Final answer:
Start monitoring the acid effect on potatoes after 3-4 hours of soaking at 37°C to observe changes caused by enzymes and microbes producing acids.
Step-by-step explanation:
You should start watching for the acid effect once potatoes have been soaking for 3-4 hours. At a specific temperature of 37°C, various organisms such as enzymes and microbes become more active and may produce acids as they metabolize substances within the potatoes. This process, referred to as incubation, primes the environment to observe the effect of acids on the potatoes. Soaking or incubating potatoes at this temperature is likely to be an experiment aimed at observing enzymatic activities and microbial growth which can affect the potatoes by altering their taste, texture, or appearance due to the production of acids.