A Finnish company is reported in The Guardian as having developed a means of making a flour type food by passing electricity through water. The bubbles of hydrogen and carbon dioxide are used by microbes to produce the product. The food dispenser I envisage in my story may not be so far out after all.
Read the article: https://www.theguardian.com/environment/2019/jun/29/plan-to-sell-50m-meals-electricity-water-air-solar-foods