I was reading that the best time to take a brix reading is mid-day around noon. I can't remember where I read that info, but it has something to do with the way the plant produces sugars. I will try to find the article.
I also was reading that when you take a sample, the best and most accurate way to get a reading is to use the juice from the entire leaf. By just squeezing the leaf without grinding it up, it only will release the "newer" juices, but leave in the other's is the way I understood it. So when I take my readings, I am using pliers...way before I take a sample of the juice, I ball up the leaf and crush it a few times, each time pulling the leaf material out, balling it up and repeating the process. When I get a leaf that looks all chewed up, I know that the sample will have a better accuracy in reading the entire leaf's brix... I got that from a youtube video.
As far as where to sample on the plant... I haven't really found the right answer yet... all I was reading was when pulling samples, to make sure to always take from the same area or type of leaf growth.. to keep the best consistency...
On another note...:
I also read an article last night that was saying that plant leaves pull nutrients from foliar sprays in different timeframes, so even though a brix reading can change within 2-24 hours.... some foliar nutrients may take days if not weeks to fully be utilized by the plant leaves... to this makes me wonder when is the exact best time to take readings.... Another thing I am getting conflicting info on is how often to foliar spray.... I have read 3-4 times for the entire growing cycle...some are doing it weekly, some are doing it daily... but I don't know what is the best for the high brix focus...any thoughts..?
I hope you don't mind me posting all my findings about high brix here...it seems this is a great place to get all the High brix info, all in one place...
Rates of Nutrients Absorption into Plant Tissue (9, 10, 18, 27)
Nutrient Time for 50% Absorption
Nitrogen (as urea) 1/2 - 2 hours
Phosphorus 5 - 10 days
Potassium 10 - 24 hours
Calcium 1 - 2 days
Magnesium 2 - 5 hours
Sulfur 8 days
Zinc 1 - 2 days
Manganese 1 - 2 days
Iron 10 - 20 days
Molybdenum 10 - 20 days
Meteorological Conditions Favoring Foliar Applications
Time of Day: late evening; after 6:00 p.m.
early morning; before 9:00 a.m.
Temperature: 65-85½ F; 70½ ideal
Humidity: greater than 70% relative humidity
Temperature/Humidity Index: 140-160
Wind Speed: less than 5 mph
pulled from PDF...very good info for helping us get the right foliar applications...