Most of the time, when people talk Brix in Garlic, they mean the clove juice, and a good rating is about 40, and the higher the better. The refractometer I have to use doesn't go that high, however, (I tried it by squishing the juice out of a rocambole clove once, and the line went all the way to the top, maxing it out). I looked for a way to get around that problem, and still use a field crop refractometer, so that I could still get in on the action with all my different varieties and strains of garlic. (A good refractometer costs $200, so far as I'm aware.)
If you've ever scaped a large plot of garlic, you'll know about that sap that drips like crazy out of the cut ends of a scape, and dries white and slightly crusty/itchy. It ruins running shoes and if you don't wash your scaping clothes right away, the smell can linger for weeks. Normally when you use a refractometer for field crops, you have to squish the leaves of soybeans and clover really hard to eek out a drop or two of juice so that you can test it. This scape juice pouring out just seems too easy, and you have to cut them off anyway! But why not, lets test the scape juice. I've done so for four years, on many different varieties to try and establish a baseline, or at least a range of what might be typical for garlic scape juice, and here are my results: Garlic Scape Brix testing at Golden Acres Farm