients, but also to the relatively large portions of food, including dessert, salad and - due to the coronavirus - bottled water. The following chart shows the proportion of emissions from ingredients and energy consumption in the participating kitchens:

Figure 7: GHG emissions of the ingredients and kitchen operation for one portion in the project week in [kg CO2Eq per menu]

keeks figure 7

Statements of the study on the catering forms

  1. There is no form of catering that would have relevant advantages or disadvantages in terms of the sum of GHG emissions.
  2. Transport within the system is not significant from a climate perspective. They accounted for only 1 % or 1.7 % of GHG emissions in the analysed facilities with hot and cook & chill catering. Even with acceptably longer distances, only little would be added here. The limit on the distance up to which food transport makes sense is limited more by the time it takes to keep the food warm and the driver. In large cities with high traffic volumes, congestion and high levels of particulate pollution, there may be other reasons for not transporting food. In particular, the fact that a serving kitchen often has to travel several times a day to provide hot meals and the short times required to keep them warm are a problem.
  3. In principle, the energy efficiency of kitchens increases with their size, i.e. the energy consumption per dish decreases. However, the energy-saving and therefore climate-protecting advantage of larger kitchens can be cancelled out or reversed. This occurs when kitchens are "over-equipped" with appliances, which is tempted by a more than adequate and actually welcome amount of space. Here, it is important to ensure that the equipment and staff training is adapted to the number of meals. 
  4. The greatest importance for climate protection is a climate-friendly, i.e. low-meat selection of ingredients, ideally without beef (burgers, spaghetti carbonara, chilli con carne). In terms of their importance for climate protection, this is followed by the minimisation of food waste and the use of efficient kitchen equipment, particularly for refrigeration and freezing, including energy-saving user behaviour. This is followed by the importance of the catering system. 

Nevertheless, there are some "key points" that are relevant for individual or several forms of catering and should be taken into account. These are

  1. In the - often "small" - fresh food kitchen, the energy consumption per dish is somewhat higher than is typical for "small" kitchens. Here, attention must be paid to energy consumption, i.e. efficient equipment and energy-conscious utilisation. In hot catering, increased quantities of waste are quickly produced because unused food can generally not be reused due to standing times and the lack of equipment in the serving kitchen. In the case of hot meals, particular attention must therefore be paid to minimising food waste, which is possible, for example, through repeated delivery, which is often necessary anyway to avoid long warming times. In order to reduce leftovers, the production kitchen must be informed before the second or possibly third delivery in order to reduce the amount of food to be delivered. Changing or optimising the ordering system can also help to avoid waste.
  2. The delivery of ingredients in PK containers can also lead to an increase in the amount of waste if no conscious attention is paid to waste avoidance during regeneration, e.g. by only using parts of the container. Staff must be trained accordingly.
  3. Separate systems such as cook-and-chill usually increase energy consumption by around 20 % during regeneration/heating due to the need for a "double kitchen". Added to this is the energy consumption for rapid cooling in the production kitchen, the "cold blowing". With this type of catering, particular attention must be paid to energy-efficient equipment.
  4. With cook-and-freeze, this additional consumption is "hidden" in the incoming goods due to previous production steps, which can lead to an increase in GHGs from the ingredients if there is a high proportion of frozen products.