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Grainfather Blog - Week 130: Yeast Series - Rehydration

By Grainfather - All Grain Brewing 29/09/2017 13:49 Comments

Yeast Rehydration

Yeast is arguably the most important ingredient in beer, without it we would be left with sugary bitter wort. The next few weeks will look into some of the major topics when it comes to homebrewers working with yeast. 


Dry yeast is often added directly on top of the wort in the fermenter by home brewers. This method is ideal for beginners and when you are not confident with sanitation practices. It is easy to kill the yeast at high temperature and can also allow for the introduction of wild yeasts. However when sprinkling dry yeast directly to the top of the wort about half of the yeast cells are killed, which may put a strain on fermentation and producing off flavours.

Most manufacturers will have a specific process for the rehydration of their yeast however here is a basic overview of the process;

  1. Items you will need and the process:
    1. Sanitiser
    2. 250 ml (8 fl oz)container
    3. Larger container for water bath
    4. Thermometer
    5. Sanitised non chlorinated water 200 ml (6.7 fl oz) (fresh filtered water or by boiling tap water for 7 mins)
    6. Aluminium foil
    7. Allow the yeast to warm to room temperature
    8. In a sanitised container prepare a small amount (10 ml/g of yeast) of sanitised non chlorinated water use a water bath of either boiled or cold water to get your yeast water to 30 - 400C (86 -  104°F) for Ales and 15 - 25°C (59 – 77°F) for lager yeasts
    9. Sprinkle dry yeast over the top of the water trying to avoid any large dry clumps let sit for 15 mins loosely covered with aluminium foil to avoid foreign matter and wild yeast falling in the yeast, then stir gently
    10. Gently stir again to form a cream then let sit for another 5 mins covered
    11. Ensure the temperature of the cream is within 80C (46°F) of your wort
    12. Pitch the cream into the fermenter ideally as soon as possible

Next week we will be discussing ‘starters’ with dried or liquid yeast. 

Post Comments

Grainfather Recipes

posted on 24/10/2017 08:04
Hi Matt,
First we want to re-hydrate the cells to ensure they are in the right condition to do work, but as soon as this occurs they are happy to do this work. The reason to add sugar in a starter application is to provide food for the yeast to so that they can multiply. By adding sugar in the re-hydration will have a similar effect as pitching the dry yeast directly into the wort

matt dunn

posted on 21/10/2017 06:15
Should you not add a tsp of sugar to this to get them activated before pitching them?

Grainfather Recipes

posted on 18/10/2017 08:11
Yeast – The practical guide to beer fermentation by Chis White and Jamil Zainasheff p146

This is mainly due the concentration gradient of the sugars in liquid. With rehydrated yeast their cell walls are in better shape to handle this concentration gradient but with dry yeast being added directly to this the cell walls of the cells are not in the optimum condition and therefore this concentration gradient kills a lot of the cells on contact. This is not to say that a packet of dry yeast added to the top of a fermenter will not work or produce good beer but there is a higher chance for issues to arise.

Jim Harvey

posted on 18/10/2017 08:05
"However when sprinkling dry yeast directly to the top of the wort about half of the yeast cells are killed"

Where are you getting this information from? It is hard for me to believe this considering my extensive experience using dry yeast exclusively.

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