I was surprised to find the correlation between pH and yeast metabolism. When making all grain craft beer at home, pH was never much on an issue. pH always seemed to take care of itself and it has been debated if 5.2 pH buffer added to the strike water before the mash was more harmful than beneficial to the beer. I haven’t spent much time thinking about water chemistry.

pH isn’t of much concern for the all-grain beer homebrewer, but with sugar wash, it’s a different story.

My sugar washes were more times than not, sluggish. I was adding about 100 grams of yeast with no nutrient, relying on overpitching the yeast to make up for not adding nutrient. Believing that any amount of nutrient will negatively affect the final outcome.

I also think I ran into clearing issues because of the amount of yeast I was adding. My wash was always cloudy even if I used chitosan and kieselsol.

This time was different. I found a yeast, Red Star Premiere Rouge, that would work in my closets’ temperature range (24-26 degrees C) and that was recommended on the ADI forum for making a neutral.

Yeast Nutrient

I used Superfood as the yeast nutrient. I followed the additions for white wine, which is 1 gram per liter broken into two additions. That works out to one addition of about 11 or 12 grams before the yeast is added and another 11 or 12 grams one-third of the way through fermentation, at specific gravity 1.047 SG.

Yeast Pitch Rate

Click here to see the recipe that we are fermenting. It’s a 1.070 SG sugar wash with yeast nutrient added. I took the advice of the guy at the local homebrew supply store. “One 5 gram package of yeast will do 6 gallons.” he said. I put 5 grams of hydrated yeast in each of the four 6 gallon batches and put the fermentors to rest in my closet. Eight days went by and the specific gravity was only 1.055 SG. Something was wrong.

Maybe the yeast pitch rate was the issue. I searched the internet home distiller forums which said to use 4 grams of yeast per gallon of 8 to 10% ABV wash, which works out to 24 grams for my wash. This sounded high to me given that I’ve fermented strong beers with less yeast.

I fired up BeerSmith and doctored up a 1.070 SG sugar wash. BeerSmith said about 16 grams of dry yeast was recommended. I thought the truth may lie somewhere in between the two recommendations.

I added additional yeast to each fermenter to get amounts listed below. I also added the second nutrient addition just in case nutrients were the cause of the slow down in fermentation.

1. Batch 1 – Now had a total of 24 grams of yeast.
2. Batch 2 – Now had a total of 20 grams of yeast.
3. Batch 3 – Now had a total of 18 grams of yeast.
4. Batch 4 – Now had a total of 16 grams of yeast.

In the time-lapse video (coming soon) you can see the glass fermenter (batch 1) blow yeast through the blow off hose, yet two days later the specific gravity had barely fallen at all. The new pH test strips came in the mail and the pH was now reading 3.0. I added 1 tsp baking soda, and to my surprise, the fermentation rate skyrocketed.

Check out the table graphs below. I took the derivative of the specific gravity readings to get the rate of sugar consumption. On the graphs, I marked the yeast addition with diamonds, and each 1 tsp baking soda addition is marked with a dot.

Note: All specific gravity measurements are unadjusted and taken at 25 degrees Celsius with a hydrometer calibrated for 20 degrees Celsius.

Day/Time	SG	SG Rate of Change	pH	Event
2019/01/06 12:00	1.070			5g Yeast/12g Superfood
2019/01/08 12:00	1.064	0.00300
2019/01/10 12:00	1.062	0.00100
2019/01/14 12:00	1.055	0.00175	3.00	19g Yeast/12g Superfood
2019/01/16 12:00	1.054	0.00050	3.00	1 tsp baking soda
2019/01/18 12:00	1.042	0.00600	3.75	1 tsp baking soda
2019/01/19 12:40	1.037	0.00486	4.00
2019/01/20 19:41	1.032	0.00387	3.50
2019/01/22 13:26	1.024	0.00460	3.50
2019/01/24 11:25	1.016	0.00418	3.50
2019/01/25 19:10	1.012	0.00302	3.50	1 tsp baking soda
2019/01/26 19:52	1.009	0.00291	4.00
2019/01/28 12:00	1.006	0.00179	3.50
2019/01/30 12:00	1.002	0.00200	3.50
2019/02/02 12:00	0.994	0.00267	3.50
2019/02/04 22:13	0.992	0.00082	3.50
2019/02/06 22:18	0.992	0.00000	3.50

I never would have thought that pH would affect fermentation rate so much. I have read a theory online that the pH changes the shape of enzymes stopping the metabolic activity. Whatever the reason, I will try making a pH buffer in the next round of sugar wash and see how that affects things.

On February 6th, all four fermenters had a specific gravity of 0.992 unadjusted (0.994 SG adjusted), leading me to believe that BeerSmith was correct in recommending 16 grams of dry yeast. I will make 16 grams my next midpoint for pitch rates during the next round of sugar wash, underpitching and overpitching from there.

Since pH is such a large factor in the fermentation process I will be trying out different methods of maintaining pH throughout fermentation.