Detailed Explanation of the Processing Technology of Fermented Almond Yogurt

(1) Product Features

The dried seeds of almonds -- bitter almonds -- are used as the main raw material, and a plant protein fermented milk beverage can be made through lactic acid bacteria fermentation. Lactic acid fermentation improves the special aroma of bitter almonds, making them more acceptable to consumers. Bitter almonds are rich in various unsaturated fatty acids, with a protein content of about 24%, and contain abundant vitamins and trace elements such as iron, giving them high nutritional value and health benefits.

(2) Main Raw and Auxiliary Materials

Bitter almonds, white granulated sugar, skim milk powder, acid-resistant sodium carboxymethyl cellulose, Lactobacillus bulgaricus and Streptococcus thermophilus cultures.

(3) Process Flow

Almonds -> peeling -> soaking for detoxification -> pulping -> filtering -> almond milk -> mixing and blending -> homogenization -> sterilization -> cooling -> inoculation -> fermentation -> post-ripening -> finished product

(4) Explanation of Key Operation Points

(1) Preparation of Starter Culture

① Weigh 0.1 g of dry powder (a mixed bacterial powder of Lactobacillus bulgaricus and Streptococcus thermophilus at 1:1) and dissolve it in 5 mL of 0.9% peptone solution.

② Pipette 0.5 mL of the dissolved dry powder peptone solution into a slant medium. Preparation of the slant subculture medium: dissolve 100 g of skim milk powder in 1000 mL of distilled water, and sterilize at 121°C for 20 minutes; add 25-30 g of agar and 2.5 g of yeast extract to 300 mL of distilled water, boil to dissolve, and sterilize at 121°C for 20 minutes; while hot, mix the two liquids under aseptic conditions to prepare slants (solution volume of 15 mL).

③ Place a lit candle in a desiccator, put in the inoculated slants without allowing air leakage, and culture in a constant-temperature incubator at 37°C for 18-24 hours.

④ Pick the bacteria from the slants into milk test tube medium and culture at 37°C for 18-24 hours.

Preparation of milk test tube medium: dissolve 120 g of skim milk powder in 1000 mL of distilled water, place 20 mL in a test tube, hold at 95°C for 20 minutes, and sterilize intermittently in a water bath 3 times.

⑤ Culture acclimatization: inoculate 4% of the culture from the milk test tube medium into almond juice test tube medium and culture at 41°C for 8-12 hours.

a. Preparation of almond juice test tube medium: mix 20 mL of almond milk (pulped, passed through a 180-mesh sieve, with 10 times the amount of water added) with 80 mL of milk (milk powder:water = 1:7), place 20 mL in a test tube, hold at 95°C for 20 minutes, and sterilize intermittently in a water bath 3 times.

b. Erlenmeyer flask scale-up culture: take 4% of the culture from the above medium into an Erlenmeyer flask for culture and culture at 41°C for 8 hours.

c. Preparation of Erlenmeyer flask medium: mix 600 mL of almond juice (same as above) with 400 mL of milk (same as above), pour into an Erlenmeyer flask, hold at 95°C for 20 minutes, and sterilize intermittently in a water bath 3 times. After scale-up culture, it is a directly usable almond milk starter culture.

(2) Preparation of Fermented Almond Milk Beverage

① Almond peeling: boil the almonds in a 2% sodium hydroxide solution for 3-4 minutes, then peel with a peeling machine, and manually select almonds that meet the quality requirements.

② Soaking for detoxification: soak in clean water for 20-24 hours, changing the water 2-3 times during this period.

③ Mixing and blending: the ratio of almonds (wet weight) to milk powder is 100:10, the amount of sucrose used is 8%, sodium carboxymethyl cellulose:propylene glycol alginate = 2:1, and the total amount of the two is 0.2%-0.3%. First mix and dissolve the milk powder, white granulated sugar, and stabilizer, then add them to the slurry when the almond milk has heated up to 70°C, stir evenly, and keep warm for 10 minutes. After blending, make the final slurry solid content 8%-12%.

④ Homogenization: homogenize while hot at a pressure of 35-40 MPa.

⑤ Sterilization: use water bath sterilization at 95°C for 20 minutes.

⑥ Cooling: cool to 40-45°C.

⑦ Inoculation: add the starter culture that has been activated and scale-up cultured, inoculating at 4%.

⑧ Fermentation: ferment under oxygen-deficient conditions in a 41±1°C greenhouse (or incubator). Generally, remove when the acidity reaches 50-70°T (titratable acidity) and the pH value is <=4.2.

⑨ Post-ripening: store in a 4°C cold storage for 12 hours.