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Yeast starters, stir plates and pitch rates

Yeast starter guide: when liquid yeast needs a starter, pitch rates for ales and lagers, making a starter with or without a stir plate, dry yeast doses.

Updated November 2026 · 7 min read

Yeast colonies growing on an agar plate
Photo: Rainis Venta, CC BY-SA 3.0, via Wikimedia Commons
The short version
  • Pitch rate is how many yeast cells you add per milliliter of wort per degree Plato. Common targets: about 0.75–1.0 million for ales and 1.5–2.0 million for lagers.
  • A single fresh liquid pack is often enough for an average-strength 5 gal ale. Stronger beers, lagers and older packs benefit from a starter.
  • The AHA rule of thumb for 5 gal: up to 1.048 one pack with no starter; 1.050–1.065 a 1 L starter; above 1.065 a 2 L starter.
  • Dry yeast doesn’t need a starter. Dose it by weight per the maker: US-05 is 50–80 g/hL, so one 11.5 g sachet covers a typical 5 gal ale.
  • A stir plate keeps yeast in suspension and grows more cells from the same starter volume.

A yeast starter is a small batch of wort that wakes up and multiplies liquid yeast before brew day. This yeast starter guide explains when you need one, how big it should be and how to make it, with or without a stir plate. The goal is simple: pitch enough healthy yeast that fermentation starts fast and finishes clean.

Pitch-rate numbers come from the American Homebrewers Association’s pitch-rate article and White and Zainasheff’s Yeast, the same sources behind our yeast pitch rate calculator. Dry yeast numbers come from the Fermentis and Lallemand sheets.

How much yeast do you need?

Cells needed = pitch rate × wort volume in mL × gravity in °Plato. Plato is roughly 259 − 259 / SG, so a 1.050 wort is about 12.3°P. White and Zainasheff use about 0.75 million cells per mL per °P for ales and 1.5 for lagers; the AHA article uses 1 million for ales and 1.5–2× that for lagers. The calculator shows both.

Scanning electron microscope image of budding Saccharomyces cerevisiae yeast cells
Budding yeast cells: a starter grows billions of them.Photo: Mogana Das Murtey and Patchamuthu Ramasamy, CC BY 3.0, via Wikimedia Commons

Billion cells needed for 5 gal (18.9 L) of ale

0.75 million cells/mL/°P (White & Zainasheff); °P ≈ 259 − 259/SG

OG 1.040: 141 B141 BOG 1.040OG 1.050: 175 B175 BOG 1.050OG 1.060: 208 B208 BOG 1.060OG 1.070: 241 B241 BOG 1.070
Source: White & Zainasheff, Yeast; AHA pitch rates (calculated)

A lager at 1.050 needs about twice the ale figure, roughly 350 billion cells, which is why lagers are the classic case for a big starter or several dry sachets. Liquid packs and vials are usually sold as about 100 billion cells at manufacture and lose viability as they age; the calculator uses an estimate of about 0.7% per day from the manufacture date.

AHA rule of thumb for a 5 gal (20 L) batch of ale

Original gravityLiquid yeastStarter
Up to 1.0481 package✓ Not needed
1.050–1.0651 package~ 1 L starter
Over 1.0651 package✗ 2 L starter (or more yeast)
Lagers, same gravity1.5–2× the ale rate✗ Larger starter or several packs

Source: AHA: Determining proper yeast pitch rates

Yeast pitch rate calculatorEnter batch size, gravity, yeast type and pack date to see cells needed and whether a starter helps.

Dry yeast: dose by weight, no starter

Dry yeast is packed with a large, stable cell count and enough reserves to start without growing first, so makers dose it by weight instead of by cell count. Lallemand cautions that calculators built for liquid yeast can lead you to over-pitch dry yeast.

Dry yeast by the maker’s numbers

YeastUseFermentation tempDoseAttenuation / toleranceRehydration
SafAle US-05
Fermentis		Ale (American)18–26°C (64.4–78.8°F)50–80 g/hL78–82%; not listed on the product pageOptional: ≥10× its weight of sterile water or boiled, hopped wort at 25–29°C (77–84°F), 15–30 min; or direct pitch at or above fermentation temperature
SafAle S-04
Fermentis		Ale (English)18–26°C (64.4–78.8°F)50–80 g/hL74–82%; 9–11% ABVOptional: ≥10× its weight of sterile water or boiled, hopped wort at 25–29°C (77–84°F), 15–30 min; or direct pitch at or above fermentation temperature
SafLager W-34/70
Fermentis		Lager12–18°C (53.6–64.4°F)80–120 g/hL80–84%; 9–11% ABVOptional: ≥10× its weight of sterile water or boiled, hopped wort at 15–25°C (59–77°F), 15–30 min; or direct pitch at or above fermentation temperature
LalBrew Nottingham
Lallemand		Ale (English)10–25°C (50–77°F)50–100 g/hL78–84%; 14% ABVDry pitching is the maker's preferred method (no significant difference vs rehydration, per Lallemand)
LalBrew Voss (kveik)
Lallemand		Ale (kveik)25–40°C (77–104°F)
Optimum 35–40°C (95–104°F) per Lallemand		50–100 g/hL76–82%; 12% ABVPer the sachet
Lalvin EC-1118
Lallemand		Wine, cider, mead10–30°C (50–86°F)25 g/hLFerments dry; 18% v/v (subject to conditions)35–40°C (95–104°F) water for 20 min with Go-Ferm Protect Evolution (30 g/hL), then temper to within 5–10°C of the must

Sources: Fermentis: SafAle US-05 product page; Fermentis: SafAle S-04 product page; Fermentis: SafLager W-34/70 product page; Lallemand: LalBrew Nottingham technical data sheet; Lallemand Brewing: LalBrew Voss Kveik Ale Yeast product page; Lallemand: Lalvin EC-1118 technical data sheet. 1 hL = 26.4 US gal, so 50 g/hL ≈ 1.9 g per gallon. Follow the sachet you buy; makers update their sheets.

Example: 5 gal is about 0.19 hL, so US-05 at 50–80 g/hL means about 9.5–15 g. One 11.5 g sachet sits inside that range for an average ale; use two for high-gravity beers. For lagers, Fermentis lists 80–120 g/hL for W-34/70, so two to three sachets for 5 gal is common.

Whether to rehydrate first is covered in rehydrate dry yeast or direct pitch.

How to make a yeast starter

A standard starter is a low-gravity wort around 1.035–1.040, made from dry malt extract and water. Many brewers use about 100 g of light DME per liter of finished starter, plus a pinch of yeast nutrient. Canned starter wort skips the boil.

  1. Plan 24–48 hours ahead

    A stirred starter needs about 18–24 hours to grow; give it time to settle if you want to decant.

  2. Mix and boil the wort

    Stir the DME into water, bring to a boil for about 10 minutes and add a drop of antifoam to prevent boil-over. Use a heat-safe borosilicate flask or a pot.

    Briess Golden Light Dry Malt Extract, 1 lbFermcap-S Foam Inhibitor, 2 oz
  3. Chill to pitching temperature

    Cool the flask in a cold-water bath to around room temperature, 65–72°F (18–22°C). Don’t shock hot glass in ice water.

  4. Sanitize and pitch

    Sanitize the flask mouth, stir bar, foil or foam stopper and the yeast pack. Pitch the yeast.

  5. Aerate or stir

    On a stir plate, spin the stir bar to make a small vortex. Without one, cover loosely with sanitized foil and swirl hard whenever you pass by.

  6. Crash and decant (optional)

    For larger starters, chill the starter in the fridge overnight so yeast settles, pour off most of the spent liquid, and pitch the slurry. Small starters can be pitched whole at high krausen.

Hot glass and gasBoil starter wort only in borosilicate lab glass rated for direct heat or in a pot; ordinary glass jars crack. Use heat-resistant gloves and expect sudden foaming. BYO warns against pure oxygen on starters unless you can control it precisely; a stir plate or swirling supplies enough air.Source: BYO: Oxygenation

Stir plate or no stir plate?

Starter methods compared

MethodCell growthEffortNotes
Simple starter, swirled by hand~ ModestSwirl oftenBetter than nothing for average beers
Shaken starter (shake vigorously at pitching)~ GoodOne good shakePopular low-gear option
Stir plate✓ Highest per literSet and leaveKeeps yeast suspended and degasses CO2
Step-up (two starters in sequence)✓ For very big pitchesTwo days or moreLagers and high-gravity beers

Source: White & Zainasheff, Yeast; AHA pitch rates

A stir plate is a small motor turning a magnet under the flask, which spins a stir bar inside. It earns its place if you brew lagers or big beers with liquid yeast often. If you mostly use dry yeast, skip it.

Yeast health matters as much as count

Healthy yeast needs fresh packs, careful handling and oxygen in the main wort. Liquid yeast is perishable; order it with an ice pack in warm months and keep it cold until the day before. Check the manufacture date, because viability falls with age. Dry yeast keeps much longer; Fermentis lists a 36-month shelf life for US-05 when stored as directed.

Wort oxygen is the other half: yeast uses it to build healthy cell membranes before fermenting. A good shake works for average beers; pure oxygen with a stone helps big beers and lagers. See wort aeration.

Reusing yeast from a previous batch

The yeast cake left in a fermenter holds far more cells than a fresh pack, which is why many brewers re-pitch it. Use slurry only from a clean, healthy fermentation of a similar or lighter beer, collect it into a sanitized jar, keep it cold and use it within a couple of weeks. A cup or so of thick slurry is plenty for a 5 gal ale; dumping a whole cake into a new batch over-pitches it. Lallemand notes that re-pitched dry yeast needs wort aeration, because the harvested cells have used up the reserves the drying process gave them. Stop re-pitching after a few generations, or sooner if flavors drift.

Mistakes to avoid

  • Making a starter for dry yeast. Not needed at normal gravities; follow the maker’s dose.
  • Starting too late. A starter made the night before brewing is still mostly lag time.
  • Too-strong starter wort. Stick to about 1.035–1.040.
  • Pitching a big starter’s whole volume into a light beer. The spent, oxidized starter beer can show; decant large starters.
  • Using pure oxygen on starters. Easy to overdo.
  • Ignoring the pack date. Old liquid yeast needs a bigger starter or a fresh pack.
  • Heating ordinary glass. Use borosilicate or a pot.
A ring of yeast and krausen residue on the inside of a glass fermenter
A ring of yeast and krausen marks the high point of fermentation.Photo: Daquella manera, CC0 1.0, via Flickr

Who needs a starter

  • Dry yeast brewers: no starter. Weigh the dose and pitch.
  • Liquid yeast, average ale, fresh pack: often none; check the calculator.
  • Liquid yeast for lagers or OG over about 1.065: a 1–2 L starter or more, ideally on a stir plate.
  • Rare strains you want to keep: starters plus careful harvesting, with strict sanitation.

For lager-specific temperatures and schedules, see the fermentation temperature guide.

Gear picks for this guide: best wort aeration and oxygenation kits and best dry yeast for IPA and pale ale.

VerdictUse the pitch-rate math or the AHA rule of thumb to decide: average-strength ales with fresh liquid yeast often need no starter, while lagers and strong beers do. Dry yeast never needs one at normal gravities; weigh it to the maker’s g/hL dose instead.
Yeast pitch rate calculatorYeast pitch rate calculator: cells needed for ales and lagers by volume and gravity, dry yeast grams from…Dilution and boil-off calculatorDilute wort to a target gravity, and work out pre-boil volume from your boil-off rate, boil time and losses,…

Questions

Do I need a yeast starter?
For dry yeast, no. For liquid yeast, it depends on gravity, batch size, beer type and pack age. The AHA guide for 5 gal ales: no starter up to 1.048, about 1 L for 1.050–1.065 and about 2 L above 1.065. Lagers need roughly 1.5–2 times more yeast.
How much yeast for 5 gallons?
About 175 billion cells for a 1.050 ale at 0.75 million cells/mL/°P, or one 11.5 g sachet of US-05 by the Fermentis dose of 50–80 g/hL.
How long before brewing should I make a starter?
24–48 hours. That allows 18–24 hours of growth plus time to chill and decant if you want.
Do I need a starter for dry yeast?
No. Makers dose dry yeast by weight and design it to be pitched directly or after rehydration. Lallemand warns liquid-yeast calculators can over-pitch dry yeast.
Is a stir plate worth it?
If you use liquid yeast often for lagers or strong beers, yes: it grows more cells per liter. If you mostly use dry yeast, you can skip it.
Can I pitch two packets of yeast?
Yes. Two dry sachets or two liquid packs are a simple way to reach a lager or high-gravity pitch rate without a starter.
What gravity should a yeast starter be?
About 1.035–1.040. Many brewers use roughly 100 g of light DME per liter of finished starter.

Sources

  1. AHA: Determining proper yeast pitch rates
  2. White & Zainasheff, Yeast: The Practical Guide to Beer Fermentation (Brewers Publications)
  3. Fermentis: SafAle US-05 product page
  4. Fermentis: SafLager W-34/70 product page
  5. Lallemand: LalBrew Nottingham technical data sheet
  6. BYO: Oxygenation