We want to start by saying that white blotches do not always mean you have a problem.There are two main types of blotches that brewers have to worry about. As for the explanations, we have good news for some and bad news for others. If you just have some white things floating around on top of your fermenting beer, 95% of the time you have nothing to worry about. Usually this is just some krausen/ foam, yeast coming together, or proteins. All of which are perfectly fine and normal. They will go into solution as you move on in the process.
However, if you have white blotches and they are starting to form what look like spider webs, you have a major issue.Molds are non-chlorophyll plants that range in size from single spore to large aggregates. Commonly occurring types of species are Mucor, Penicillium, Aspergillus, Cladosporium, Geotrichum, and Rhizopus. Most molds are able to grow well at room temperatures, with the optimal range being 75 - 85 °F. Although some species can grow at even warmer temperatures. However, this high a temperature would not be good to make your beer at anyway. Molds are normally aerobic organisms that can grow over a wide range of pH ranges, but they do tend to like the more acidic pH range.
Now that you know what you’ve got, how do you get rid of it?If it is very early on in the formation, you could skim the mold off with a sterilized spoon. This should help remove most of it. Then you need to get the fermenter into an area below 60 °F to stop the growth. The colder you can get the beer, the better. Just don’t freeze it. This will stop the growth and the beer will be fine. It will have a slight medicine flavor, but for the most part should be fine.
If the entire top of the fermenter is covered with mold you are best to toss out the beer.The mold will only continue to grow and make the beer nasty. There are times in brewing when it just isn’t worth trying to save the beer. Make sure to clean all of your equipment with a bleach and water solution before you use it again. Mold and bacteria can be hard to remove so you need something very strong to kill them. Bleach usually works well for this. Make sure to soak everything in clean water after the bleach solution.