Five Hundred Ninety-Three Billion

592,700,000,000 - Whew, that’s a big number. It’s also the number of viable yeast cells that I needed to pitch into my Helles Bock this weekend in order to give my beer the best chance of success. The best chance for the yeast to not stress out and start creating unwanted flavors.

So, how did I get there knowing that the average liquid yeast packet only contains 100B cells? (And that’s at the point they package it, viability decreases with time, leaving you with even fewer cells). Did I go to Hoppin’ Grape and purchase 7 packs of liquid yeast? No, I actually did something much more cost effective. I made a starter.

Starters seem like a complicated step to a lot of homebrewers, and some brewers will go so far as to say that they’re an unnecessary step. I won’t argue that they’re always necessary, but I do personally make starters more often than not. I like the strong start to fermentation I get when I use a starter, and I like knowing that my army of yeasty boys has every advantage as they work to make beer from the wort I gave them.

Acetaldehyde and Diacetyl

Under pitching yeast can lead to several undesirable flavors and issues with your beer. All yeast produce acetaldehyde (unripe apple) and diacetyl (fake butter) as they ferment, however, if there are enough active yeast at the end of fermentation then the yeast will ‘clean up’ after themselves and reabsorb these chemicals, breaking them down below the flavor threshold.

Esters and Phenols

If there isn’t enough yeast in your wort, then what yeast is present must undergo an overly stressful growth phase. When yeast are stressed during this phase they create unwanted amounts of esters and phenols. Esters are compounds responsible for fruity aromas and flavors. While some esters are desirable in certain beers (isoamyl acetate is the ester responsible for the flavor of bananas, and is also created by hefeweizen yeast, giving weissbiers their characteristic banana flavor) most ales only want low amounts of esters, and a clean lager should have no perceptible fruitiness. Phenols are the compounds responsible for the olfactory bouquet in peated scotch. While hints of burning tire and iodine are wonderful in the right scotch, very few beer drinkers want them in our beer. Pitching enough healthy yeast into your wort can help prevent the stresses to the yeast that cause these compounds.

Dimethyl Sulfide

This off-flavor isn’t created by the yeast but rather can be eliminated by using enough healthy yeast. All fresh wort also contains some amount of Dimethyl Sulfide (DMS), this chemical produces a cooked or creamed corn aroma and flavor. DMS is created in the boil, and is a rather volatile chemical. As such, if you pitch enough healthy yeast, then the off-gassing of CO2 during vigorous fermentation will cause residual DMS to leave the beer through your airlock.

Under-Attenuation

Lastly, if there isn’t enough yeast then you can end up with an overworked, tired yeast colony that just ‘gives up’ before it’s finished leaving high residual sweetness and not enough alcohol. If you’ve made or had a homebrew that had a cloying sweetness or tasted like unfermented wort, there is a chance that there wasn’t enough yeast pitched (under-attenuation can also be caused by other factors).

So, how did I go about making the starter so that I can eliminate all of these unwanted flavors? It’s actually a lot easier than a lot of homebrewers believe, especially if you have the right equipment.

I use Briess Pilsen DME for all of my starters, and I let software tell me what size starter to make. For this Helles Bock, I needed a 4.2 liter starter according to beersmith. I keep things fairly simple; for all of my starters I use 100g of DME per liter, so for the starter pictured below I went with 4.5 liters and added 450g of DME to my flask with a half teaspoon of nutrient, then added RO water to the 4.5L mark and placed on my stove. Once it was heated beyond pasteurization temps (I got this one to 170F, not enough headspace to try for a true boil, but it kills all the baddies) I pulled it and placed it into my sink with cool water, letting it cool to room temp before pitching my pack of yeast.

4.5 Liter starter in a 5L flask. Note: This is a lab grade flask, and a gas stove. DO NOT HEAT FLASKS ON ELECTRIC STOVES.

You can see the hot break from the DME as it heats up.

After fermentation activity slowed, I cold crashed the starter and decanted all but about .5L. I swirled up the yeast cake and pitched all of that lovely yeast into 6 gallons of Helles Bock wort.

A scant 24 hours after pitching the yeast, you can already see good yeast activity. Plenty of CO2 formation, and even some bits of krausen that are forming on top. Remember, this is lager yeast, and the fermentation at this point is being held at 50F. Without a starter, the top of this wort would have still been clear for a while.

Making a starter doesn’t have to be complicated, and it can improve the quality of your beer drastically. Starters can help prevent or eliminate unwanted off-flavors, allowing your yeast to take hold of the fermentation quickly and effectively, giving you the refreshing brew that you want.