Yeast - Let's Get Started!

HBS Blogger Chris Corcoran

If you have read any of my previous posts you know I stress two points over and over, temperature control and yeast health. Temperature control allows you to craft the flavors you want. Healthy yeast allows you to fully ferment the beer, avoid off flavors, and lower the chance for infections. You’ve spent several hours crafting what may be the best beer you’ve ever made, why chance ruining that?

Any pitch of yeast can benefit from a starter but certain circumstances require it. At its most basic a starter “proofs” the yeast, shows you that it is viable and active. In the larger scheme of things, yeast starters grow more yeast and reduce the need for buying more packets or vials. In addition yeast starters will allow you to ferment beers with higher alcohol, beers fermenting at lower temperatures, or recycle old yeast rather than toss it out.

The process is very simple. You can use the yeast pitching calculator at www.mrmalty.com to determine the size of the starter needed. Combine 10g (grams) dry malt extract for each milliliter (1mL) of water. As an example, you will need 1000g (1000 grams = 1Kg) of DME (dry malt extract, the lighter colored the better) for a 100mL starter. If available use an Erlenmeyer flask. This type of flask allows you to boil on the stove and chill in an ice bath without increased risk of breaking the glass (it is really a high tech plastic).

Combine the DME and water in the flask and boil for 15 minutes to sanitize everything. There is no need to add hops. Hops are used to balance sweetness. Since we won’t be drinking this it is unneeded. Some friends of mine do add hops, mainly because that is the way they have always done it. Hops impede yeast growth a bit. In very hoppy beers you should do a yeast starter to circumvent this. In this case, when I've seen friends add hops to a starter, they add one or two pellets. The amount is small enough that it wouldn't really hurt the yeast, but it would contribute to piece of mind.

As you near a boil, be careful. The shape of the flask contributes to an easy boil over. Once you achieve a consistent boil (rolling but not high), loosely cover the top with tin foil. The 15 minute boil will sanitize everything. An air lock is not needed. We want a lot of oxygen to get into solution as this will promote yeast growth. Loose tin foil over the top will keep dust and bugs out of the starter and this is all that we really need to do.

After boiling the solution for 15 minutes use an ice bath to cool to room temperature. Once you reach room temperature add your yeast and aerate well. The key from here on out is aeration. Oxygen plus yeast plus sugar equals more and more healthy yeast.

Set the starter out on the counter and leave it at room temperature. As long as your room isn’t uncomfortably hot or cold it won’t be a problem. We aren’t overly concerned with temp control here because we aren’t fermenting beer. The liquid will get removed at the end leaving behind good healthy yeast. On the high end, we don’t want overly warm temps (80’s or 90’s) because we don’t want the yeast to be deformed, which could produce off flavors when we ferment beer with it.

Over the course of the next few days the starter will start to Krausen, that is foam or bubble. Once it’s done the starter is almost ready to go. Chill the starter in the fridge for 24 hours to help the yeast quickly drop out of solution. If you have the time you can wait instead. The yeast will drop out naturally over the course of a week or two. Pour off most of the liquid leaving enough behind to swirl the yeast back into solution. The yeast starter is now ready to pitch into your beer!

A stir plate can assist hugely in this process. It increases the amount of O2 in suspension which means more yeast. If you don’t have one available to you, you can use the “shake when you walk by” method. This is just what it sounds like. Each time you walk by the starter, shake it up!

One last note, if you are making a very large starter, say 5000mL (5L) for a high gravity lager, you will want to add a pinch of yeast nutrient. For normal starters this isn’t really needed. I add yeast nutrient to all my brews but only to my starters when they are either over 500mL or when the yeast is over a year old.

Recently I made a starter from a two year old vial of yeast. There was no visible activity for 4 days, but after these few days there was a layer of white healthy yeast at the bottom of the flask. The batch was a small 200mL starter. Next I made another 500mL starter with this yeast and then pitched it into an average gravity beer (average gravity being between 1.050 and 1.070). The beer fermented out nicely.