The reason beer helps with spicy food at least temporarily is because it diverts the receptors temporarily.
However beer does not really help that much with spicy food and instead can actually make the burning sensation worse and not help it.
The alcohol content in beer is too low to dissolve the heat causing compound called capsaicin and the carbonation of the beer can also worsen the burning sensation.
The idea that beer can help with spicy food stems from the capsaicin dissolving in the alcohol, but the water in beer spreads the capsaicin and the alcohol itself is also an irritant and can increase the pain from the capsaicin.
When eating spicy food what you should not drink is water, coffee, other hot beverages, carbonated drinks like soda as these drinks can actually spread the heat causing capsaicin oil and make the burning sensation worse instead of neutralizing it.
Instead you should drink things like milk or eat yogurt, starchy foods like rice or bread or even drink acidic drinks like some lemonade.
Coffee not only can make the burning sensation worse when eating spicy foods but the coffee when consumed with the spicy foods actually tastes awful.
The reason why you should not drink water after eating spicy foods is because the water can make the spiciness worse.
The capsaicin which is the active compound in peppers is what is responsible for the spiciness, is not soluble in water.
Capsaicin is a hydrophobic molecule that hates water and binds to pain receptors in your mouth which causes the burning sensation from spicy foods.
When you drink water after eating spicy foods, it does not dissolve or neutralize the capsaicin and instead water can spread the capsaicin and make the spiciness worse.
Instead of drinking water after eating spicy foods to cool down the heat you should drink liquids that can dissolve the capsaicin.
Drinks and foods that can dissolve the capsaicin are cold drinks other than water, bread, yogurt and milk.
The starch in bread can absorb the capsaicin and reduce the burning sensation.
Yogurt, similar to milk contains fat and proteins that can also help with the spiciness.
And milk has fat and proteins which can bind to the capsaicin and neutralize the effect of the capsaicin.