How do I increase the sulphur production in a lager?

Question

In my past experience, my lagers have no perceptible sulphur. I understand that the "rotten egg" sulphur (H2S) is undesirable, but every great lager I have tasted has at least a hint of matchstick sulphur (SO2), sometimes fairly pronounced. I found a lot of articles on how to remove it or mitigate it, but little to nothing on how to produce it.

I have tried different fermentation temperatures (low 40Fs to mid 50Fs), but they all taste the same to me; rather bland and "un-lager-ish". I have tried different yeasts (wy2124, wy2007, wlp830, but mostly use w34/70 (which I believe is perhaps the same as wlp 830/wy2124). I have also tried wy2278, but it's been a while. I actually purchased this for my next lager because it specifically mentions sulphur production.

I normally make a starter, using DME and size by the numbers from Mr. Malty (or pitch 2 packs of w34/70). I also usually chill the starter and decant before I pitch it, so I don't get too much DMS from the starter. I've even tried fermenting the starter at lager temps, though it didn't seem to have any perceptible difference.

My "usual" technique is the one described in Palmer's introduction to Jamil's "Brewing Classic Styles", page 43, where the wort is chilled to 7C before pitching, then raised to 10C over the next 3 days. I certainly don't do everything right every time, but like I said, my lagers just don't have that classic taste I get from nearly every craft lager.

If you have any recommendations or corrections to my technique, it would be greatly appreciated. Lagers are a style I have yet to even pull off, much less master :)

Answer 1

I did some research and found there actually are a number of factors influencing the production of sulfur dioxide (SO₂) specifically (as opposed to H₂S or DMS) that can be controlled:

• SO₂ production is favored by higher original gravity. Basically this is because sulfite synthesis by yeast requires energy and more energy available as fermentable sugar means more chance for sulfite accumulation. Higher glucose levels in particular have also been correlated to increased SO₂, though the reasons for this are not entirely clear.

• Decreased wort oxygenation (and/or wort lipid) levels will increase SO₂ levels. The reasons are a bit complex: these factors favor increased levels of yeast growth; more yeast growth means more amino acid uptake from wort; amino acids in general inhibit sulfite synthesis from sulphate; hence, positive effects on extent of yeast growth = positive effect on yeast amino acid levels = negative influence on SO₂ levels. Similarly, yeast in poorer health will experience less growth and resultant elevated levels of SO₂. A specific correlation exists between the length of pre-pitch starvation of stored yeast and sulfite levels.

• A lower ratio of amino acids (FAN) to fermentable sugars in wort favors SO₂ accumulation, due to the amino acids' previously mentioned inhibitory effect.

_{Info above from the unimpeachably definitive Brewing Yeast and Fermentation.}

• This paper suggests yeast pitching rate and wort pH are also factors: "Sulphur dioxide formation is also increased by using high wort pH, low wort oxygenation or a low yeast pitching rate".

• Here, abstract #9 (on page 124) states "SO₂ formation increases with higher pH and is temperature dependent with maximum at 14-17 C".

Some additional thoughts of my own, without citations:

• Since an important precursor to sulfite is sulphate, having water with higher levels of SO₄^-- may encourage more resulting SO₂, provided the fermentation conditions are right.

• If you can and aren't already, try to explore fermentation under pressure. It could help keep volatile sulfur compounds in the beer that would otherwise be stripped out by CO₂ formed and dissipated during fermentation. Most sulfite accumulation happens towards the end of fermentation (as sulfites cease to be used by yeast for amino acid synthesis) so you should be able to effectively trap this in a pressurized fermentation.

• Sulfur compounds being gaseous and volatile, lower temperatures could help prevent them from dissipating from beer while conditioning, especially if kept under pressure.

• Seems like you've explored a number of strains without luck, but you might find they react differently to altered fermentation strategies. If you find a particular one that's nice and sulfur-y, I'd stick with it. Unfortunately I can't recall those strains from my own experience that give elevated SO₂.

So to boil it down: increase your gravity; cut back on oxygenation; decrease FAN levels (maybe by trying lower-protein malts or eliminating proteolytic enzyme activity in the mash); shoot for higher wort pH; decrease pitching rates; increase water sulphates; keep fermentation warm and conditioning cool (and, if possible, under pressure) to discourage dissipation; and, if you really want, you could try stressing out your yeast by storing it for longer periods.