Lager Starters - Best practices ??

menschmaschine said:

The two schools of thought among homebrewers are:

1. Ferment at room temp, cold crash (at least TWO nights before... it takes longer for lager yeast to drop out than ales when cold crashing), and decant off the unhopped beer before pitching. That way, most of the esters (etc.) produced from the warm ferment will be dumped down the drain with the starter beer and not into your lager.

2. Ferment the starter cold (~50s°F). Then the choice is yours... to cold-crash and dump the starter beer, or just pitch the whole thing (at high-krausen or fully fermented)... or maybe go half and half or whatever (so you're not dumping a whole gallon of unhopped starter beer into 5 gallons of your lager.)

Those are pretty much the two sides of it and some do something in between. For number one, the only suspicion I have is: once the yeast get used to fermenting warm, will there be a readjustment to ferment colder? And in this readjustment, will they produce flavor-active compounds (esters, diacetyl, phenols, etc.)? Or, because they are used to fermenting warm and producing flavor-active compounds at those warmer temps (lager yeasts will do that), will they continue to produce some of those compounds in your main ferment and result in off-flavors in the final beer?

If either of those 2 scenarios has merit, it's better to ferment cold. I'm not sure either way. At any rate, make a big starter (preferrably stepped up) plenty enough ahead of time (7-10 days isn't uncommon).

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Temperature: As much as there is debate about warm pitching vs. cold pitching there is debate about the propagation temperature for lager yeast. Microbiologists will tell you that yeast (lager and ale) should be propagated at 75 *F (25 *C) because that is the temperature at which they will grow best. Brewers however generally agree that yeast should be propagated at or slightly above primary fermentation temperature because the yeast should not get used to living and performing at higher temperatures than the primary fermentation temperature. Some home brewers report that yeast grown at temperatures above room temperature (80+ *F) tends to loose their flocculation characteristic which makes it harder for the yeast to drop out at the end of fermentation. Growing yeast at primary fermentation temperatures also avoids shocking the yeast when pitched because its temperature is already close to pitching temperature. The yeast propagation guidelines from the yeast bank Weihenstephan also suggest that the last stages of propagation are done close to fermentation temperatures.

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Q: Does a starter need to be kept at the same temperature as it is going to ferment the batch of beer later?

No, but there are practical limits to how high or low you can go.

Warmer starters (up to 98°F, 37°C) equal more rapid yeast growth, but using these very high propagation temperatures negatively affects the viability and stability of the resulting yeast. Very rapid growth or excessive growth can result in weaker cell membranes due to lower unsaturated fatty acid concentrations. Lager yeasts tend to be especially sensitive to high temperatures.

The cooler you ferment the starter (down to the planned fermentation temperature for the main batch) the slower the yeast growth, but the yeast can be healthier than yeast coming from a high temperature starter.

Keep starters between 65°F (18°C) and 75°F (24°C). A temperature around the low 70s (72°F, 22°C) strikes the best balance for the propagation of yeasts. Lager yeast starters can be kept a few degrees cooler and ale yeasts can be kept a few degrees warmer, but this temperature strikes a good balance of yeast health and efficient propagation for both types of yeast.

If you are going to pitch the starter at high krauesen, it is best to keep the starter within 5 degrees Fahrenheit (3°C) of the wort temperature of the main batch. Pitching a very warm, active starter into cold wort can stun the yeasts and with lager yeasts this can cause a higher incidence of petite mutants, which can negatively affect attenuation, flocculation, and increase hydrogen sulfide production.

You can add small amounts of cool wort to the starter over time, to bring the temperature down gradually, but it is really better to keep everything closer to fermentation temperatures from the beginning. Any time yeast sense a big drop in temperature, they slow down and drop out.

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