As homebrewers, we're always striving to improve our craft. Most liquid and dry yeast packs are suitable for a single batch of standard alcohol beer. But if you are making a larger batch, higher alcohol, or the yeast is a little old or has not been treated well, this technique can help ensure an increase in yeast numbers. It can also create the optimal environment for yeast vitality and performance. Let's delve into the science and technique behind crafting the perfect yeast starter.
The Cell Count Conundrum: Why Starters Matter
Yeast starters can be crucial for achieving the ideal pitching rate, especially for high-gravity beers or when using suboptimal-viability yeast. The goal is to reach a cell concentration of approximately 100-200 billion cells per 2L starter, ensuring robust fermentation from the get-go.
Essential Equipment for Yeast Propagation
To create an ideal yeast starter, you'll need:
- Sanitising solution (e.g., Star San or iodophor)
- 2L or larger borosilicate Erlenmeyer flask
- Water bath container - can be as simple as your kitchen sink
- Precise thermometer (digital recommended for accuracy)
- 2L of water (preferably filtered or pre-boiled to remove chlorine)
- Magnetic stir plate
- Stir bar (4-6cm, PTFE-coated for easy sanitisation)
- 200g Dry Malt Extract (DME)
- Yeast nutrient (containing zinc, magnesium, and other essential minerals)
- Sanitised aluminium foil
The Technical Process: Crafting Your Starter
- Sanitisation: Use a no-rinse sanitiser with a contact time of at least 30 seconds to ensure all equipment is contaminant-free.
- Wort Preparation: Create a wort with a specific gravity of approximately 1.036-1.040. This equates to roughly 100g of DME per litre of water.
- Boiling: Maintain a gentle boil for 10 minutes to ensure sanitisation and to drive off DMS precursors.
- Nutrient Addition: Add yeast nutrients at a rate of 1g per litre of starter wort. This ensures optimal yeast health and reproduction.
- Cooling: Cool the starter wort in the water bath to a pitching temperature (18-25°C, depending on yeast strain) to prevent the formation of off-flavours and oxidation. However, be careful of rapid cooling, as this can cause the flask to break if there is a defect. Fold the sanitised aluminium foil over the opening.
- Yeast Pitching: For dried yeast, rehydrate according to the manufacturer's instructions before pitching. Allow the package to reach room temperature for liquid yeast to prevent thermal shock.
- Oxygenation and Agitation: Use the stir plate to maintain dissolved oxygen levels between 8-10 ppm. This is crucial for yeast reproduction and lipid synthesis.
- Propagation: Allow the starter to propagate for 12-18 hours. During this time, yeast will go through lag, growth, and stationary phases.
- Flocculation: After fermentation, allow the yeast to settle for 6-12 hours. This separates the yeast from the spent starter wort.
- Decanting: Carefully remove the supernatant, leaving behind the concentrated yeast slurry. This reduces the introduction of oxidised beer into your main batch.
- Pitching: Introduce the yeast slurry to your main wort, aiming for a pitching rate of 0.75-1 million cells per millilitre per degree Plato for ales or 1.5-2 million cells per millilitre per degree Plato for lagers.
Advanced Considerations
- Oxygen Saturation: Consider using pure oxygen in the wort for optimal dissolved oxygen levels, especially for high-gravity starters.
- pH Monitoring: Maintain a pH between 4.5-5.5 for optimal yeast growth and health.
- Serial Stepping: Consider multi-step sugar additions for very high gravity beers to gradually acclimate yeast to high alcohol environments.
- Cell Counting: Use a hemocytometer or methylene blue staining technique to measure cell count and viability accurately.
This is but one method for making a yeast starter, but there are also other methods such as the shaken not stirred method and using dextrose or LME for making the starter.
By focusing on these technical aspects, you're not just making a starter but creating an optimised micro-environment for yeast proliferation and vitality. This attention to detail will translate into cleaner fermentations, more complete attenuation, and superior beer quality.
Remember, consistency in your starter process is key to reproducible results. Keep detailed records of your starter parameters and correlate them with fermentation performance to continually refine your technique.
Happy brewing, and may your fermentations be vigorous and your beers be exceptional!
MYO Drinks
Helping you to make your own Great Batch from Scratch.