Why does the amount of free HCl in gastric juice vary following the ingestion of a meal?

I think the basic idea is that proton pumps in your stomach increase the concentration of acidic H+ cations in response to food in the stomach. Eventually, the acidity will peak and the stomach will return to more basic concentrations. I think your body also produces bicarbonate (HCO3-) anions which help decrease the acidity. Consumption of carbonates and other basic foods also decreases the acidity.