The temperature compost tea brewing works best at sits between 68-72°F (20-22°C) for healthy microbe growth. Too cold and bacteria barely move while too hot can kill the good ones you want to grow. Keeping your brew in this optimal temperature tea range gives you the best results for plants.
I noticed huge gaps in batch quality when brewing in my garage across different seasons of the year. Summer batches in 90°F (32°C) heat often smelled off and made thin tea that didn't foam right. Winter brews in 45°F (7°C) cold took twice as long and still came out weak with few bubbles.
My worst winter batch sat in the garage for three full days before I saw any foam form on top at all. By then the tea had that musty smell that tells you something went wrong during the brewing process. I dumped the whole batch and waited for warmer weather before trying again that year.
The brewing temperature controls how fast or slow microbes grow and multiply in your bucket. Below 55°F (13°C) they go nearly dormant and multiply so slowly that brewing takes days. Above 85°F (29°C) the good bacteria start dying while heat loving pathogens may thrive.
Cold weather brewing needs extra help to reach temps where microbes can grow at normal rates. An aquarium heater rated for 50-100 gallons works great in a 5 gallon bucket to warm things. Set it to 70°F (21°C) and let it warm water before you add compost to start brewing.
Hot summer days push temps past the safe zone and stress your good microbes during brewing hours. Move your bucket to a shady spot or brew indoors where AC keeps things cool for the batch. A basement floor often stays cooler than outside air and protects your brew from damage.
Temperature affects more than just microbe speed in your bucket during the 24-36 hour window. Warm water holds less oxygen than cold water does at the same air pump rate in your setup. Hot brews may need a stronger pump or more air stones to keep oxygen high enough.
Check your brew temp with a simple cooking thermometer dipped in water a few times during the process. Aim to stay within the 68-72°F (20-22°C) sweet spot as much as you can during brewing. Small dips or rises won't hurt but big swings can stress microbes and reduce quality.
Plan your batches around weather forecasts to hit the best brewing windows each week during season. Spring and fall often give you perfect temps without any heaters or cooling needed in your setup. Summer and winter require more work but good tea is still possible with the right gear.
Consistent temps throughout the whole cycle matter more than hitting the perfect number once at start. Wild swings stress microbes even if you average out to the right range over brewing hours. Set up your system to hold steady temps and batches will turn out better each time.
Read the full article: Compost Tea Brewing: The Ultimate Guide
