Gardeners have many tools at their disposal for measuring the quality of their produce, including soil tests that measure pH levels and nutrient content. Measuring Brix levels is another simple way to get information about the nutrient density of crops.
To test Brix levels, you use an inexpensive hand-held tool called a refractometer (pictured above) to send a beam of light through the juice from fruits, vegetables or their leaves. The amount of refraction (i.e., how much the light bends) tells you the ratio of water to dissolved solids, such as fructose and other sugars, proteins, and minerals inside. Refractometers can be purchased through retailers that sell home-brewing equipment and range in price from $16 to $250, though a standard refractometer is fairly inexpensive, at $30.
The results from the refractometer are compared to Brix charts to find out the crop’s rating (poor, average, good, excellent). Optimal Brix levels, measured as °Bx, vary from one crop to another. For example, asparagus is considered excellent with a Brix level of 8, but the Brix level must reach 22 for a pineapple to have an excellent rating. A higher Brix level indicates that the crop has higher sugar, mineral and protein content. In other words, the higher the Brix level, the better the produce tastes.
“Plants that are low Brix are mostly water,” explains Carl Pless Jr., an agricultural extension agent with the North Carolina Cooperative Extension in Concord, N.C.
German chemist Adolf Ferdinand Wenceslaus Brix pioneered the concept of measuring Brix levels in the 1800s. Although the concept has been around for centuries and is popular in winemaking and brewing beer, Pless says it’s “absolutely not” common for farmers to measure their Brix levels.
“A lot of the foods people are eating are on the low side of Brix, with values less than what would be considered poor,” he says. “You don’t find much [food] in the excellent category.”
The importance of measuring Brix extends beyond testing for harvest readiness, improved taste and increased nutrient density. According to Pless, high Brix levels also improve crop yield and reduce damage from insects and diseases. He likens farmers working to improve Brix readings to companies providing fair wages and good benefits to their workers.
“You need to take care of [the plants and the soil] to get good output,” he notes
Testing Crops’ Brix Levels
Using a refractometer to obtain a Brix reading is a simple process that can be done in the field. The Bionutrient Food Association offers these steps for using a refractometer to measure °Bx:
- Squeeze sap out of the leaves or fruit of a plant.
- Put two drops on the prism of the refractometer.
- Close the prism cover.
- Point the refractometer toward a light source.
- Focus the eyepiece.
- Read the measurement. (The Brix number is the measurement where the light fields intersect on the prism.)
- Compare the Brix measurement to the Brix chart to determine the score (poor, average, good, excellent).
Put Your Knowledge to Action
Once you know your Brix levels, you can “do the work to get your plants performing to their max,” explains Jana D. Bogs, MS, PhD, farm consultant and author of Beyond Organic: Growing for Maximum Nutrition (Dr. Jana Bogs, 2013). “It’s a nice monitoring tool in the field.”
But measuring °Bx is just part of an overall approach to better-tasting, more nutrient-dense fruits and vegetables. In fact, Bogs calls the readings, “helpful but not very specific.”
It’s essential to have an accurate picture of the factors influencing the readings, which means farmers must also test their soil for nutrients like nitrogen, calcium, phosphates and other trace minerals to determine what is impacting their Brix levels.
In addition to correcting nutrient imbalances in the soil to improve °Bx, farmers must also understand the impact of modern agriculture on optimal Brix levels.
“The charts are old and can be misleading,” Bogs explains. “Plants have been bred to put out a lot more sugar. What looked like a great reading [when the charts were developed] might not be accurate now.”
In fact, an excellent Brix reading now may mean that a plant has more sugar but is not necessarily more nutrient dense, according to Bogs.
Despite a few limitations, testing Brix levels remains a simple and inexpensive way to assess harvest readiness, taste and nutrient density—and determine whether changes to soil health are necessary to produce healthier, better-tasting crops.