A yeast starter is one of the simplest techniques you can use to save money and ensure youre pitching healthy, viable yeast. It multiplies your yeast before brew day so you get a faster start, cleaner fermentation, and less risk of off-flavours. This guide walks you through exactly how to make one.
What is a yeast starter (and when should you make one)?
A yeast starter is a small batch of low-gravity wort that you ferment ahead of brew day to build cell count and vitality. A starter essentially provides yeast with all the building blocks they need to reproduce in a process called budding.
WE WOULD RECOMMEND MAKING A STARTER WHEN:
- Using liquid yeast, especially if it’s more than 2 months old. Especially for lagers.
- Brewing lagers or higher-gravity ales (OG ≳ 1.060).
- You want a quick, clean fermentation with fewer surprises.
What you’ll need:
EQUIPMENT:
- 1–5L Erlenmeyer flask (borosilicate ideally).
- Stir plate + stir bar (best growth but optional), or plan to shake intermittently
- Aluminium foil
- Sanitiser (no-rinse)
- Small saucepan (if not boiling in the flask)
- Thermometer
- Funnel (optional, but handy)
- Fridge for cold-crashing
INGREDIENTS:
- Light Dry Malt Extract (LDME)
- Yeast nutrient (optional but recommended)
- Yeast
- Clean water
How big should the starter be?
The best way to calculate your starter size is by using a yeast starter calculator. We usually use the starter calculator built into the Brewfather Brewing Application.
A simple rule of thumb for classic starter wort is 100 g Light Dried Malt Extract Powder per 1L of starter volume.
Don’t stress about nailing perfect numbers. Sanitation is the main thing to be concerned about as bacteria that is introduced into your starter wort will propogate faster than the yeast and can lead to you accidentally cultivating bacteria instead of yeast.
Step-by-step process (1L starter example):
- Two or three days before brew day sanitise the flask, foil, funnel, scissors, and the outside of your yeast pack. Everything that will come in contact with your starter wort must be thoroughly sanitised. It is better be over cautious here.
- Weigh out 100g of Light Dried Malt Extract and add to your flask that you plan on boiling your starter wort in.
- Add clean water to reach 1.0L of final volume in the flask or saucepan.
- If you are using a magnetic stir plate add the teflon coated stir bar at this point.
- Add a small pinch of yeast nutrient, ensure to follow the manufacturers dosage rate outlined on the packet or materials sheet for the product.
- Add a small amount of anti-foam or distilling conditioner to the starter wort to stop a boil over.
- Boil the entire starter liquid for 5 minutes to thoroughly pasteurise the wort. If boiling the entire Erlenmeyer flask we would suggest leaving the foil cap on the flask while it boils to sanitise this too.
- Cool the wort to 20-22°C by sitting the flask in cool water. Borosilicate can handle large temperature changes however we would suggest letting the flask cool slightly before submerging it in cool water to minimise material fatigue which can cause the glass to eventually break. Make sure the foil cap sits over the top of the flask during this process.
- Pitch your yeast into the starter liquid. If using liquid yeast make sure the pack comes to room temperature before adding to the starter liquid. Ensure the liquid yeast packed is shaken well to resuspend all the yeast in the pack.
- Put the foil cap loosely back on the top of the flask, this doesn't need to be airtight as we want oxygen to diffuse into our starter liquid and Carbon dioxide to leave.
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If you're using a magnetic stir plate set a steady vortex and leave it to stir. If you're not using a stir plate vigorously shake the starter to resuspend yeast and knock dissolved gas out of the starter mixture whenever you walk by. Usually you will see visible signs of activity after 12-24 hours.
- Keep the starter warm while the cells grow. Don't worry about fermenting lager yeast too warm as we will be decanting the wort off the top of the yeast later. The warm temperatures help our starter grow faster.
- After 24-48 hours your starter has usually finished, you will no longer see signs of fermentation and the yeast will start to flocculate if the stir plate is turned off.
- Refrigerate the starter flask for 24-48 hours. This drops the yeast to the bottom of the flask into a daily compact cake.
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On brew day, pour off most of the clear spent beer, leaving the yeast cake behind.
Add a small splash of your fresh, sanitised wort or cooled boiled water, swirl to re-suspend the yeast, and pitch into your fermenter.
If you're in a time crunch:
If you're on brew day a short starter can be made and pitched at high-krausen (when yeast is super active in the starter vessel). Instead of gaining a huge amount of yeast cells you'll have very viable yeast. It's not ideal but still works well, there's even debate as to whether this method is more effective.
Tips for best results:
- Sanitation first: starters are low-hop, low-gravity, and perfect for microbes, so keep everything as clean as possible.
- Don’t over-gravity: aim for ~1.037 - 1.040; higher gravity can slow growth and stress yeast.
- Add nutrient: especially useful with older yeast packs or step-up starters.
- Stir plate vs shaking: constant stirring increases growth compared to no stirring.
- Do a visual check: signs of a pellicle or a ropey character can indicate contamination, so can intense off flavours such as solventy.
Troubleshooting:
BOIL OVERS:
Lower the heat, use a bigger vessel, and consider a drop of anti-foam.
NO KRAUSEN?
On a stir plate, krausen can be small or absent but growth is still happening. Let it run 24–36 h.
STARTER SMELLS BAD:
If it’s just “starter twang,” you can decant and pitch the slurry. If it smells infected or looks ropey/filmy, dump and start fresh. Its better to be safe than sorry, however many people confuse yeast smells with infection.
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