It is just prior to symptoms showing that one typically releases the most amounts of the virus into the environment
Symptomatic people are not the only way a virus is shed. The same is true in the case of Covid-19 infections.
An article, published by the World Economic Forum (WEF) and penned by Associate Prof of Biology Erin Bromage at the University of Massachusetts explains how infectious diseases spread.
At least 44% of all infections, and the majority of community-acquired transmissions, take place via people without any symptoms -- meaning, asymptomatic or pre-symptomatic people, according to the article.
A person can be shedding the virus into the environment for up to five days before symptoms begin showing.
Infectious people come in all ages, and they all shed different amounts of virus. The amount of virus released from an infected person changes over the course of infection and it is also different from person-to-person.
Viral load generally builds up to the point where the person is no longer asymptomatic and becomes symptomatic. So just prior to symptoms showing, one releases most of the virus into the environment.
However, data shows that just 20% of infected people are responsible for 99% of viral load that could potentially be released into the environment.