Consider this a good to know, but not a need to know. Not knowing a lot about mash thickness won’t stop you from making a good beer. But learning about it can help you make a great one.
Different beer styles call for different mash thicknesses. On top of that there might be different stages of thickness (and temperature) for your mash. Again all style specific. But to boil it down, it comes to your liquor-to-grist ratio or volume of strike water in quarts divided by the mass of your grains in pounds. Not taking style into account at all, a ratio of 1.25qt/1 lb is a safe ratio that should give you a solid brew.
Thickness & Temperature
Thickness and temperature really control the characteristics of your wort. Alpha- and Beta-Amylase enzymes are your star players here. Alpha breaks up starch molecules which creates dextrines and sugars. Beta removes maltose molecules from the chains that Alpha creates. Together they give your wort what it needs to be fermentable.
Now here’s where temperature comes into play. The optimal temp range for Alpha to be most efficient is 149° to 158° F, Beta is 126° to 144° F.
Higher temp mashes produce less fermentable wort since the Beta isn’t as efficient as the Alpha. But on the flip side, thicker mashes help keep Beta activity up even in higher temperatures. Having that balance between temp and thickness can help you create a more fermentable wort.
You should record your mash thickness & temperature in your brewing notes. If your OG is off after the mash, adjusting your thickness, temp or both could help you increase your efficiency – giving you a more fermentable wort that would produce a beer closer to what your trying to create.