Is 30 minutes like set in stone? The recipe i used in the past said 30 minutes. Is this ideal? Can I go longer? The recipe i have now doesnt say anything in this regard
30 minutes is not likely enough, unless you start with a very fine crush. Conversion of starch to sugar is a two step process. First starch must be gelatinized which saturates it with water. This is what happens when you cook rice for example. The second step is hydrolysis, where the bonds between glucose units in the starch react with water (catalyzed by the enzymes) chopping up the starch chains to create smaller molecules (dextrins and sugars.) Not all of the starch needs to be gelatinized before hydrolysis can take place, but hydrolysis cannot be completed until after complete gelatinization.
How long it takes a grit to completely gelatinize depends on the size of the grit (smaller grits gelatinize faster), the temperature of the mash (higher temps speed up gelatinization), and the nature of the starch (how easy it is to gelatinize.) Once gelatinization is complete, it takes only a few minutes for hydrolysis to complete (unless your enzyme concentration is very low, but most mashes have excess enzymes.)
When brewers have trouble with low conversion efficiency, it is most often because the mash time was too short at the chosen temperature(s) to completely gelatinize the size and nature of the grits in their crushed grain. Mashing longer, and/or adding higher temperature mash rests will usually lead to more complete gelatinization and conversion.
So, a legitimate answer to "how long should I mash?" is: mash until conversion is complete.
It is fairly easy to monitor the progress of gelatinization and conversion during the mash. As conversion progresses, the SG of the wort in the mash rises as the concentration of sugar increases. So, all you have to do is mash for a while, and then start periodically measuring the SG of the wort. A good schedule is to start SG measurements after mashing for 45 minutes, and then continue sampling every 15 minutes until the SG stops rising between samples. If you are using a very fine crush, you can start measuring sooner - say after 30 minutes. If you find you need longer mashes, you can wait longer before taking your fist sample.
The wort should be well homogenized prior to taking SG samples, or you can get erroneous measurements. Stirring or recirculation (if all of the wort periodically gets recirculated - something many AIO systems don't do) are effective for homogenizing the wort.
The easiest way to do quick SG samples is with a refractometer. They only require a few drops of wort, and the small samples cool quickly. It is important to minimize any water evaporation from the sample prior to measuring, as any evaporation will lead to erroneously high SG values. Pulling the sample with an eyedropper, pipette, syringe, etc. works well, as the small openings minimize any evaporation while cooling. You shouldn't try to measure hot samples if you want accurate results.
Brew on
