How to Appropriately Check Mash pH

I've purchased a handheld ph meter and wanted to make sure I was checking the mash ph correctly. I believe I read somewhere I am to wait 30 minutes into the mash, then let the sample of the wort cool to room temperature and then check ph. This is the procedure I have been using.

Specifically, I wanted to know if the amount grain in the sample glass would effect the ph level in any way, as the grain and and wort are still in contact with one other (in the sample glass) while cooling, possibly changing the pH. Currently, I am using EZ Water to estimate my ph levels and have been off by 3 tenths (under 4.9) and am looking for some reasons why. Thanks.

-I calibrate the pH meter each time I use it with the 4 and 7

Thanks again!

I just edited the pH Calibration Sticky to include the steps for checking mash pH. You seem to be doing every thing right. If you are following the instructions for measurement and calibration in the sticky and if your meter passes the calibration stability test set out there then the problem is not with your meter. Inexpensive meters, however, are often not stable and instability of a couple of 10ths is not that uncommon. OTOH the spreadsheets use simplified models of the acid/base chemistry that predicts mash pH and so can't be expected to predict it spot on. Even if the models were refined it is not practical to do the measurements on each malt that would have to be done in order to supply the malt's parameters to the models. Therefore you can expect a couple of tenths from modeling error. Try some of the other spreadsheets using the same inputs to get an idea of model variability.

If your readings are consistently coming in under 5 then I would suspect the meter but the stability check should make it clear that there is such a problem if there is one. Be sure you are using fresh virgin buffers.

I recall that AJ has reported that the mash pH can be slightly erratic for several minutes when using acid malt, but I don't think that a brewer should wait a half hour before checking pH. I typically collect and forcefully cool a sample at about 10 minutes in to the mash and follow that with another check at about 20 minutes. I don't typically find more than about a tenth variation in my system, but its a RIMS so the wort is constantly circulating. A mash sitting in a cooler with an occasional stir might not come to equilibrium as quickly.

Thanks for responses! I purchased the HM PH 200 meter. I think this is a good ph meter (nothing to back up that notion other than a few google searches) but I'm sure you both would know better. I'll try some other spreadsheets to see what I come up with. Thanks again.