I’ve been getting differences in Brix readings depending on how I extract liquid from my sample leaves. What would you consider the most accurate readings of leaf sap?
A: Brix is a useful tool when standards are known, but, according to Ohio State University Extension researchers, “At best, Brix values also appear to be indirect estimates of the general health of some crops and their potential sensory appeal to people. However, there is little scientific evidence to support the use of Brix values as anything more than an indication of the soluble solids content?and potential sweetness?of fruit and vegetable samples.” The full fact sheet, Using Brix as an Indicator of Vegetable Quality, is available at http://ohioline.osu.edu/hyg-fact/1000/pdf/1652.pdf.There is another school of thought that considers Brix readings to be indicative of much more, but if there are not standards for a given crop and a specific protocol for taking plant samples and readings, this becomes meaningless very quickly. For instance, foliar samples Brix readings can vary by the time of day, by the age of the leaves, by the season, by the means of expressing liquid, etc. If you establish your own protocols and are consistent with their applications, you might be able to determine something meaningful besides just the relative sweetness of the leaf juice or fruit juice. But if everything isn’t well controlled and standardized, you will not know what you’re really testing.