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Measuring Consumption in a Smarter Lunchroom: Tray Waste

Making healthy changes to the school lunchroom is a no-brainer, but how do you know if those changes are really making an impact?

Schools participating in USDA school meal programs are faced with regulations that dictate what foods kids can take as components of reimbursable meals. While these regulations require that the healthier foods be on the tray in order for the meal to be fully reimbursed, many students simply throw away unwanted components of the meal once they leave the lunch line. Thus the fruits and vegetables that kids toss are not providing them with any nutritional benefits; instead, they are adding to the cafeterias waste!

The Smarter Lunchrooms Movement has identified research proven methods that increase consumption of the healthy foods kids need. These strategies have been shown to increase consumption, decrease waste, improve the cafeteria’s bottom line, and improve student’s nutrition. By measuring tray waste, you can to determine whether the change is beneficial to your school and have evidence to share with interested stakeholders, including school administrators and community members.

Collecting tray waste data doesn’t have to be a huge, expensive and daunting task! Research from Cornell University shows that the Quarter-Waste Method is a reliable, quick, and easy way to accurately measure food waste. While literally weighing each student’s food waste with a digital scale is the most accurate method, it is time consuming and costly to do so. A viable alternative is the Quarter-Waste Method which is nearly as precise (90% reliability) as weighing. The method involves a visual estimation of food remaining on a student’s plate or tray. When students bring their tray to the waste basket, the researcher or data collector simply records whether ¼, half, ¾, or all of each food they can identify has been eaten. These percentages can then be used to calculate weight of food being wasted.  With this new method, measuring the impact of changes in your lunchroom can be done for no cost, with little hassle to staff or students, and can be done in only one school day.

Measuring tray waste can give insights into what foods kids are eating and what foods are being thrown away. In order for the healthy foods to give students nutritional benefits, they must first eat them! Before and after implementing changes in your lunchroom, collect tray waste for comparison. This empirical data can help you determine what healthy eating initiatives are effective and can also give school administrators and community members evidence of lunchroom successes!

Here are the easy steps to measure plate waste:

Materials: Scale, a long table, spreadsheet & pencil to record data

1. Set up a spreadsheet to collect data on. List every food item offered down the rows of the first column.  List tray number (1,2,3...200) in the next columns.  Each column will represent one tray or student and each row will represent the food item being measured.

2. Download Spreadsheet and Example:

3. Weigh Foods: Prior to the lunch period, weigh each food item being measured. To get the most accurate measurement, weigh at least three different servings and take the average (sum of the weight of three divided by 3). Determine the weight of each empty tray, plate, and/or bowl or other packaging (if there is any) that the food was weighed in. Subtract this number from the averaged total and the new total is the approximate weight of the item.  For items that are prepackaged, just record the weight that is given per serving on the package. Weighing servings not only helps you visualize a portion size but also can be useful in determining the nutritional value of consumed or wasted foods.

4. View Portion Sizes: All tray waste data collectors should familiarize themselves with what one portion of food looks like. This can be done can while taking the pre-weight. This way, they can more accurately estimate how much of the portion is remaining when the trays are discarded.

5. Set Up a Station: Prior to students’ arrival, set up a station at which trays will be collected. If possible, put the station near where students normally return their trays so that the change in the environment is less disorienting.

6. Collect and Record Data: Ask students to place trays on the table and as each tray comes in estimate how much food is left on the tray using the following Quarter Waste Method:

  • Enter a 0 for none wasted.
  • Enter a 1 for ¼ wasted.
  • Enter a 2 for ½ wasted.
  • Enter a 3 for ¾ wasted.
  • Enter a 4 for all wasted.
  • Record the observations on the spreadsheet provided.
  • If you can’t tell whether or not an item was on the tray, leave the corresponding space blank.
  • Only enter data for food wasted that you can identify.
  • Note that each numbered column represents a specific tray.

Once you have estimated and recorded each food item, you will be ready to analyze the data that you have collected!  

Analyzing Tray Waste Data Made Easy

The data that you collected can tell you the percentage of food being wasted before and after you implemented a change in your cafeteria. It will also tell you how many students are selecting food items. If food waste has decreased and students are selecting the healthful  foods that are being promoted, you know that your efforts have been successful! Sharing your successes is key to gaining support from the school community as well as from parents and district wide stakeholders! The best way to communicate your data is by presenting it in an easy to understand way. The following steps are designed to help you make your recorded data into simple, straightforward bar graphs that you can feature in school newsletters, at board meetings, or on the school website!

The first step is to organize your data by entering it into a Microsoft Excel spreadsheet. For help using the program, ask a high school business teacher or, better yet, a high school student!

1. Enter all of the data as it appears on your Tray Waste Data spreadsheet. Make one spreadsheet for the data collected before you implemented the change and one spreadsheet for after. Each column will represent one tray or student and each row will represent the food item being measured.

2. Next, average each row that represents a particular dish or food group (ie. entrée, fruit, vegetable, grain, milk). The average is calculated by adding all of the data in one row and dividing by the number of students that selected that item. Cells that are blank indicate that that student did not select the item being measured. Using the data below as an example, you would add  1+1+4+0=6 and then divide 6/4. The average of wasted green beans is 1.5.



3. Convert these averages to percentages by multiplying each calculated average by 25. For example if the average amount of green beans wasted is 1.5, when multiplied by 25 you find that an average of 37.5% of green beans are wasted.

Now you are ready to generate a graph that summarizes the findings. You can create one graph that shows the percentage of food being wasted. You will also want to share the percentage of students that select each item. For example if you are particularly concerned with vegetable intake, it is relevant to communicate the percentage of students selecting vegetables as well as the percentage of those vegetables that students throw out.

Percent Food Wasted

1. In a new Excel “workbook” create a chart that indicates the average percent food waste before and after implementation. For example:



2. To make this chart into a graph, simply select all of the cells in your chart (including titles) and click insert > chart > column. You will now see a simple readable graph!



Percent of Students Selecting Each Item

In a new Excel “workbook” create another chart that shows how many students are selecting each food item. To find this data return to your initial spreadsheet and count the students who selected each item and divide that number by the total number of students whose trays you measured. Remember that empty cells indicate that the student did not select that food item. Consider this example again:



According to this chart, 5 trays were measured and of those 5 trays 4 included green beans.

1. Once you have the number of total trays measured and the number of students that selected each item, calculate the percentage of students that select each item using this formula:   Total # Trays Measured/Trays that included food item X 100 = ______%

2. Plug these percentages into your new chart:


3. Follow the steps above to convert this chart into a graph:



Using Your Data and Graphs

Bar graphs created in Excel can be copied and pasted into other documents so that you can share your graphs easily! With your easy to read bar graphs you are ready to show off your results!

Beyond how much food is wasted or consumed, stakeholders may be interested in knowing about the nutritional value of the foods that students eat. Having the weight of each food item recorded in your spreadsheet makes it easy to look up nutritional values. Simply convert ounces to grams (if not already recorded in grams) and use the USDA National Nutrient Database for Standard Reference to find detailed nutrition information about the food item that you are analyzing. If you know how many calories, for example, are in one full serving of green beans and you know that 80% of green beans are being eaten you can easily calculate how many calories from green beans kids are eating by using this formula: calories in one serving X .8 = average calories eaten. This data can also be easily shared with a bar graph by following the instructions above.