Pitching Enough Yeast
“I used the packet of yeast that came with the kit.”
“How old was that?”
“A couple of years I think. It seemed to work okay.”
The above exchange was part of a real conversation I had about brewing a beer, me being the questioner. And the other person was not a beginning brewer, nor an ignoramus, but a very intelligent and well-educated scientist. And worse, his idea of “working okay,” and that of many other homebrewers I have spoken to, was that fermentation was noticeably underway after one to two days. Craft brewers, as well as writers in this magazine, have frequently laid down strictures about the need to pitch sufficient amounts of active yeast, but it seems that many homebrewers seem to still ignore all ofthese recommendations.
Is pitching rate really that important? Does it matter if the yeast takes a bit more time to get going, so long as the beer isn’t infected and tastes all right? Well, actually, yes it does matter, because for a start if you consistently have long lag times you will brew infected beer sooner or later. Also, even if it is free of spoilage organisms your beer will not taste “all right,” it will taste like “homebrew.” Ask any professional brewer and he will tell you that the most common mistake made by amateurs is under pitching their yeast, and this is what causes that homebrew tang. Garrett Oliver, from New York City’s Brooklyn Brewery explains that an insufficient amount of healthy cells means that the yeast will struggle and throw off a lot of estery profiles, “which is a common flaw in homebrews.” He also points out that you will find in a commercial brewery that warm fermentations, “are very clearly active within 12 hours.”
What prompted this column was a letter from a BYO reader about Jamil Zainasheff’s recipe for Maibock, which quoted a 15-L starter for a 5 gallon (19-L) brew. The reader seemed to think that that meant he had to add all of the 15-L of his liquid, and that just is not how starters work. Quite simply, you need to pitch only the yeast from the starter, not the liquid. What this means is that once the high head or kräusen has formed and started to subside, you decant up to 90% of the liquid (depending upon how well the yeast flocculates), swirl the vessel to loosen the sediment and add that to the wort in the fermenter. In case you are wondering whether Jamil and I have different viewpoints on this, I confirmed with him that that is exactly what he meant. And of course, in the case above you would probably finish up with 1.5 to 3-L (0.4 to 0.8-gallon) of liquid to pitch, a much more reasonable volume to handle. As the response to the reader’s inquiry pointed out, you could in any case reduce the size of the starter by using two packets of liquid yeast rather than one. Jamil himself also recommended in his recipe that you could use 5 packets of liquid yeast instead of making a starter.
Jamil also pointed out that an even better method would be to make a smaller beer first, and to crop the yeast from that for pitching into the bigger beer. That of course is exactly how a commercial brewery would approach it. For example, where I brew — BrüRm@BAR in New Haven, Connecticut — we take the settled yeast from our Toasted Blonde and use it to pitch all our other beers, Toasted Blonde is our blandest and weakest beer at 1.040 (10 °P). This is also where I usually get my yeast when I am brewing at home. Obviously, you could do the same if you live close enough to an obliging craft brewery. If you don’t have such a source you could brew a “small” beer at a similar gravity, and use the yeast sediment obtained at racking from the primary to pitch into your bigger beer. If you do that you should not re-pitch yeast from a beer with OG much above 1.050 (12.5 °P), nor keep the yeast for longer than one to two weeks before re-pitching. Either of these mistakes will result in a batch of yeast, which is already “tired,” and you will negate the reason for doing this procedure in the first place. Yet what do you do if you can’t do that, because you don’t have the time or the space or whatever reason? Then you are back to making a starter to give you an appropriate amount of yeast for a big beer.
But how do you know what is an “appropriate amount?” Well, you could go to Jamil’s website, www.mrmalty.com, and go to the “Yeast Tools” section where there is a pitching rate calculator. You just punch in the beer type, original gravity, volume, type of yeast (liquid, dry or slurry), and type of starter and it will tell you what volume of starter you need. Wyeast (Wyeastlab.com) also has a pitching rate calculator on their website, although it is simpler than the one on mrmalty.com. Or you can make some straightforward calculations yourself. If you consult various brewing textbooks you’ll see that you need 1 million cells per milliliter/°P for a “regular” beer at around 10–12 °P. Or, if you prefer, this is close to 1 million cells/mL/4 degrees SG (the latter being OG x 1000), for a beer at 1.040 to 1.050.
So, taking the lower figure, for 5 gallons (19 L) at 1.050 (12.5 °P) you need:
5 x 3.78 x 1000 x 106 x 50/4 = 1181 x 109 = 238 B cells
As the original gravity increases the amount of yeast increases, so that for a beer of OG 1.080 (19.3 °P) or more you would need up to twice this amount, or about 400–500 billion cells. That is because you need sufficient yeast for the fermentation to proceed at a normal rate — by which I mean that the desired terminal gravity is reached in 3–5 days. If it doesn’t go at a normal speed, then the yeast is going to be struggling to finish its job of attenuation when it is in a high alcohol environment, which will make it struggle even more. Note also that lager brewers generally like to pitch up to twice as much yeast as ale brewers do, to counteract the fact that their cooler fermentations result in a slower absolute fermentation rate.
Let’s say we want to make 5 gallons (19 L) of a strong ale with an OG of 1.090 (21.5 °P) (the recipe appears at right). I don’t want this to be too sweet, so we want good attenuation with a finishing gravity no more than 1.025 (6.3 °P), which means aiming for a pitching rate of around 500 billion cells. We shall consider only liquid yeast strains for the moment, and White Labs states that their vials contain 75–150 billion cells; clearly that is not enough for this beer, so that we would need around five vials for direct pitching. But White Labs recommends a starter, and say that 1 vial in a 0.5-gallon (2-L) starter will give about 240 billion cells in two days.
Wyeast numbers are very similar as they state that their Direct Pitch Activator packs contain 100 billion cells, and a 0.5-gallon (2-L) starter would yield 240 billion cells. So in either case we are looking at 2 packs or vials and a 1- gallon (4-L) starter to get up to around 5 billion cells. Actually these figures for growth might be somewhat low, for a normal fermentation results in a three-to-five-fold increase in the amount of yeast. However, they know their yeasts better than I do, so we’ll go with those figures.
Therefore we need to prepare a starter, and for that we want a wort at about 1.040 (10 °P). If you should happen to have that on hand, fine, but you will probably have to prepare it separately. Malt extract will serve well for that, and since I am planning on using an amber extract in the recipe we’ll use that for the starter as well. So for one gallon (3.7 L), we’ll need 1 lb. 2 oz (0.5 kg) of amber malt extract. Dissolve the extract in the water, and bring to a boil. Add 0.5 oz (14 g) of East Kent Goldings hops — this will give around 40 IBU, which is what we’ll target in the beer, and we need the hops here so the yeast can to adjust to this environment, and to provide some preservative characteristics to the wort. Boil for 30 minutes, transfer to a sterilized jar, cover with cling film, or, if the jar has a narrow neck, stuff it with cotton wool. Cool as rapidly as possible to around 70 °F (21 °C), agitate well, or better still oxygenate for one to two minutes, then pitch the two yeast vials or packs. In the latter case, activate the packs by “smacking” as instructed by the suppliers, before adding to the starter. Keep in a warm place for two days, by which time there should be a good amount of sediment of yeast in the jar. Pour off at least half the liquid, swirl the remainder until the sediment is fully suspended, and pitch this to the wort, using the extra amount to adjust your final volume to 5 gallons (19 L). Don’t forget to agitate, or better oxygenate the wort after pitching.
There are a couple of points about this, the first being that you have to plan ahead for your brew day so that your wort is ready when your starter is ready! Secondly, I have assumed that we have made a “simple” starter; that it isn’t agitated nor continuously aerated during its fermentation. Both of these latter approaches will accelerate growth, but I don’t have space to deal with them here, and in any case they would require a more complicated setup. And of course, I have assumed that we have chosen yeast strains which flocculate quite well (but not so well that they’ll settle out before completing attenuation). I have recommended two yeast strains, which you will see in the recipe below.
Conclusion
The recipe I have given is quite a simple one; it will still give a satisfying strong ale, but the real point about it is the yeast and how it is pitched. This simple fungus is amazing and capable of doing some wonderful things for us, but like us it does have its limitations. It is a brewer’s friend, so treat it like a friend and make its task as easy as possible. You would not expect a right-handed baseball starter to pitch well with his left arm, and you similarly shouldn’t expect an insufficient amount of yeast to be capable of producing top quality beer.
Cy Young Strong Ale
(5 gallons/19 L, extract only)
OG = 1.090 (21.5 °P) FG = 1.020-1.025 (5-6.3 °P)
IBU = 40 SRM = 30 ABV = 9.3-10.0
Ingredients
13 lb. 10 oz. (6.2 kg) amber* malt extract syrup
12 AAU East Kent Goldings hops (60 mins.)
(2.4 oz./68 g at 5% alpha acids)
10.8 AAU East Kent Goldings hops (0 mins.) (2.7 oz./76 g, at 4% alpha acids)
Wyeast 1098 British Ale yeast or White Labs WLP002 English Ale yeast (starter prepared as in text)
(*Use a syrup brewed with crystal malt or one that uses both crystal/caramel and Munich malts.)
Step by Step
Dissolve the extract in 3 gallons (11 L) of warm water, top up to 5 gallons (19 L) and bring to a boil. Add the hops per the above schedule. Cool to 70–75 °F (21–24 °C), and pitch the starter. Aerate thoroughly or oxygenate. Fermentation should be visible within 12 hours. Leave for 7 days then rack to the secondary. Condition for up to one month before packaging.
