Advantages of Using Dry Yeast
Dry yeast has a lot of advantages over liquid yeast. It is cheap and readily available. If stored cool and dry, after 2 years the cells still have a viability over 90%. The form factor is small and one packet contains around 230 Billion cells. That is more than enough for a 5 gallon batch. The biggest drawback is limited variety. Not all yeast strains are available in dried form. I am still waiting for a hefeweizen dry yeast with the same qualities like their liquid counterparts. In conclusion, if you are brewing ales or lagers where good quality dried strains are available, dry yeast clearly has the edge; therefore, I would recommend to always keep a few packets in the fridge.
Why Rehydrate Dry Yeast?
It is possible and it certainly works to sprinkle the yeast directly onto the wort, but there are negative side effects. A lot of cells are going to die in the process. Some of them start unhealthy and many are stressed. There is a risk of mutants and a lot of dead cells are going to end up in the wort. In addition, to get to the correct cell count you have to use about double the amount of dry yeast. This is money that could be invested for better things, like more malt and hops. Correctly rehydrating dry yeast is important. Yes, this adds a few steps to your brew day, but remember that it is the yeast and not the brewer who makes the beer.
How to Correctly Rehydrate Dry Yeast
Here is how to rehydrate one packet or 11.5g of dry yeast. You can scale the numbers accordingly to your quantities.
Things you need:
Microwaveable container (best with lid): This could be a drinking glass, mason jar, or Pyrex measuring glass. Microwave safe plastic should also work well. For one packet of yeast you need around 2 cup (~475 ml) of volume.
Microwave: Any microwave is ok, it just needs to be big enough for your container.
Thermometer: You can take your default brewing thermometer. A quick measurement and long probe are beneficial.
Yeast rehydration nutrient: Go Ferm Protect is the standard - you will need 1.25 grams per gram of dry yeast (13.75g for the 11.5g yeast packet).
Water: Bottled spring water is best; however, whatever water you normally use for brewing should probably suffice (the small amount of chlorine found in tap water has not been shown to have a negative impact here. You will need 20X the weight of Go Ferm as your water in ml (275 ml or just under 1 ¼ cup for you 11.5g yeast packet).
Timing
Start about 2 hours before pitching. This is about the time it takes to naturally cool 1 cup (236ml) of boiling water to 95F (35C). The timing could be different for you, make a trial run before your brew day. Starting earlier is better than later, you can always reheat the water if it gets too cold. At the same time you should also take the yeast packet out of the refrigerator.
Measuring
Take 20x times the amount of water as the amount of Go Ferm you will be using when you rehydrate your yeast. For a normal 11.5g packet, you would use 13.75g of Go Ferm, so this would require 275ml of water (just under 1 ¼ cup). If your water source is good, use normal tap water if not you can use bottled spring water. Demineralized or distilled Water is not ideal. Put that water into your microwaveable container. About half of the container should still be empty, that way it is easier to mix later.
Boiling
Warning: If your container has a lid, leave it open for the steam to escape and never put metal into the microwave. Place the half filled container into the microwave. Nuke it until the water boils. Turn off the microwave and leave your container in there to slowly cool down.
Temperature Check
30 - 60min before you want to pitch the yeast take the container out of the microwave. Swirl the water around to even the temperature. Sanitize your thermometer probe, and then check the temperature. The water temperature must be between 95F (35C) and 105F (40C). This is very important. Dry yeast likes to be rehydrated very warm. If the water is already too cold, you can heat it up again by nuking it for a few seconds in the microwave. Don't forget to swirl before you take a new measurement.
Soaking
Once the water has cooled to the proper temp add the Go Ferm, and then swirl with something sanitized (I use the sanitized probe of my thermometer) until completely dissolved. Next open the packet and sprinkle all the yeast on top of the water. Don't stir it yet. Just close your container or put it back into the microwave (without turning it on). If you don't have a lid, you can cover it with some aluminum foil.
If you have a sealable container, you can put it into the refrigerator while rehydrating. I do this when preparing yeast for a lager. The temperature will go down quicker and the cells will be better acclimatized when it's time for pitching.
Mixing and Pitching
After 15min - 20min, the yeast should be soaked. Now you can swirl it around or mix it, again, with something sanitized. The yeast is now ready to pitch. There is a tradeoff between the time you wait and the temperature of the prepared yeast. It should be as close to the wort temperature as possible to avoid temperature shock. Don't leave the yeast sitting around for more than 1 hour. The cells will start to use up their glycogen reserves. If your wort is no more than 10F (7C) colder than your yeast, it should be good to pitch.
Final words
So this is how you correctly rehydrate dry yeast. Remember to always use proper sanitization techniques when working with yeast and wort at low temperatures. Take care when handling hot liquids. I hope you will save a lot of money and yeast cells by adopting this technique. Thank you for reading and feel free to add any comments below.
I personally feel that rehydrating dry yeast is good to do if you can work it into the brew day. If for the only reason is that it "proofs" the yeast and you will almost always have a successful pitch if the yeast "proofs" first. Its is one less thing to worry about at that point.
