Transepithelial electrical resistance (TEER, in ohms * cm²) in differentiating colonic epithelium derived from primary human colonoids with varying timing of butyrate in the luminal compartment. With Hanks Buffered Salt Solution in the luminal compartment (No SCFA), a high level of TEER is achieved by differentiation day 4. With HBSS with 10 mM butyrate (Butyrate-Early) in the luminal compartment from day 1 onward, TEER does not develop. Butyrate (10 mM) from day 3 onward (Butyrate-Late) does not impair the development of TEER. Points are offset on the x-axis from the ordinal days for visual clarity.