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Once the level of acidity is reached (this can be tested with a reliable [[PH_Meter|pH meter]], or in the case of using a pure culture can safely be taste tested), the wort is brought to a boil. The wort may be boiled normally in the case of any style of beer that requires a longer boiling process, or it may be boiled for no more than a minute or two in the case of making a [[Berliner Weissbier]]. Technically speaking, the wort doesn't need to be boiled at all (this is called [http://www.garshol.priv.no/blog/331.html Raw Ale]). Heat pasteurization at 170°F (76.6°C) for 15 minutes should kill the ''Lactobacillus'' culture being used to sour the wort <ref name="pasteurization" />.
Deciding whether or not to boil the wort can also depend on whether or not there was a considerable amount of alcohol produced, which commonly happens when the wort is contaminated with yeast. Pure cultures of ''Lactobacillus'' do not show typical signs of fermentation that we are used to seeing with yeast fermentations, such as forming a krausen, producing a lot of CO2, or fermenting wort more than ~1.005 gravity points (see [[100% Lactobacillus Fermentation]]). If a yeast contamination produces a significant amount of alcohol during the souring process, then this presents a problem when it comes to boiling. Although 100% pure ethanol boils at 173.1°F/78.4°C <ref name="boiling_of_alcohol">[http://chemistry.about.com/od/moleculecompoundfacts/f/What-Is-The-Boiling-Point-Of-Alcohol.htm Boiling temperature of ethanol]</ref>, the lower the concentration of ethanol in the wort (technically beer at this point if it has been fully attenuated by yeast), the higher the temperature required for boiling off the ethanol. For example, at 5% ABV it takes approximately 197°F/92°C for the ethanol to boil <ref>[http://www.clawhammersupply.com/blogs/moonshine-still-blog/12243869-making-moonshine-still-temperature Making Moonshine: Still Temperature. Retrieved 01/11/2016.]</ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1212116758816536/?comment_id=1212140998814112&comment_tracking=%7B%22tn%22%3A%22R%22%7D Conversation with Russell Carpenter on MTF. 01/11/2016.]</ref>. Time is also required to boil off the ethanol, so this may not be as big of a concern as it first appears (''warning: vaporized ethanol is highly flammable)''. Another and perhaps more important consideration is that boiling and high heat pasteurization temperatures can have a negative effect on the flavor of fermented beer. Beer already has anti-bacterial properties, such as low pH, presence of alcohol, and hops (although hops may not be present in wort being soured), so higher pasteurization temperatures aren't necessarily required for beer. For these reasons, the beer industry commonly heat pasteurizes beer at '''140°F/60°C for 15 minutes''', and this is also adequate for pasteurizing soured wort that accidentally fermented do to yeast contamination <ref>[http://www.sciencedirect.com/science/article/pii/S0023643806002854#bib16 A suitable model of microbial survival curves for beer pasteurization. Sencer Buzrul. 2006.]</ref>. Although the yeast will be killed during the pasteurization, so will the ''Lactobacillus'', and the brewer can trust that equipment downstream shouldn't get contaminated. Other options are to simply dump the batch and start again with a pure culture of ''Lactobacillus'', or do not pasteurize and let the ''Lactobacillus'' live. If the ''Lactobacillus'' is not pasteurized and allowed to live, the soured wort/beer should be treated with care so that it does not contaminate the rest of the brewery (see [[FAQ#Do_I_need_separate_equipment|'Do I need Separate Equipment?' FAQ]]).
Boiling soured wort that hasn't had an accidental yeast contamination (and thus still has a high specific gravity) probably has less of an effect on the flavor than it does on fully fermented beer. Other than lactic acid, the flavor components that different strains of ''Lactobacillus'' produce are not well defined, so it will be difficult to determine if boiling soured wort will have a negative impact. However, brewers who boil kettle soured wort don't often report that the boiling causes flavor issues <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1464590560235820/?comment_id=1465040723524137&reply_comment_id=1465146946846848&comment_tracking=%7B%22tn%22%3A%22R4%22%7D Conversation with Bryan from Sui Generis blog on MTF regarding boiling soured wort. 11/10/2016.]</ref>.