A yeast culture will almost always experience a lag phase where it consumes O2 and builds ergosterol and unsaturated fatty acid reserves. What differs is the number of replication periods it takes to reach maximum cell density when one overpitches.
Let’s start with the math. Nineteen liters (five gallons) of wort has a maximum cell density of approximately 200,000,000,000 * 19 = 3.8 trillion cells.
Batch size = 19L
Batch_Maximum_Cell_Density = 19 * 200,000,000,000 = 3.8 trillion
Pitched_Cell_Count = 200 billion
Replication_Periods = log(3800 / 200) / log(2) = log(19) / log(2) = 4.25 replication periods
Batch size = 19L
Batch_Maximum_Cell_Density = 19 * 200,000,000,000 = 3.8 trillion
Pitched_Cell_Count = 400 billion
Replication_Periods = log(3800 / 400) / log(2) = log(9.5) / log(2) = 3.25 replication periods
Batch size = 19L
Batch_Maximum_Cell_Density = 19 * 200,000,000,000 = 3.8 trillion
Pitched_Cell_Count = 800 billion
Replication_Periods = log(3800 / 800) / log(2) = log(4.75) / log(2) = 2.25 replication periods
Batch size = 19L
Batch_Maximum_Cell_Density = 19 * 200,000,000,000 = 3.8 trillion
Pitched_Cell_Count = 1.6 billion
Replication_Periods = log(3.8 / 1.6) / log(2) = log(2.375) / log(2) = 1.25 replication periods
As one can see, doubling the pitch rate reduces the replication period count by one.
How do these pitched cell counts translate to thick slurry? The generally accepted cell count per milliliter of thick slurry is 1.2 billion cells.
Pitch_200_Billion_Cells = 200 / 1.2 = 167ml
Pitch_400_Billion_Cells = 400 / 1.2 = 334ml
Pitch_800_Billion_Cells = 800 / 1.2 = 667ml
Pitch_1600_Billion_Cells = 1600 / 1.2 = 1334ml
If we follow the standard practice of cropping from the middle of the cake, we have mostly new cells with a pitch rate of 200B cells. The new cell count is reduced slightly with a pitching rate of 400B cells. However, after we get to 800B cells, we are looking at a minimum of 21% old cells even if we crop perfectly. By the time we get to 1.6T cells, half of the cropped cells are old. Old yeast cells are susceptible to the build up of something known as reactive oxygen species (ROS). ROS can cause damage to DNA and RNA, not to mention cell death.