Once they are eligible for harvest based on accepted criteria, many vegetables are picked as labor, weather, market and other conditions dictate.
Many criteria are used to determine if a crop is eligible for harvest and marketing. Size, shape, color, firmness and weight are among the most commonly used — they are mostly objective, can be assessed quickly and reliably and they influence “eye appeal” during marketing and distribution. Many growers tend to use one or more of these objective criteria alone to determine if a crop is ready to harvest and market. 
That said, other, more subjective criteria such as flavor and nutrient content may also be useful. Of these, components of flavor may be the most easily, inexpensively and reliably evaluated on farms using °Brix values.
°Brix is a unit used to express the level of soluble solids in a solution. Sugars, pectins, organic acids, and amino acids are the most prevalent soluble solids in the marketable unit of most vegetable crops. Sugars tend to be the most abundant soluble solid in these units; therefore, sugars tend to contribute most significantly to vegetable °Brix values.
The most abundant sugar in many crops is sucrose. It is in the class of sugars that can contribute to the level of sweetness that is perceived when a product is eaten. MANY compounds contribute to flavor so there is NO guarantee that higher °Brix readings will result in the product tasting 
sweeter. In fact, some Brassica crops tend to have much higher °Brix levels than other sweeter-tasting vegetables (the sweetness based on sugar content can be masked by other stronger-tasting compounds in the vegetable). Still, °Brix values have become a key bit of information for enterprising growers interested in knowing more about their crop: for example, how varieties and soil and crop management influence soluble solids levels in their crop and how sweet their crop may taste to consumers.
In fact, when obtained and applied correctly, °Brix values can aid in variety selection, harvest scheduling, and other aspects of crop production (e.g., irrigation, fertility, and post-harvest management). An overview of the use of °Brix is given in The Ohio State University Fact Sheet HYG-1650-12, Using °Brix as an Indicator of Vegetable Quality by Kleinhenz and Bumgarner. Other Fact Sheets in the same series provide an overview of the use of °Brix and describe how to collect and use °Brix values in specific crops. Two videos are also available as training tools: What is Brix anyway? and How to Take Brix Measurements. Reference values are available in government and scientific reports and other documents. These resources are a straightforward and comprehensive introduction to measuring and using °Brix values.
In Spring-Fall 2011, we cooperated with eleven growers throughout Ohio in measuring °Brix in twenty-four different crops. The numbers were surprising. °Brix values varied widely within crops (across farms and harvests), suggesting that this aspect of crop quality differs significantly for individual crops farm to farm and picking to picking. Based on the results of that and follow-up tests, we are confident that, with sufficient calibration, growers who routinely measure °Brix are more prepared to select varieties and production practices that result in crops with higher °Brix values.