Cold-water lime pasteurisation

What it is

Lime raises the pH of the soaking water to 12 or 13, which kills most competitors, and oyster mycelium is then added to the drained straw¹. Cornell’s guide stresses using hydrated lime with a magnesium content under 10%¹.

As a starting point the guide adds 0.35 to 0.5 lb of lime per gallon of water, checks the pH with test strips and soaks the straw for 16 to 18 hours, no longer¹.

In a Northeast SARE farm trial, straw soaked 16 hours at pH 12–13 gave on average 12% more mushrooms than hot-water pasteurisation, and fully contaminated bags were much more common with fermentation and wood-ash treatments than with lime or heat². That is one farm’s trial; Cornell’s own table lists lime as "moderately reliable"¹.

What it suits

Oyster mushrooms on straw¹.

Species notes are on the species page; for the mushrooms themselves, see Ohio Gourmet Mushrooms.

Equipment

• Hydrated lime with magnesium under 10%¹
• A barrel or tote big enough to submerge the straw
• pH test strips
• Gloves and eye protection
• Mesh bags or a basket to lift the straw out
• Oyster spawn and bags or buckets

Time to first harvest

About 3–4 weeks to colonise, then fruiting. In the SARE trial, lime-treated bags incubated for 3 to 4 weeks before moving to fruit². Cornell gives 14 to 28 days of incubation for oysters on straw¹.

Contamination and other risks

• Lime with too much magnesium, which Cornell calls critical to avoid¹.
• Soaking longer than 18 hours¹.
• The same green moulds and insects as hot-water straw³¹.

Steps, in overview

1. Mix. Stir hydrated lime into water at roughly 0.35–0.5 lb per gallon and check that the pH reads 12 or more¹.
2. Soak. Submerge the straw for 16–18 hours¹.
3. Drain. Lift out and drain; the SARE trial drained for 20 minutes².
4. Spawn and pack. Mix in oyster spawn and pack bags or buckets firmly.
5. Neutralise the water. Bring the pH down with a pH-down product before disposal¹.

Common mistakes

• Buying dolomitic or garden lime instead of low-magnesium hydrated lime¹.
• Skipping the pH check¹.
• Pouring the high-pH water out untreated¹.