Does higher pH speed up protein digestion? Stomach acid breaks down proteins. The rate changes at different acidity levels. You place albumin (a common protein) into test tubes at seven different pH levels. Every ten minutes you add a chemical dye to one tube from each group. After spinning the samples in a centrifuge, you check for color change. You also measure absorbance with a spectrophotometer at 580 nm. Digestion speeds up sharply as pH rises. At pH eight and above, the protein breaks down almost right away. Lower pH levels slow the process down.