Lot of misinformation here, not necessarily wrong but not techniques that should be trusted to produce consistent results.
If you are looking to use a cultured
lacto vial, from WLP for instance, there are some things to consider:
1. You dont want to ferment with 100% cultured lacto at anything above 80F. The lacto culture from WLP is not designed for high ferment temps. I got this information direct from the supplier and can dig through my emails for a verbatim quote if so desired. I have fermented with it at 110F, 90F, 80F and 70F and have gotten by far the best results at the middle ground of 70F-80F max.
2. You want to limit, if not eliminate O2. This is still an anaerobic fermentation process, you dont want to just cover your mash with plastic wrap. This will allow entero bacteria to grow easier and the lacto will throw off weird flavors (sometimes cheese like, sometimes creamed corn like, sometimes approaching stale bar and potentially vomit and dirty baby diaper). In small amounts some O2 is good as it helps with growth and I find a subtle bit of a funky cheese/corn like aroma adds a bit of complexity.
3. Boiling is not really advisable pre lacto ferment. From everything I have researched there are some interesting chemical reactions that occur that make things more difficult for lacto and in addition can create some weird off flavors. I have only tried to boil pre lacto ferment once and I did not care for the results. This is in no way statistically significant and is more an anecdote. Take this with a grain of salt (especially if it is a gose
Finally, it is a much taken approach to sour mash to "just throw in some grains". To which I say is nonsense. This will not give you reproducible results, and is taking a big chance with your beer. If you want that risk and potential chance for more complexity in flavor (both good and bad!) then go for it.
So, with all that in mind here is my recommended method to properly mash souring your beer:
1. Mash as normal.
2. Lauter/Sparge into your boil kettle as normal
3. Bring the wort to 170F and hold for approximately 5 minutes. This will ensure that you kill all bacteria and yeast present on the grain and in the wort.
4. Cool wort to 70-80F and transfer to a fermentor. I use a dedicated sour PET fermentor.
5. Pitch pure lacto culture. No starter required. I have done starter and sans starter methods, neither sour the beer much quicker than just pitching a straight lacto vial in the wort. Again, personal preference on lacto starter.
6. Sour for 1-3 days depending on taste and if you have a pH meter, the pH. Personally, I find the sweet spot around 36-48 hours. I dont use a pH meter. If going by taste be sure you take into account the relative sourness as the wort is still very sweet. It is going to taste more sour post yeast fermentation.
7. Transfer the soured wort back to your boil kettle and proceed as normal.
That method has produced, time and time again, great sour beers. If I may brag a little, I brought a maibock I soured this way to NHC 2013 and actually received compliments from Dick Cantwell of Elysian on the beer.
Anyway, like anything in homebrewing and in life, take it for what it is worth. or dont.