# Where the jar sits decides the brew > Cultures for Health puts a number on every temperature band, from the ideal window to the point where mold risk climbs to the heat that kills a culture outright. Topic: Temperature Read it if the house runs cold, or before moving a jar somewhere that seems warmer. ## The source under review - Article: Kombucha Temperature: Brewing and Fermenting - Published by: Cultures for Health - Kind of source: Supplier - Dated: June 2023 - URL: https://culturesforhealth.com/blogs/learn/kombucha-temperature-brewing-fermenting - Last checked by Kombrewcha: 2026-09-17 --- Two brewers can follow the same recipe to the letter and open two different drinks. Same tea, same sugar, same culture, same ten days. One is balanced and one is still syrupy. The variable almost nobody writes down is where the jar was standing. 🍵 This article is the one that puts numbers on it. ## What it gets right It gives a band for every condition rather than a single ideal, and each band comes with what actually happens inside the jar: - **75–80°F is the target**, and the article makes the useful point that it matters most in the first three to seven days, while the brew is still acidifying. - **60–85°F works**, with the brew simply running slower or faster inside that span. - **Below 64°F the bacteria turn sluggish** and cannot acidify quickly enough to hold mold off. The risk here is not a slow brew. It is a lost one. - **Above 100°F bacterial activity stops** and the result turns sharply vinegary. - **At 109°F and above the yeast start dying**, and a culture will not survive more than a couple of days. That last pair is what makes the article worth reading rather than skimming. Warmth is usually treated as the safe direction to err in, and it is not. There is a ceiling, and past it the culture does not recover. The practical advice is sound too: a heating mat or a warmer shelf for a cold kitchen, a cooler spot or a fan for a hot one, and an explicit warning against heat lamps and light bulbs, which heat unevenly and cook one side of the jar. ## What to bring back to a brew **Measure where the jar is, not where the thermostat is.** A thermostat reads the middle of a room at chest height. A jar on a tiled counter under a window is living somewhere else entirely, often several degrees colder, and that gap is the whole difference between ten days and twenty! **Treat 64°F as a line rather than a preference.** Below it the question stops being how long the brew will take and starts being whether it will make it. A first-time brewer who is worried about mold is worrying about the right thing, and this is the single number that does most to prevent it! 😌 **Do not chase warmth with anything that has a bulb in it!** A mat under the vessel warms evenly. A lamp beside it makes one wall of the jar far hotter than the reading suggests, and that is how a culture gets cooked while the thermometer says everything is fine. Our own suggested durations assume a room in the 75–80°F band, which is where this article and [Kombucha Kamp](/reading/why-your-brew-is-taking-so-long) both land. A cold kitchen does not mean the numbers are wrong. It means the range runs long, and it is the low end of the taste window that moves first. ## Worth knowing about the source Cultures for Health sells cultures and fermentation supplies, and the article is unattributed beyond the house account, so there is no individual brewer's judgment to weigh. The figures line up with what the university sources say, which is the reason to trust them here rather than the byline. It is a reference page, not a troubleshooting guide. It will tell us what 68°F does to a brew. It will not tell us what the jar should look like on day six. For that, read a practitioner. --- This is a review by Kombrewcha of a third-party article. Kombrewcha is not affiliated with Cultures for Health. Read the original at https://culturesforhealth.com/blogs/learn/kombucha-temperature-brewing-fermenting.