You cannot safely or reliably make pure kojic acid at home
Kojic acid is typically produced by industrial fermentation of fungi such as Aspergillus oryzae
Home production is not recommended because it requires controlled microbiology, purification, and chemical handling
If you want kojic acid for skincare, buy a reputable cosmetic-grade product instead
If you want a DIY brightening option, use safer ingredients like niacinamide, vitamin C, or licorice extract
Patch test any skincare product before use
Stop use if irritation occurs