Dark Pu-erh (also spelled Pu'er) tea is produced in China using Aspergillus foetidus var. acidus to ferment the tea leaves. Unlike Aspergillus niger, which it resembles, A. acidus does not contain mycotoxins ochratoxin A and fumonisins B2 and B4. The production is a lengthy process: e.g. a ripened Pu'er produced in early 2004 was pressed in the winter of 2004/2005, and appeared on the market between late 2005 and early 2006. The tea has in vitro antimicrobial properties against many microorganisms. Enhanced SEM shows two stomata (oval openings) in a darkened tea leaf and fragments of the leaf as well as fungal hyphae. The stoma in the upper half of the image is free but the stoma in the lower half of the image is full of debris. Image width: 75.3 micrometers. Magnification: 1330x if the image is printed 10 cm wide.