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I've read a few accounts of brewers using slow temperature increments to bring out particular flavours from the yeast that they're using. For example, stepping up 1C or so every day over a few days.

Specifically I've read suggestions that a saison yeast (e.g. wyeast 3711, 3724) being stepped through the recommended range over a week - 18 to 25C (or higher).

Can the same flavour profile be obtained by letting the brew naturally fluctuate between the two extremes or is it crucial to increment the fermentation temperature? I'm using 3711 in a saison but I'm more interested in the general answer.

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Temperature swings will cause the yeast to drop out and not dry out your beer.

At the end of fermentation, most of the nutrients and food have been consumed and the yeast will want to drop out and go dormant. With repeated temperature swings, most if not all of the yeast will go dormant with each drop in temperature, and it takes a lot more warming or additional sugars to get them started again in the nutrient-deficient environment, which means in practice they stay dormant.

By raising the temperature, the increased metabolism allows the yeast to consume compounds that normally ferment much slower, such as maltriose at a rate that can sustain the cell so that it doesn't go dormant.

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  • Ahh cool, this explains why the step up is important, as opposed to say a step down or other temperature curve.
    – Mark McDonald
    Oct 4, 2012 at 8:50
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In Jamil's podcast on brewing saison, he notes that the reason for stepping up is to achieve a high level of attenuation (dry beer), while minimizing fusel alcohols.

The natural fluctuation that you mention is the result of heat being generated BY the yeast as it metabolizes the sugars/carbs in your wort. This can raise the temperature of your fermenter considerably during the active phase of fermentation (on my system (ale pails/carboys), I've seen it as much as 5-10 degrees). This is why it is important to monitor your fermenter temp, and ambient air temp can be far less relevant.

"Whats a couple of degrees difference?", most people ask. Remember that yeast are SINGLE celled organisms. We are 50 trillion-celled organisms. 65 degrees F and 66 degrees F feel the same to us, but for yeast its could be the difference between Chicago in December and Tuscon in August. I certainly eat, digest (and likely reproduce) very differently in those two climates!

The shorter answer is by keeping control of the temperatures at which yeast are metabolizing your sugars, you are keeping control of the compounds they make, which will ultimately flavor your beer/wine/other fermented beverage.

I have made saisons without temp control, and they are good. However, I can defintely perceive fusels (hot alcohol). If you really want the yeast's spicy, fruity phenols to be apparent, with a dry finish, the step up is critical.

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  • one other thing to note here, when you do raise the temperature, sometimes the steady or increased airlock activity can just be CO2 escaping out of the solution as it warms. Actually it usually is.
    – Pietro
    Oct 3, 2012 at 14:12

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