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When it comes to yeast I often see three different descriptors used:

  • active vs. dormant
  • needs to be rehydrated vs. doesn't
  • dry vs liquid/wet

As a newbie, my immediate inclination is to associate dry (powdery) yeast with dormant, however almost all "dry" yeast seems to also be billed as dry active yeast (DAY). Some yeasts need to be rehydrated whereas other yeast do not.

Can someone help me sort all these monikers out in my head? Or is any combination thereof possible? Meaning, could I find an active, non-dormant, dry yeast that doesn't need to be rehydrated? As well as any other combination?

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  • Can you give (commercial) examples where active and dormant terms are used?
    – chthon
    Oct 14 at 5:50
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Active and dormant are part of the yeast cycle and has nothing to do with sales or packaging.

Yeast becomes active when it detects that is in a nutritious environment. Then it starts fermenting. When all nutrients (sugars) have been used up, then the yeast becomes dormant, and then it flocculates out of the solution.

When it is liquid dormant, it can be dried, and then you get dry yeast. Liquid packages of yeast are also dormant.

I have at home trappist yeasts in liquid form in my fridge, these are all dormant.

I think "Dry Active Yeast" has more to do with marketing than technical merits. I even found a reference saying "active dry yeast is a dormant yeast". But apparently this term is more used for baking yeast.

Rehydrating or not, some producers recommend it, and others don't. That is more to make the life of the hobby homebrewer simpler. I won't go into the pros or cons, because it is still being debated to death every now and then on most homebrew forums.

Answers to followup questions:

a) All dry yeasts can be hydrated or pitched dry. What is being debated is if it makes a difference in:

  • quality of the beer
  • viability of the yeast

b) Yes, dry yeast stores better than liquid yeast. Viability of liquid yeast drops quickly. I have used dry yeast of more than two years old, stored in the fridge, without problems. I have used baking yeast of five years old, stored in the fridge, without problems for making bread.

c) Yes, there are less beer yeasts available in dry form, than liquid yeasts. However, (small) commercial brewing will probably use a dry yeast that best fits their product. It is much cheaper than buying liquid yeast, and one doesn't need laboratory equipment to create starters. And liquid starters tend to grow big, which means investing in laboratory material, making wort for starters, time to grow starters etc...

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  • Thanks @chthon (+1) a few followup questions if you don't mind: (a) are you saying that all dry yeasts need to be rehydrated, or are you saying that some dry yeasts do and other dry yeasts don't, and that this is what is being heavily debated? (b) does dry yeast store "better" (more amenable and tolerant of temperature and humidity swings, etc.) than liquid? Otherwise what would be its benefits over liquid? Oct 14 at 11:44
  • And (c) I hear 2 conflicting things about dry yeast: on one hand I hear there are less strains of it available than in liquid form, and on the other hand I hear that commercial breweries strictly use large bricks of dry yeast. Which doesn't make sense, I would think commercial breweries would choose a format (dry vs liquid) that had the most options available to them, no? Oct 14 at 11:44
  • @hotmeatballsoup: w.r.t. to big commercial brewers, they will also have very specialised equipment (reactors) to grow and multiply their own house yeasts, and keep it in shape.
    – chthon
    Oct 14 at 13:45
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In addition to the information already provided above: the term "active" yeast (as in Active Dry Yeast) primarily serves to distinguish between "live" yeast suitable for fermentation and inactivated (dead) yeast only suitable for health food supplements, yeast extract production for the food industry and the like. Active yeast is sold in a dormant state (since it will only come out of its dormant state when pitched into a yeast starter or fermenter). The distinction between dry yeast and sludge has already been discussed above; this makes no difference to the yeast being described as "active".

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