Color is an important attribute of tomato quality. It is therefore precisely measured in raw tomatoes and tomato products to ensure consistent quality. 

The colorimetric grading scale and tomato grading standards help producers, tomato processors, and other stakeholders select the right tomatoes. Colorimetric scores quantify color to create the measurements needed to relate product quality to a grading scale. These scores and the grading process have been developed through extensive research and analysis to ensure color consistency and maturity.

Today's technological advancements in colorimetric measurement help offer higher standards for tomatoes and tomato-based products by providing fast and accurate testing of tomato color.

What Is Tomato Grading?

Tomato grading is a process for categorizing tomatoes by specific standards. The sizes and color of tomatoes are two factors considered in the grading process. Tomato grading helps set the price for tomatoes and can influence how they are stored, packaged, marketed, and shipped. 

The U.S. Department of Agriculture (USDA) lists the following tomato grades and standards:

  • U.S. No. 1. These tomatoes must be correctly formed and developed, smooth, clean, and mature. They must have uniform color and not be too soft. U.S. No. 1 tomatoes must also be free from damage, including sunscald, decay, and freezing.
  • U.S. No. 2. These tomatoes must be mature, clean, well developed, and uniform in color. They must not be overripe, but they can be slightly rough in texture. They must not be seriously damaged and must specifically show no signs of decay, sunscald, or freezing damage. 
  • U.S. Combination. These tomatoes consist of at least 60% of U.S. No. 1 tomatoes, with the remainder being U.S. No. 2 tomatoes.
  • U.S. No. 3. These tomatoes need to be clean, mature, and uniform in color. They should be well developed and not overripe, but they may have irregular shapes. They must not show any signs of freezing injury, decay, and serious sunscald damage or any other significant damage.

As part of tomato grading, the USDA considers color classification when evaluating the maturity of and thus grading of red-fleshed tomatoes at different tomato ripening stages. The USDA classifies tomatoes into the following colors:

  • Green. These tomatoes have a fully light green to dark green surface. 
  • Breakers. On no more than 10% of the surface of these tomatoes, green gives way to other colors, such as yellow, red, or pink.
  • Turning. On 10%-30% of the surface of these tomatoes, green gives way to red, pink, red, or a combination of these colors. 
  • Pink. On these tomatoes, 30%-60% of the surface is pink or red.
  • Light red. On these tomatoes, at least 60% of the surface is red or pink-red. No more than 90% of the tomato surface can be red.
  • Red. These tomatoes have red on more than 90% of their surface.

There is an objective colorimetric standard scoring system to determine product maturity and quality.

Colorimetric measurement and spectrophotometry are continually developing to meet the standards set forth by the USDA (United States Department of Agriculture). The USDA Processed Products Standards and Quality Certification Program uses a minimum standard grading chart to identify product value based on color measurement and consistencies.

Color is such a strong indicator of product quality that 30 of the 100 points awarded to the product are solely attributed to color alone. However, color measurement does present its challenges and can vary throughout the different stages of development and ripening process.

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How the Colorimetric Grading Scale Aids in Meeting Fresh Tomato Standards

Raw tomato color is evaluated using a standardized colorimetric grading scale. Like performing a pH test using indicator paper, this grading scale compares the color of tested tomatoes against the scale. During harvesting or processing, tomato samples are taken and evaluated by color to ensure they meet tomato industry standards. 

The colorimetric grading scale evaluates the maturity and grade of tomatoes at varied ripening stages. It can also help estimate the amount of the antioxidant lycopene in tomatoes. In general, the deeper red a tomato, the more lycopene it contains. 

Tomatoes are evaluated using a standard scale, so no matter where they are harvested, end customers get consistent product quality. If tomato paste manufacturers need red tomatoes for their product to ensure the right appearance of the tomato paste, a colorimetric grading scale ensures fresh tomatoes delivered to the processing plant from all over the country meet the required color for the final product. 

The standardized colorimetric grading scale can be used with the modern spectrophotometer for more accurate evaluation of both raw and processed tomatoes. Instead of relying on their own eyesight and experience, testers can use a spectrophotometer to accurately evaluate the exact color of a tomato or tomato product.

Technological Advancements in Colorimetric Measurement

There have been various changes in color measurement of tomato products over the years. Prior to 1972, all color acceptability ratings of raw tomato products were determined visually through the use of color discs to compare an acceptable minimum color standard.  The USDA has now developed a new standard of measurement, with color tiles replacing the colored disc as the standard measurement tool. These tiles can also be used to classify tomato color for grade development visually, but variations in individual color perception and the amount of time consumed by this process has now made this process nearly obsolete.

Tomato values are based on specific color scores and graded accordingly.

Today’s technology relies on spectrophotometers and colorimetric instrumentation to gather consistent and accurate results in an efficient manner. Most regulations require systems in which human judgment is minimized. Tools like spectrophotometers and colorimetric instrumentation help to eliminate the margin of human error and quantify results in accordance with U.S. standards for grade development in tomato products. Research and advancements continue to be made to correlate color measurement to lycopene content. Colorimetric instrumentation must continue to advance in order to meet needs and changes, as well as to accurately quantify results to meet the USDA and market demands.

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Tomato Color Measurement Methods From HunterLab

HunterLab has over 70 years in the industry, and we have been at the forefront of developing new technology for tomato processors and manufacturers. We have developed color measurement solutions that are recognized as best-in-class by the industry. 

Our handheld spectrophotometer, the MiniScan EZ 4500, and other solutions provide effective color measurement compatible with USDA classification systems. By providing you with accurate, fast information about tomato color, we help you meet industry standards for quality and allow you to deliver fresh, ripe tomatoes consistently. 

To discover more about how our solutions can be your partner in success, contact our color measurement expert.