Beer School

Brew Day Hour 4: Pitch the Yeast

updated May 1, 2019
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(Image credit: Melissa Ryan)
(Image credit: Henry Chen)
  • Today’s topic: Detailed look at cooling the wort and adding the yeast.
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After mashing the grains, making our wort, and then adding the hops, there’s really only one thing left to do in the beer-making process: add the yeast. This is the final leg of the brew day — after this, you get to walk away and let the beer bubble and ferment on its own for a little while.

Besides going over the actual process for mixing the yeast into the wort, today we’ll also tackle the oh-so-thrilling topic of sanitation.

(Image credit: Melissa Ryan)

Talk Like a Brewer

  • Pitch the yeast: Pouring the yeast into the cooled wort.
  • Gravity reading: A measure of the sugars in the beer, taken using a hydrometer, used to calculate the alcohol content of the finished beer.
  • Original gravity: The gravity reading of the wort before fermentation begins. Typical readings are around 1.050 for homebrews with a 5% projected ABV.
(Image credit: Henry Chen)

What Happens During This Hour?

The goal of this final hour of the brew day is to cool down the wort as quickly as possible so we can add the yeast and kick off fermentation — we want to cool the wort to room temperature (at least 75°F) in 20 to 30 minutes.

For our small, 1-gallon batches, the easiest and quickest way to do this is to put the pot of hot wort in the kitchen sink and fill the sink with water and ice cubes. Change out the water as it warms and add more ice cubes as needed (it’s handy to pick up a bag of party ice from the store if you don’t usually keep a lot of ice in your freezer).

While the wort is chilling, start sanitizing all the equipment you’ll need for this stage: the 2-gallon bucket you’ll use for fermentation, its lid, the airlock, a small strainer, a measuring cup, the hydrometer, the hydrometer tube, and a whisk. I find it easiest to fill the fermentation bucket with sanitizing solution and put all the equipment inside. Most sanitizers need to be diluted in a specific amount of water and require a specific amount of contact time with the equipment to do their sanitizing job — read the directions on your sanitizer carefully so you know how to use your sanitizer.

When your equipment is sanitized, you can lay everything out on clean kitchen towels until you need it. Before pouring it out, pour a little of the sanitizer into a spare pot or other container in case you need to quickly re-sanitize anything later on.

Once the wort is cool and your equipment is sanitized, a few things happen in a row: First, transfer the wort to the sanitized fermentation bucket, pouring it through a small strainer to filter out as much hop sediment and leftover grit from the mash as you can. Next, scoop out a little of the wort and get a gravity reading with your hydrometer (more on that below). Then, add the yeast to the wort — called “pitching the yeast” in brewing terms. Yeast like some oxygen at the start of fermentation, so whisk the wort vigorously with the sanitized whisk until the wort looks frothy.

Last but not least, snap the sanitized lid on the bucket and insert a water-filled airlock into the hole in the lid. That airlock is the gatekeeper between your beer and the outside world. It prevents bacteria, wild yeast, and dust from getting inside to infect your beer, and it also lets the carbon dioxide created by the fermenting yeast escape from the bucket (otherwise too much pressure would build up inside the bucket and the lid would pop off). Be sure to fill your airlock up to its “fill line” with water, sanitizing solution, or vodka (any of these will work) up to the “fill line.”

Yeast pitched, lid on, airlock in — your beer is off and running, and your brew day is officially done! Well, almost … if your kitchen looks anything like mine after a brew day, you’ll have some cleanup to do!

(Image credit: Melissa Ryan)

Why Is Cooling the Wort Important?

Yeast are sensitive little creatures. Yeast die above 110°F, go dormant below 60°F, and are happiest at 65°F to 75°F. In an ideal world, you’d cool your beer wort below 70°F, but in a practical, homebrewing world (emphasis on home), you really just need to get the wort cooled to room temperature.

Cooling the wort quickly is also important (within 20 to 30 minutes is ideal), but if it does end up taking you longer, it’s not the end of the world — or your beer. The longer it takes to cool the wort, the greater chance that an unwelcome strain of bacteria or wild yeast could find its way into your wort and infect your beer. However, as long as you’re doing your best to cool the wort and keep everything sanitized, the likelihood of this happening is pretty small.

Why Take a Hydrometer Reading?

A hydrometer is a very handy tool to help calculate the alcohol level in your beer. I’ll spare you the full science geek explanation for the moment (we’ll dig into that in a future lesson). For now, just know that the hydrometer helps measure the amount of sugar in your beer. By taking one reading now and another before you bottle, you know how much sugar has been consumed by the yeast during fermentation, and therefore, how much alcohol has been created. This first reading is called the “original gravity” and the second reading is called the “final gravity.”

To get this first “original gravity” reading, fill your sanitized hydrometer tube three-quarters full of cooled wort and insert the sanitized hydrometer. The hydrometer will float in the liquid; look at where the surface of the liquid intersects with the measurements on the hydrometer and record that number. It will typically be around 1.050 for most homebrews of average alcohol level. Most hydrometers are calculated to 60°F, so if your wort is warmer, adjust the reading as needed according to the instructions that came with the hydrometer.

If this feels intimidating or tedious to you, you can skip this step. It’s not crucial to actually making or fermenting the beer. You won’t know the exact alcohol level in your finished beer, but if you’re OK with a bit of mystery in your life, then that’s just fine.

Anything that comes into contact with the chilled wort needs to be sanitized. (Image credit: Melissa Ryan)

Why Is Sanitation Important?

From the moment you take the wort off the stove and start cooling it down, anything that comes into contact with the wort needs to be sanitized. This includes buckets and jugs, stirring spoons and measuring cups, and tubes and bottles. Sanitizing is definitely the boring, un-glamorous side of beer brewing, but it’s necessary.

We need to sanitize because errant bacteria and wild yeast would absolutely love to find a cozy home in our freshly made beer, and we can’t let that happen. At best, this bacteria or yeast would make beer taste sour; at worst, it would make the beer goopy, smell like a frat house the morning after a party, and taste even worse. (Hint: Not awesome.) Sanitizing our equipment means that the only thing taking up residence in our beer is the yeast that we put there intentionally.

There are all sorts of sanitizers you can use, from household bleach to fancy sanitizers at homebrew stores. Personally, I like to use StarSan, which is food-grade (so you don’t have to rinse it off), sanitizes equipment in about a minute, won’t add any weird flavors to your beer, and can be saved and reused for a few batches. (Heads up, StarSan is also very foamy! It’s fine for some bubbles to cling to equipment or the insides of bottles — no need to wash away.) Whichever sanitizer you use, follow the dilution ratios carefully and pay attention to the recommended contact times for sanitation.

One last thing: Sanitizing is not the same as cleaning — cleaning removes gunk and large particles; sanitizing kills microscopic bacteria. Both are necessary, but one can’t replace the other. Make sure all your equipment has been thoroughly cleaned before you sanitize.

(Image credit: Melissa Ryan)
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Place the pot of wort in an ice water bath: As soon as the hop boil is complete, transfer the pot of hot wort to your kitchen sink. Place the stopper in the sink and fill it up with cold tap water — be careful not to splash water in the pot. Add as much ice as you have to make a cold ice bath. (Image credit: Melissa Ryan)

What to Do: Cooling the Wort & Pitching the Yeast

These general directions apply to any batch of beer you brew (though the process is slightly different for larger, 5-gallon batches and requires some different equipment).

Flip through the slideshow above for step-by-step photographs of each step of the hop boil.

Before you begin:

If you think ahead and have the space in your freezer, pick up a big bag of party ice from the grocery store or make a few batches of ice cubes and keep them in zip-top bags in your freezer. You can definitely cool down the wort with just the ice you have, but a big bag of it makes everything go more quickly and efficiently.

  1. Place the pot of wort in an ice water bath: As soon as the hop boil is complete, transfer the pot of hot wort to your kitchen sink. Place the stopper in the sink and fill it up with cold tap water — be careful not to splash water in the pot. Add as much ice as you have to make a cold ice bath.
  2. Cool the wort to at least 75°F in 20 to 30 minutes: Change out the ice water as the ice melts and the water becomes warm. (If you had a lot of ice, you might not need to do this.) Occasionally, stir the wort with a sanitized spoon and check the temperature with a sanitized thermometer (see next step).
  3. Meanwhile, sanitize all your equipment: Fill your fermentation bucket with sanitizer and place its lid, the airlock, a small strainer, a measuring cup, the hydrometer, the hydrometer tube, and a whisk inside. Once sanitized (following the directions for your sanitizer), lay the equipment on clean dish towels. Save a little sanitizer solution in a separate container to use for any last-minute sanitizing (or re-sanitizing!) before pouring it out.
  4. Transfer the cooled wort to the fermentation bucket: Place a sanitized strainer over the sanitized fermentation bucket and pour the cooled wort through the strainer into the bucket. This filters out hop sediment and other solids.
  5. Check the volume of your wort: Check the volume of your wort against the measurement markings on the side of the bucket. If you’re a little under a gallon, add tap water or filtered water as needed to make a gallon. (As long as your tap water is safe to drink, it’s sterile enough that there’s not much risk of introducing bad bacteria.) If your volume is a little over, don’t worry about it — either you started off the hop boil with slightly more wort than you needed or your wort wasn’t at a full boil for the full time. Your beer will be fine, but may have a slightly lower alcohol level than predicted.
  6. Take a hydrometer reading: Scoop out a little wort with the sanitized measuring cup and pour it into the sanitized hydrometer tube. Float a sanitized hydrometer in the liquid. Look at where the liquid hits the hydrometer and record the number (usually around 1.050), adjusting for temperature if necessary. Pour the wort from the hydrometer tube back into the bucket.
  7. Add the yeast to the wort: Pour the yeast into the wort. For these small 1-gallon batches, you only need to use half a package of yeast; the rest can be stored in a sterilized container in the fridge and used for another batch.
  8. Aerate the wort: The yeast need a little oxygen to get going, so vigorously whisk the wort with a sanitized whisk until it’s quite frothy.
  9. Snap on the lid: Make sure the lid is completely sealed all the way around. It should fit tightly to the bucket and won’t be very easy to remove.
  10. Add the airlock: Fill your sanitized airlock up to the “fill line” with water, sanitizer, or vodka. For 3-piece airlocks, insert the floater and cap; for bubbler airlocks, place the cap on top. Insert the airlock into the hole in the top of the lid. It should fit snugly with no gaps around the sides.
  11. Place the bucket somewhere out of the way and out of direct sunlight: You’re done! Now it’s up to the yeast to do their job and get fermentation going! Stash your bucket of wort somewhere out of the way and out of direct sunlight (like a closet, basement shelf, or behind the couch; you can throw a blanket over it if your apartment is sunny), but keep it somewhere you can keep an eye on it and make sure everything looks okay.
  12. Clean up the kitchen: Make this step a little happier for yourself and pour a beer while you’re scrubbing down the sticky counters.

In the next 24 hours, you should start seeing bubbles pop up through the airlock. This is a sure sign that fermentation is off and running. We’ll talk about what’s happening in the bucket and what to do if you don’t see any signs of fermentation in the next few lessons.

(Image credit: Melissa Ryan)

Pitching the Yeast: Troubleshooting

My wort is taking forever to cool down!

It’s OK! Cooling it in 30 minutes is ideal, but if it’s taking longer, everything should be fine. Just be extra careful with all your sanitation.

I’m not sure if my sanitizer is actually sanitizing, or if I’m doing it correctly.

I find this tricky, too. Sanitized equipment doesn’t look different, and there’s no magic iPhone app that will confirm that sanitization has happened. You just have to trust it. Read the directions for your sanitizer carefully and do the best you can.

I ended up with under a gallon of wort.

No problem — either you started off the hop boil with a little less wort than called for or your hop boil was especially vigorous. Just top off the wort with tap water or filtered water. As long as your tap water is safe to drink, then it is sterile enough that we don’t need to be worried about bad bacteria or anything else.

I ended up with more than a gallon of wort.

No problem — either you started off the hop boil with a little more wort than called for or your hop boil was a little less than vigorous. Your beer will still ferment just fine and taste good, but the alcohol level might be a little lower.

I don’t know if I’m using the hydrometer correctly.

This is not a crucial part of beer brewing. It’s handy and fun to have an idea of the alcohol level in your beer, but you can definitely skip this if it’s stressing you out. Also, if your reading is off by a degree or two, it won’t throw off the final calculation by that much. Do your best here and don’t let it keep you up at night.

I forgot to take my liquid yeast out of the fridge, and/or I forgot to activate it.

Ideally, you want the yeast and the wort to be about the same temperature — room temperature. Dry yeast can be used straight from the fridge, but liquid yeast needs some time to warm up. If you forgot to take it out of the fridge at the beginning of your brew day, take it out now and put it in a bowl of warm water, activating it if necessary (check the package directions). In the meantime, cover your wort with the lid to keep it protected.

I can’t figure out how to use my airlock!

If it’s an S-shaped bubbler airlock, all you need to do is fill it with water up to the “fill line,” cap it, and insert it in the lid of your bucket. If it’s a 3-piece air lock, fill the main piece with water to the “fill line,” then drop the smaller, cup-like piece inside so it settles over the tube sticking up inside the airlock. Cap it and insert it into the lid of your bucket.

Brew Better Beer: A Companion to Beer School

(Image credit: Emma Christensen)

I love brewing beer so much, I wrote a book about it! Brew Better Beer (May 2015, Ten Speed Press) is a complementary guide to Beer School. Take a look for even more nerdy details about homebrewing, how to brew 5-gallon batches, and plenty of recipes for different beers.

→ Find it: Brew Better Beer by Emma Christensen

With The Kitchn’s Beer School, we’ll teach you how to brew your own beer at home — and brew it with confidence. In 20 lessons and 7 weekend assignments, we’ll get you set up with your own home brewery, walk you through your first brew day, show you how to bottle your beer, and then toast you on your first pint. Ready to brew your first beer? Join us!