So finer grain start at a lower strike temp?
No, milled grain size doesn't have any relationship to strike temp. RM-MN was just pointing out the effect of higher mash temps on time of conversion. I think you need to do some more reading on the mash process, but I'll give a quick high-level summary to eliminate some of the confusion you might have. Mind you, this is very general:
When planning a mash the first thing you want to determine, before you start, is at what temperature you want to mash.
Mashing at a higher temperature (for example, 156F) will result in a beer with a full body and some sweetness to it. Mashing at a low temperature (for example, 148F) will result in a lighter body with a higher ABV. A temp around 152F will be medium body and average ABV. You determine the target temp based on the style of the beer or your own particular desire.
The reason for the different results:
The act of mashing is converting starches to sugar. There are two primary enzymes in the grain that are activated by the heat that perform this process. In the higher temperature range, the enzyme Alpha Amylase is more active. It will break down starches in a way which creates multiple different types of sugar. Most of the sugars created by Alpha Amylase cannot be eaten by yeast (fermented) so they remain in the beer. This is why higher temps will result in a sweeter, fuller-bodied beer.
Beta Amylase is more active in the lower mash temps. It rips through the starches like a shark at a feeding frenzy, resulting in sugar which is very easily consumed by yeast. That all gets turned into alcohol (hopefully) and results in a less sweet higher ABV beer.
Let's say you want to shoot for the middle: 152F.
When you know how much grain you're using you can calculate how much mash water you need. Let's pretend your recipe calls for 3 pounds of grain. The general ratio of water to grain is 1.25 quarts of water per pound of grain. So in this case, 3.75 quarts, or just a hair under 1 gallon of water.
Next, you need to know the strike temperature of the water you're adding. This is going to be based on whatever temperature you decided on above. The final mash temp you're looking for (152F) is the result of:
Strike water temp (minus) heat lost to the grain itself (minus) heat lost to the vessel (minus) heat lost to stirring.
There are calculators online to help you make an estimate. Look at
this page. If you enter all the numbers above: 3 lbs grain, 3.75 water volume, 152F rest temp, the temperature of your dry grain before you start (I assumed 70F), it should come up with something like 165F. Meaning, if you want to mash at 152F for this recipe, you have to add about 1 gallon of 165F water to the grain.
Conversion is the term used to describe the process of the starch turning into sugar in the mash. The majority of conversion happens in the first 30 minutes. Everything is usually done in 60. Waiting 90 minutes is not an issue.
We haven't talked about sparging, which is the act of rinsing all of the sugars out of the grain when done mashing. But that's an entirely different topic. Additionally, carefully accounting for the pH level of the mash will help you be more successful, but don't worry about that for now-- concentrate on the basics first.
That's a general outline of how it works.
