Grape juice-agar medium

Reagents

Agar

Concentrated (3:1) grape juice

Sucrose

p-Hydroxybenzoic acid methyl ester (HAME, Sigma H 5501)

Equipment

Bunsen burner or hot plate (see Step 2)

Plastic bags

Styrofoam trays, 25.7 × 20.6 cm

To prepare 1 liter:

• 1. Add 20 g of agar to 750 ml of H₂O and autoclave to melt the agar.

• 2. Combine 250 ml of concentrated (3:1) grape juice, 6.25 g of sucrose, and 1.5 g of HAME. Bring the mixture to a boil over a Bunsen burner or a hot plate; stir to dissolve the HAME and to prevent burning. Remove the mixture from the heat once the HAME has dissolved.

• 3. Mix the agar and grape juice solutions together once each has cooled to 70ºC. Let the grape juice-agar solution sit, allowing bubbles to rise.

• 4. Pour the medium into Styrofoam trays, forming a thin smooth layer (150 ml per 25.7 × 20.6-cm Styrofoam tray).

• 5. Once the agar has solidified, store medium at 4ºC. Store the Styrofoam trays in plastic bags, taking care to not gouge the surface of the medium.