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Wort can be soured in the primary fermenter before adding other yeasts. This is generally a good approach for brewers who aren't concerned with pasteurization and infections of their cold side equipment. This has the advantage of possibly producing a more complex sour beer overall, or at least a sour beer that will evolve over time. It has the advantage over a more traditional [[Mixed Fermentation]] in that Lactobacillus is used to guarantee at least a certain level of sourness. This is also a good process to use for making a [[Berliner Weissbier]].
The process is very similar to the sour worting technique, except the wort is never pasteurized after it is soured. The all grain brewing process is the same for any all grain brewing process, except that after the boil the beer is only chilled to the recommended temperature for the Lactobacillus strain that the brewer is going to use. Using grain husks for souring with this method is not advised since the grain will stay in the fermenter during primary fermentation, and unwanted microbes on the grain husks would potentially have a longer exposure to the wort. Thus, there is little concern of developing [[Butyric Acid]] or [[Isovaleric Acid]] with this method. There is also the option of [[Mixed_Fermentation#Reusing_a_Sour_Yeast_Cake|using a sour yeast cake]] from another sour beer as the bacteria inoculation.
Once cooled to the desired temperature (usually around 90-120°F or 32.2-48.8°C), the wort is racked to the primary fermenting vessel. Note that the wort should contain a low amount of IBU's when using this process since IBU's can inhibit many (but not all) species of [[Lactobacillus]]. Less than 6 IBU's is a good guideline in general. It may or may not be advised to create a Lactobacillus starter (see the [[Lactobacillus]] page) before hand. Once the wort is racked to the primary fermenting vessel, the Lactobacillus culture is added directly to the fermenter. No other yeasts are added at this time. The Lactobacillus bacteria is allowed to incubate by itself in the wort for 2-5 days with the before mentioned target temperature maintained throughout the incubation period (some Lactobacillus species/strains may continue to produce acidity under lower temperatures). The exact time frame of incubation depends on the species/strain of Lactobacillus, the manufacturer's recommendation, and the brewer's desired acidity level. Acidity can safely be measured with a reliable pH Meter throughout this time. If possible, it is advised that the brewer fill the head space of the fermenter with CO2. Some brewers have reported that this helps to reduce sulfur production, but if Brettanomyces is added to the beer later on in the process and allowed to age, this shouldn't be a concern.