OK, lets look at the apples and lemons. First, our good old reams chart will tell us we want our apples to be around 13 to 18. So we know the apple will produce just sugar up until it reads over 10 (over simplification but will work for this example). At that point, provided it has minerals available it will start to complex minerals with those sugars. Now lemons, as we see on the chart, will go up to about 14 or so. Yes, lemons have the sugar, just not as much as the apples. So it takes less sugar to start a lemon complexing that it does for an apple. So what is the result, well a lemon at 10brix is going to be better than an apple at 10brix. I can’t locate any 10brix lemons but apples I can find between 10 to 13 all day. Once, I got an apple at 16 brix and it was good!
So just by looking at the chart we see that apples will have a slightly higher reading than lemons and we should factor this in when taking readings. I don’t like to look at it from the perspective of is this apple better that this lemon. I would say of all the lemons I’ve tested, most are 7 some were 5 and one was 10. So I know that anything above 7 would be on the better side of what is available to me. Plus I know that 14 would be the best of the best and it is possible, even if you can’t find them. Same for apples, 10 is normal 8 is very bad and 13 or higher is going to be hard to find. They will be good.
Now lets take a look at something like your pH 9.0 water. Since Brix is actually a measurement of “total dissolved solids” in a liquid, the pH is not what we are looking at. From what I do know, we need the sugar in the mix to refract the light and the other solids in the liquid will alter the refraction of the sugar. Bottom line, no sugar no reading. Regardless of what might be in the liquid. In other words we are looking at the amount of minerals but not the pH of the liquid per say. A lemon that is 14brix will be loaded with alkalizing minerals. Further, it will leave an “alkaline ash” after digestion. However, if you test the pH of the lemon juice before eating it, it is an acid. What is it that ML always says: “things are not always as the first appear!”
I’ll rap this one up with ACV and other liquids that may or may not have some complexed sugars in them. ACV has had most of its sugars converted to alcohol then had that filtered out leaving the vinegar and the minerals ect in the remaining liquid. I’m assuming that process either leaves some sugar and or other substances in the liquid that will refract light. Add on top of that the minerals that will alter the refraction, and you can get a reading. Now we have nothing to base our reading off of. The best you can do is to log your data over time and use the numbers the best you can. If you were to test every brand of ACV you may find that one brand is a higher brix that others. This could be the determining factor on what brand you buy. In this way the refractometer could be useful for ACV and other such liquids.
Regarding your tea, do you get a reading at all? If no than you cant test it, but if you do, you could test it each time you make it and see if there are things you do differently each time that raises the brix.
Hope this helps and doesn’t confuse you more, let me know if you have more questions.