Pete,
Another topic related to this discussion: Do you know about CAM photosynthesis? CAM stands for Crassulacean Acid Metabolism and is how cacti and sedum photosynthesize differently than most other plants. In order to conserve water, instead of respirating during the day, they fix their carbon dioxide at night so that their pores(stomata) can remain closed during the day, conserving water.
The nocturnally obtained CO2 is converted to — malic acid! which is stored in the cell's vacuoles until the morning. During the day when photosynthesis takes place, the organic acid product of nighttime CO2 uptake is then decarboxylated back into carbon dioxide and the energy in sunlight is used to convert the CO2 and water to sugar and oxygen.
An interesting side effect for our discussion is that CAM plants taste sour at night or early morning, and sweet or bitter during the day! So even the time of day has an effect on the taste.
The opening of the stomata is triggered by darkness and cool temperatures. I have read that cacti require temps below 70F or 20C to trigger the pores to open. This occurs naturally in deserts and high elevations where our cacti grow.
A problem occurs when trying to grow them in temperate regions. Indoors or during the summer, nighttime temps may not get low enough for the pores to open. The plant keeps growing but cannot photosynthesize so the new growth is brown and what we often refer to as "sunburn". It happens here in July and August, and also happens under lights indoors. The plant cannot make sugar for food and is literally starving. This is a problem for me every summer and I have to move all my cacti out of the greenhouse because it stays too warm in there at night.
In the fall when nighttime temps start to drop again, my "sunburned" cacti recover. I don't know what effect the summer stress has on mescaline production, but I assume it can't be good because it is commonly known that they get more potent during the winter when it is colder and darker and they are busy storing more malic acid rather than growing. My plants grow beautifully in the Spring after a long period of cold temps—plenty of malic acid has accumulated.
There is tons of info on CAM on the web but I thought you would be interested in this article:
Why Do Cacti Taste Bitter in the Afternoon?
Side project — I have been thinking of augmenting my soil with malic acid during the warmer months. I wonder if the plants can utilize it from the soil? Or perhaps a foliar spray at night?
And would a malic acid soil additive potentially increase potency?
Foliar Sprays of Citric Acid and Malic Acid Modify Growth